REsource LOcation And Discovery (RELOAD) Base
ProtocolCisco170 West Tasman DriveMS: SJC-21/2San JoseCA95134USA+1 408 421-9990fluffy@cisco.comunaffiliated2790 Linden LnWilliamsburgVA23185USAbbl@lowekamp.netNetwork Resonance2064 Edgewood DrivePalo AltoCA94303USA+1 650 320-8549ekr@networkresonance.comColumbia University1214 Amsterdam AvenueNew YorkNYUSAsalman@cs.columbia.eduColumbia University1214 Amsterdam AvenueNew YorkNYUSAhgs@cs.columbia.edu
RAI
P2PSIPIn this document the term BCP 78 and BCP 79 refer to RFC 3978 and RFC
3979 respectively. They refer only to those RFCs and not any documents
that update or supersede them.This document defines REsource LOcation And Discovery (RELOAD), a
peer-to-peer (P2P) signaling protocol for use on the Internet. A P2P
signaling protocol provides its clients with an abstract storage and
messaging service between a set of cooperating peers that form the
overlay network. RELOAD is designed to support a P2P Session Initiation
Protocol (P2PSIP) network, but can be utilized by other applications
with similar requirements by defining new usages that specify the kinds
of data that must be stored for a particular application. RELOAD defines
a security model based on a certificate enrollment service that provides
unique identities. NAT traversal is a fundamental service of the
protocol. RELOAD also allows access from "client" nodes that do not need
to route traffic or store data for others.This documents and the information contained therein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION THEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.This document defines REsource LOcation And Discovery (RELOAD), a
peer-to-peer (P2P) signaling protocol for use on the Internet. It
provides a generic, self-organizing overlay network service, allowing
nodes to efficiently route messages to other nodes and to efficiently
store and retrieve data in the overlay. RELOAD provides several features
that are critical for a successful P2P protocol for the Internet:A P2P network will often be
established among a set of peers that do not trust each other.
RELOAD leverages a central enrollment server to provide credentials
for each peer which can then be used to authenticate each operation.
This greatly reduces the possible attack surface.RELOAD is designed to support a variety
of applications, including P2P multimedia communications with the
Session Initiation Protocol . RELOAD allows the definition
of new application usages, each of which can define its own data
types, along with the rules for their use. This allows RELOAD to be
used with new applications through a simple documentation process
that supplies the details for each application.RELOAD is designed to function in
environments where many if not most of the nodes are behind NATs or
firewalls. Operations for NAT traversal are part of the base design,
including using ICE to establish new RELOAD or application protocol
connections.The very nature of overlay
algorithms introduces a requirement that peers participating in the
P2P network route requests on behalf of other peers in the network.
This introduces a load on those other peers, in the form of
bandwidth and processing power. RELOAD has been defined with a
simple, lightweight forwarding header, thus minimizing the amount of
effort required by intermediate peers.RELOAD has been designed
with an abstract interface to the overlay layer to simplify
implementing a variety of structured (DHT) and unstructured overlay
algorithms. This specification also defines how RELOAD is used with
Chord, which is mandatory to implement. Specifying a default "must
implement" overlay algorithm will allow interoperability, while the
extensibility allows selection of overlay algorithms optimized for a
particular application.These properties were designed specifically to meet the requirements
for a P2P protocol to support SIP. This document defines the base
protocol for the distributed storage and location service, as well as
critical usages for NAT traversal and security. The SIP Usage itself is
described separately in .
RELOAD is not limited to usage by SIP and could serve as a tool for
supporting other P2P applications with similar needs. RELOAD is also
based on the concepts introduced in .In this section, we provide a brief overview of the operational
setting for RELOAD. See the concepts document for more details. A
RELOAD Overlay Instance consists of a set of nodes arranged in a
partly connected graph. Each node in the overlay is assigned a numeric
Node-ID which, together with the specific overlay algorithm in use,
determines its position in the graph and the set of nodes it connects
to. The figure below shows a trivial example which isn't drawn from
any particular overlay algorithm, but was chosen for convenience of
representation.Because the graph is not fully connected, when a node wants to send
a message to another node, it may need to route it through the
network. For instance, Node 10 can talk directly to nodes 20 and 40,
but not to Node 70. In order to send a message to Node 70, it would
first send it to Node 40 with instructions to pass it along to Node
70. Different overlay algorithms will have different connectivity
graphs, but the general idea behind all of them is to allow any node
in the graph to efficiently reach every other node within a small
number of hops.The RELOAD network is not only a messaging network. It is also a
storage network. Records are stored under numeric addresses which
occupy the same space as node identifiers. Nodes are responsible for
storing the data associated with some set of addresses as determined
by their Node-ID. For instance, we might say that every node is
responsible for storing any data value which has an address less than
or equal to its own Node-ID, but greater than the next lowest Node-ID.
Thus, Node-20 would be responsible for storing values 11-20.RELOAD also supports clients. These are nodes which have Node-IDs
but do not participate in routing or storage. For instance, in the
figure above Node 85 is a client. It can route to the rest of the
RELOAD network via Node 80, but no other node will route through it
and Node 90 is still responsible for all addresses between 81-90. We
refer to non-client nodes as peers.Other applications (for instance, SIP) can be defined on top of
RELOAD and use these two basic RELOAD services to provide their own
services.RELOAD is fundamentally an overlay network. Therefore, it can be
divided into components that mimic the layering of the Internet
model.| Storage |
| Transport | +---------+
+------------------+ ^
^ ^ |
| v v
| +-------------------+
| | Topology |
| | Plugin |
| +-------------------+
| ^
v v
+------------------+
| Forwarding & |
| Link Management |
+------------------+
-------------------------------------- Overlay Link API
+-------+ +------+
|TLS | |DTLS | ...
+-------+ +------+
]]>The major components of RELOAD are:Each application defines a RELOAD
usage; a set of data kinds and behaviors which describe how to use
the services provided by RELOAD. These usages all talk to RELOAD
through a common Message Transport API.Handles the end-to-end
reliability, manages request state for the usages, and forwards
Store and Fetch operations to the Storage component. Delivers
message responses to the component initiating the request.The Storage component is responsible for
processing messages relating to the storage and retrieval of data.
It talks directly to the Topology Plugin to manage data
replication and migration, and it talks to the Message Transport
to send and receive messages.The Topology Plugin is responsible
for implementing the specific overlay algorithm being used. It
uses the Message Transport component to send and receive overlay
management messages, to the Storage component to manage data
replication, and directly to the Forwarding Layer to control
hop-by-hop message forwarding. This component closely parallels
conventional routing algorithms, but is more tightly coupled to
the Forwarding Layer because there is no single "routing table"
equivalent used by all overlay algorithms.Stores and
implements the routing table by providing packet forwarding
services between nodes. It also handles establishing new links
between nodes, including setting up connections across NATs using
ICE.TLS
and DTLS are the "link
layer" protocols used by RELOAD for hop-by-hop communication. Each
such protocol includes the appropriate provisions for per-hop
framing or hop-by-hop ACKs required by unreliable transports.To further clarify the roles of the various layer, this figure
parallels the architecture with each layer's role from an overlay
perspective and implementation layer in the internet:| Storage |
| || Transport | +---------+
| |+------------------+ ^
| | ^ ^ |
| | | v v
Application | | | +-------------------+
| (Routing) | | | Topology |
| | | | Plugin |
| | | +-------------------+
| | v ^
| | v
| Network | +------------------+
| | | Forwarding & |
| | | Link Management |
| | +------------------+
| | ----------------------------------
Transport | Link | +-------+ +------+
| | |TLS | |DTLS | ...
| | +-------+ +------+
--------------+-----------------+------------------------------------
Network |
|
Link |
]]>The top layer, called the Usage Layer, has application usages,
such as the SIP Location Usage, that use the abstract Message
Transport API provided by RELOAD. The goal of this layer is to
implement application-specific usages of the generic overlay
services provided by RELOAD. The usage defines how a specific
application maps its data into something that can be stored in the
overlay, where to store the data, how to secure the data, and
finally how applications can retrieve and use the data.The architecture diagram shows both a SIP usage and an XMPP
usage. A single application may require multiple usages, for example
a SIP application may also require a voicemail usage. A usage may
define multiple kinds of data that are stored in the overlay and may
also rely on kinds originally defined by other usages.Because the security and storage policies for each kind are
dictated by the usage defining the kind, the usages may be coupled
with the Storage component to provide security policy enforcement
and to implement appropriate storage strategies according to the
needs of the usage. The exact implementation of such an interface is
outside the scope of this draft.The Message Transport provides a generic message routing service
for the overlay. The Message Transport layer is responsible for
end-to-end message transactions, including retransmissions. Each
peer is identified by its location in the overlay as determined by
its Node-ID. A component that is a client of the Message Transport
can perform two basic functions:Send a message to a given peer specified by Node-ID or to the
peer responsible for a particular Resource-ID.Receive messages that other peers sent to a Node-ID or
Resource-ID for which this peer is responsible.All usages rely on the Message Transport component to send and
receive messages from peers. For instance, when a usage wants to
store data, it does so by sending Store requests. Note that the
Storage component and the Topology Plugin are themselves clients of
the Message Transport, because they need to send and receive
messages from other peers.The Message Transport API is similar to those described as
providing "Key based routing" (KBR), although as RELOAD supports
different overlay algorithms (including non-DHT overlay algorithms)
that calculate keys in different ways, the actual interface must
accept Resource Names rather than actual keys.One of the major functions of RELOAD is to allow nodes to store
data in the overlay and to retrieve data stored by other nodes or by
themselves. The Storage component is responsible for processing data
storage and retrieval messages. For instance, the Storage component
might receive a Store request for a given resource from the Message
Transport. It would then query the appropriate usage before storing
the data value(s) in its local data store and sends a response to
the Message Transport for delivery to the requesting peer.
Typically, these messages will come for other nodes, but depending
on the overlay topology, a node might be responsible for storing
data for itself as well, especially if the overlay is small.A peer's Node-ID determines the set of resources that it will be
responsible for storing. However, the exact mapping between these is
determined by the overlay algorithm used by the overlay. The Storage
component will only receive a Store request from the Message
Transport if this peer is responsible for that Resource-ID. The
Storage component is notified by the Topology Plugin when the
Resource-IDs for which it is responsible change, and the Storage
component is then responsible for migrating resources to other
peers, as required.RELOAD is explicitly designed to work with a variety of overlay
algorithms. In order to facilitate this, the overlay algorithm
implementation is provided by a Topology Plugin so that each overlay
can select an appropriate overlay algorithm that relies on the
common RELOAD core protocols and code.The Topology Plugin is responsible for maintaining the overlay
algorithm Routing Table, which is consulted by the Forwarding and
Link Management Layer before routing a message. When connections are
made or broken, the Forwarding and Link Management Layer notifies
the Topology Plugin, which adjusts the routing table as appropriate.
The Topology Plugin will also instruct the Forwarding and Link
Management Layer to form new connections as dictated by the
requirements of the overlay algorithm Topology. The Topology Plugin
issues periodic update requests through Message Transport to
maintain and update its Routing Table.As peers enter and leave, resources may be stored on different
peers, so the Topology Plugin also keeps track of which peers are
responsible for which resources. As peers join and leave, the
Topology Plugin instructs the Storage component to issue resource
migration requests as appropriate, in order to ensure that other
peers have whatever resources they are now responsible for. The
Topology Plugin is also responsible for providing redundant data
storage to protect against loss of information in the event of a
peer failure and to protect against compromised or subversive
peers.The Forwarding and Link Management Layer is responsible for
getting a packet to the next peer, as determined by the Topology
Plugin. This Layer establishes and maintains the network connections
as required by the Topology Plugin. This layer is also responsible
for setting up connections to other peers through NATs and firewalls
using ICE, and it can elect to forward traffic using relays for NAT
and firewall traversal.This layer provides a fairly generic interface that allows the
topology plugin control the overlay and resource operations and
messages. Since each overlay algorithm is defined and functions
differently, we generically refer to the table of other peers that
the overlay algorithm maintains and uses to route requests
(neighbors) as a Routing Table. The Topology Plugin actually owns
the Routing Table, and forwarding decisions are made by querying the
Topology Plugin for the next hop for a particular Node-ID or
Resource-ID. If this node is the destination of the message, the
message is delivered to the Message Transport.The Forwarding and Link Management Layer sits on top of the
Overlay Link Layer protocols that carry the actual traffic. This
specification defines how to use DTLS and TLS protocols to carry
RELOAD messages.RELOAD's security model is based on each node having one or more
public key certificates. In general, these certificates will be
assigned by a central server which also assigns Node-IDs, although
self-signed certificates can be used in closed networks. These
credentials can be leveraged to provide communications security for
RELOAD messages. RELOAD provides communications security at three
levels:Connections between peers are
secured with TLS or DTLS.Each RELOAD message must be
signed.Stored objects must be signed by the
storing peer.These three levels of security work together to allow peers to
verify the origin and correctness of data they receive from other
peers, even in the face of malicious activity by other peers in the
overlay. RELOAD also provides access control built on top of these
communications security features. Because the peer responsible for
storing a piece of data can validate the signature on the data being
stored, the responsible peer can determine whether a given operation
is permitted or not.RELOAD also provides a shared secret based admission control
feature using shared secrets and TLS-PSK. In order to form a TLS
connection to any node in the overlay, a new node needs to know the
shared overlay key, thus restricting access to authorized users.The remainder of this document is structured as follows. provides definitions of terms
used in this document. provides an
overview of the mechanisms used to establish and maintain the
overlay. provides an overview of
the mechanism RELOAD provides to support other applications. defines the
protocol messages that RELOAD uses to establish and maintain the
overlay. defines the protocol
messages that are used to store and retrieve data using
RELOAD. defines the Certificate
Store Usage that is fundamental to RELOAD security. defines the TURN Server
Usage needed to locate TURN servers for NAT traversal. defines a specific
Topology Plugin using Chord. defines the mechanisms
that new RELOAD nodes use to join the overlay for the first
time. provides an extended
example.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.We use the terminology and definitions from the Concepts and Terminology for Peer to
Peer SIP draft extensively in this document. Other terms used in
this document are defined inline when used and are also defined below
for reference. Terms which are new to this document (and perhaps should
be added to the concepts document) are marked with a (*).A distributed hash table. A DHT is an abstract
hash table service realized by storing the contents of the hash
table across a set of peers.An overlay algorithm defines the
rules for determining which peers in an overlay store a particular
piece of data and for determining a topology of interconnections
amongst peers in order to find a piece of data.A specific overlay algorithm and the
collection of peers that are collaborating to provide read and write
access to it. There can be any number of overlay instances running
in an IP network at a time, and each operates in isolation of the
others.A host that is participating in the overlay.
Peers are responsible for holding some portion of the data that has
been stored in the overlay and also route messages on behalf of
other hosts as required by the Overlay Algorithm.A host that is able to store data in and
retrieve data from the overlay but which is not participating in
routing or data storage for the overlay.We use the term "Node" to refer to a host that
may be either a Peer or a Client. Because RELOAD uses the same
protocol for both clients and peers, much of the text applies
equally to both. Therefore we use "Node" when the text applies to
both Clients and Peers and the more specific term when the text
applies only to Clients or only to Peers.A 128-bit value that uniquely identifies a
node. Node-IDs 0 and 2^128 - 1 are reserved and are invalid
Node-IDs. A value of zero is not used in the wire protocol but can
be used to indicate an invalid node in implementations and APIs. The
Node-ID of 2^128-1 is used on the wire protocol as a wildcard.
(*)An object or group of objects associated
with a string identifier see "Resource Name" below.The potentially human readable name by
which a resource is identified. In unstructured P2P networks, the
resource name is sometimes used directly as a Resource-ID. In
structured P2P networks the resource name is typically mapped into a
Resource-ID by using the string as the input to hash function. A SIP
resource, for example, is often identified by its AOR which is an
example of a Resource Name.(*)A value that identifies some resources
and which is used as a key for storing and retrieving the resource.
Often this is not human friendly/readable. One way to generate a
Resource-ID is by applying a mapping function to some other unique
name (e.g., user name or service name) for the resource. The
Resource-ID is used by the distributed database algorithm to
determine the peer or peers that are responsible for storing the
data for the overlay. In structured P2P networks, Resource-IDs are
generally fixed length and are formed by hashing the resource name.
In unstructured networks, resource names may be used directly as
Resource-IDs and may have variable length.The set of peers to which a node is
directly connected. This includes nodes with which Attach handshakes
have been done but which have not sent any Updates.The set of peers which a node can use
to route overlay messages. In general, these peers will all be on
the connection table but not vice versa, because some peers will
have Attached but not sent updates. Peers may send messages directly
to peers which are on the connection table but may only route
messages to other peers through peers which are on the routing
table. (*)A list of IDs through which a
message is to be routed. A single Node-ID is a trivial form of
destination list. (*)A usage is an application that wishes to use
the overlay for some purpose. Each application wishing to use the
overlay defines a set of data kinds that it wishes to use. The SIP
usage defines the location data kind. (*)The most basic function of RELOAD is as a generic overlay network.
Nodes need to be able to join the overlay, form connections to other
nodes, and route messages through the overlay to nodes to which they are
not directly connected. This section provides an overview of the
mechanisms that perform these functions.Every node in the RELOAD overlay is identified by a Node-ID. The
Node-ID is used for three major purposes:To address the node itself.To determine its position in the overlay topology when the
overlay is structured.To determine the set of resources for which the node is
responsible.Each node has a certificate
containing a Node-ID, which is globally unique.The certificate serves multiple purposes:It entitles the user to store data at specific locations in the
Overlay Instance. Each data kind defines the specific rules for
determining which certificates can access each Resource-ID/Kind-ID
pair. For instance, some kinds might allow anyone to write at a
given location, whereas others might restrict writes to the owner
of a single certificate.It entitles the user to operate a node that has a Node-ID found
in the certificate. When the node forms a connection to another
peer, it can use this certificate so that a node connecting to it
knows it is connected to the correct node. In addition, the node
can sign messages, thus providing integrity and authentication for
messages which are sent from the node.It entitles the user to use the user name found in the
certificate.If a user has more than one device, typically they would get one
certificate for each device. This allows each device to act as a
separate peer.RELOAD supports two certificate issuance models. The first is based
on a central enrollment process which allocates a unique name and
Node-ID to the node a certificate for a public/private key pair for
the user. All peers in a particular Overlay Instance have the
enrollment server as a trust anchor and so can verify any other peer's
certificate.In some settings, a group of users want to set up an overlay
network but are not concerned about attack by other users in the
network. For instance, users on a LAN might want to set up a short
term ad hoc network without going to the trouble of setting up an
enrollment server. RELOAD supports the use of self-generated and
self-signed certificates. When self-signed certificates are used, the
node also generates its own Node-ID and username. The Node-ID is
computed as a digest of the public key, to prevent Node-ID theft,
however this model is still subject to a number of known attacks (most
notably Sybil attacks ) and can only be
safely used in closed networks where users are mutually trusting.The general principle here is that the security mechanisms (TLS and
message signatures) are always used, even if the certificates are
self-signed. This allows for a single set of code paths in the systems
with the only difference being whether certificate verification is
required to chain to a single root of trust.RELOAD also provides an admission control system based on shared
keys. In this model, the peers all share a single key which is used
to authenticate the peer-to-peer connections via
TLS-PSK/TLS-SRP.RELOAD defines a single protocol that is used both as the peer
protocol and the client protocol for the overlay. This simplifies
implementation, particularly for devices that may act in either role,
and allows clients to inject messages directly into the overlay.We use the term "peer" to identify a node in the overlay that
routes messages for nodes other than those to which it is directly
connected. Peers typically also have storage responsibilities. We use
the term "client" to refer to nodes that do not have routing or
storage responsibilities. When text applies to both peers and clients,
we will simply refer to such a device as a "node."RELOAD's client support allows nodes that are not participating in
the overlay as peers to utilize the same implementation and to benefit
from the same security mechanisms as the peers. Clients possess and
use certificates that authorize the user to store data at its
locations in the overlay. The Node-ID in the certificate is used to
identify the particular client as a member of the overlay and to
authenticate its messages.For more discussion of the motivation for RELOAD's client support,
see .There are two routing options by which a client may be located in
an overlay.Establish a connection to the peer responsible for the
client's Node-ID in the overlay. Then requests may be sent
from/to the client using its Node-ID in the same manner as if it
were a peer, because the responsible peer in the overlay will
handle the final step of routing to the client. This will not
work in overlays where NAT or firewall do not allow all clients
to form connections with any other peer.Establish a connection with an arbitrary peer in the overlay
(perhaps based on network proximity or an inability to establish
a direct connection with the responsible peer). In this case,
the client will rely on RELOAD's Destination List feature to
ensure reachability. The client can initiate requests, and any
node in the overlay that knows the Destination List to its
current location can reach it, but the client is not directly
reachable directly using only its Node-ID. The Destination List
required to reach it must be learnable via other mechanisms,
such as being stored in the overlay by a usage, if the client is
to receive incoming requests from other members of the
overlay.A node may act as a client simply because it does not have the
resources or even an implementation of the topology plugin required
to acts as a peer in the overlay. In order to exchange RELOAD
messages with a peer, a client must meet a minimum level of
functionality. Such a client must:Implement RELOAD's connection-management connections that are
used to establish the connection with the peer.Implement RELOAD's data retrieval methods (with client
functionality).Be able to calculate Resource-IDs used by the overlay.Possess security credentials required by the overlay it is
implementing.A client speaks the same protocol as the peers, knows how to
calculate Resource-IDs, and signs its requests in the same manner as
peers. While a client does not necessarily require a full
implementation of the overlay algorithm, calculating the Resource-ID
requires an implementation of the appropriate algorithm for the
overlay.RELOAD does not support a separate protocol for clients that do
not meet these functionality requirements. Any such extension would
either entail compromises on the features of RELOAD or require an
entirely new protocol to reimplement the core features of RELOAD.
Furthermore, for SIP and many other applications, a native
application-level protocol already exists that is sufficient for
such a client to interact with a member of the RELOAD overlay.This section will discuss the requirements RELOAD's routing
capabilities must meet, then describe the routing features in the
protocol, and provide a brief overview of how they are used. discusses some alternative designs and
the tradeoffs that would be necessary to support them.RELOAD's routing capabilities must meet the following
requirements:RELOAD must support establishing and
using connections between nodes separated by one or more NATs,
including locating peers behind NATs for those overlays
allowing/requiring it.RELOAD must support requests from and to
clients that do not participate in overlay routing.RELOAD must support clients that
become peers at a later point as determined by the overlay
algorithm and deployment.RELOAD's routing algorithms must not
require significant state to be stored on intermediate peers.At some
points in times, different nodes may have inconsistent information
about the connectivity of the routing graph. In all cases, the
response to a request needs to delivered to the node that sent the
request and not to some other node.To meet these requirements, RELOAD's routing relies on two basic
mechanisms:The forwarding header used by all RELOAD
messages contains both a Via List (built hop-by-hop as the message
is routed through the overlay) and a Destination List (providing
source-routing capabilities for requests and return-path routing
for responses).The Route_Query method allows a node
to query a peer for the next hop it will use to route a message.
This method is useful for diagnostics and for iterative
routing.The basic routing mechanism used by RELOAD is Symmetric Recursive.
We will first describe symmetric routing and then discuss its
advantages in terms of the requirements discussed above.Symmetric recursive routing requires a message follow the path
through the overlay to the destination without returning to the
originating node: each peer forwards the message closer to its
destination. The return path of the response is then the same path
followed in reverse. For example, a message following a route from A
to Z through B and X:
Dest=Z
---------->
Via=A
Dest=Z
---------->
Via=A, B
Dest=Z
<----------
Dest=X, B, A
<----------
Dest=B, A
<----------
Dest=A
]]>Note that the preceding Figure does not indicate whether A is a
client or peer, A forwards its request to B and the response is
returned to A in the same manner regardless of A's role in the
overlay.This figure shows use of full via-lists by intermediate peers B and
X. However, if B and/or X are willing to store state, then they may
elect to truncate the lists, save that information internally (keyed
by the transaction id), and return the response message along the path
from which it was received when the response is received. This option
requires greater state on intermediate peers but saves a small amount
of bandwidth and reduces the need for modifying the message in route.
Selection of this mode of operation is a choice for the individual
peer, the techniques are interoperable even on a single message. The
figure below shows B using full via lists but X truncating them and
saving the state internally.
Dest=Z
---------->
Via=A
Dest=Z
---------->
Dest=Z
<----------
Dest=X
<----------
Dest=B, A
<----------
Dest=A
]]>For debugging purposes, a Route Log attribute is available that
stores information about each peer as the message is forwarded.RELOAD also supports a basic Iterative routing mode (where the
intermediate peers merely return a response indicating the next hop,
but do not actually forward the message to that next hop themselves).
Iterative routing is implemented using the Route_Query method, which
requests this behavior. Note that iterative routing is selected only
by the initiating node. RELOAD does not support an intermediate peer
returning a response that it will not recursively route a normal
request. The willingness to perform that operation is implicit in its
role as a peer in the overlay.In order to provide efficient routing, a peer needs to maintain a
set of direct connections to other peers in the Overlay Instance. Due
to the presence of NATs, these connections often cannot be formed
directly. Instead, we use the Attach request to establish a
connection. Attach uses ICE to establish the connection.
It is assumed that the reader is familiar with ICE.Say that peer A wishes to form a direct connection to peer B. It
gathers ICE candidates and packages them up in an Attach request which
it sends to B through usual overlay routing procedures. B does its own
candidate gathering and sends back a response with its candidates. A
and B then do ICE connectivity checks on the candidate pairs. The
result is a connection between A and B. At this point, A and B can add
each other to their routing tables and send messages directly between
themselves without going through other overlay peers.There is one special case in which Attach cannot be used: when a
peer is joining the overlay and is not connected to any peers. In
order to support this case, some small number of "bootstrap nodes"
need to be publicly accessible so that new peers can directly connect
to them. contains more detail on
this.In general, a peer needs to maintain connections to all of the
peers near it in the Overlay Instance and to enough other peers to
have efficient routing (the details depend on the specific overlay).
If a peer cannot form a connection to some other peer, this isn't
necessarily a disaster; overlays can route correctly even without
fully connected links. However, a peer should try to maintain the
specified link set and if it detects that it has fewer direct
connections, should form more as required. This also implies that
peers need to periodically verify that the connected peers are still
alive and if not try to reform the connection or form an alternate
one.The Topology Plugin allows RELOAD to support a variety of overlay
algorithms. This draft defines a DHT based on Chord , which is mandatory to implement, but the base
RELOAD protocol is designed to support a variety of overlay
algorithms.RELOAD defines three methods for overlay maintenance: Join,
Update, and Leave. However, the contents of those messages, when
they are sent, and their precise semantics are specified by the
actual overlay algorithm; RELOAD merely provides a framework of
commonly-needed methods that provides uniformity of notation (and
ease of debugging) for a variety of overlay algorithms.When a new peer wishes to join the Overlay Instance, it must have
a Node-ID that it is allowed to use. It uses the Node-ID in the
certificate it received from the enrollment server. The details of
the joining procedure are defined by the overlay algorithm, but the
general steps for joining an Overlay Instance are:Forming connections to some other peers.Acquiring the data values this peer is responsible for
storing.Informing the other peers which were previously responsible
for that data that this peer has taken over responsibility.The first thing the peer needs to do is form a connection to some
"bootstrap node". Because this is the first connection the peer
makes, these nodes must have public IP addresses and therefore can
be connected to directly. Once a peer has connected to one or more
bootstrap nodes, it can form connections in the usual way by routing
Attach messages through the overlay to other nodes. Once a peer has
connected to the overlay for the first time, it can cache the set of
nodes it has connected to with public IP addresses for use as future
bootstrap nodes.Once the peer has connected to a bootstrap node, it then needs to
take up its appropriate place in the overlay. This requires two
major operations:Forming connections to other peers in the overlay to populate
its Routing Table.Getting a copy of the data it is now responsible for storing
and assuming responsibility for that data.The second operation is performed by contacting the Admitting
Peer (AP), the node which is currently responsible for that section
of the overlay.The details of this operation depend mostly on the overlay
algorithm involved, but a typical case would be:JP (Joining Peer) sends a Join request to AP (Admitting Peer)
announcing its intention to join.AP sends a Join response.AP does a sequence of Stores to JP to give it the data it
will need.AP does Updates to JP and to other peers to tell it about its
own routing table. At this point, both JP and AP consider JP
responsible for some section of the Overlay Instance.JP makes its own connections to the appropriate peers in the
Overlay Instance.After this process is completed, JP is a full member of the
Overlay Instance and can process Store/Fetch requests.Note that the first node is a special case. When ordinary nodes
cannot form connections to the bootstrap nodes, then they are not
part of the overlay. However, the first node in the overlay can
obviously not connect to others nodes. In order to support this
case, potential first nodes (which must also serve as bootstrap
nodes initially) must somehow be instructed (perhaps by
configuration settings) that they are the entire overlay, rather
than not part of it.Previous sections addressed how RELOAD works once a node has
connected. This section provides an overview of how users get
connected to the overlay for the first time. RELOAD is designed so
that users can start with the name of the overlay they wish to join
and perhaps a username and password, and leverage that into having a
working peer with minimal user intervention. This helps avoid the
problems that have been experienced with conventional SIP clients
where users are required to manually configure a large number of
settings.In the first phase of the process, the user starts out with the
name of the overlay and uses this to download an initial set of
overlay configuration parameters. The user does a DNS SRV lookup on
the overlay name to get the address of a configuration server. It
can then connect to this server with HTTPS to download a
configuration document which contains the basic overlay
configuration parameters as well as a set of bootstrap nodes which
can be used to join the overlay.If the overlay is using centralized enrollment, then a user needs
to acquire a certificate before joining the overlay. The certificate
attests both to the user's name within the overlay and to the
Node-IDs which they are permitted to operate. In that case, the
configuration document will contain the address of an enrollment
server which can be used to obtain such a certificate. The
enrollment server may (and probably will) require some sort of
username and password before issuing the certificate. The enrollment
server's ability to restrict attackers' access to certificates in
the overlay is one of the cornerstones of RELOAD's security.RELOAD is not intended to be used alone, but rather as a substrate
for other applications. These applications can use RELOAD for a variety
of purposes:To store data in the overlay and retrieve data stored by other
nodes.As a discovery mechanism for services such as TURN.To form direct connections which can be used to transmit
application-level messages.This section provides an overview of these services.RELOAD provides operations to Store and Fetch data. Each location
in the Overlay Instance is referenced by a Resource-ID. However, each
location may contain data elements corresponding to multiple kinds
(e.g., certificate, SIP registration). Similarly, there may be
multiple elements of a given kind, as shown below:Each kind is identified by a Kind-ID, which is a code point
assigned by IANA. As part of the kind definition, protocol designers
may define constraints, such as limits on size, on the values which
may be stored. For many kinds, the set may be restricted to a single
value; some sets may be allowed to contain multiple identical items
while others may only have unique items. Note that a kind may be
employed by multiple usages and new usages are encouraged to use
previously defined kinds where possible. We define the following data
models in this document, though other usages can define their own
structures:There can be at most one item in the
set and any value overwrites the previous item.Many values can be stored and addressed by a
numeric index.The values stored are indexed by a key.
Often this key is one of the values from the certificate of the
peer sending the Store request.In order to protect stored data from tampering, by other nodes,
each stored value is digitally signed by the node which created it.
When a value is retrieved, the digital signature can be verified to
detect tampering.A major issue in peer-to-peer storage networks is minimizing the
burden of becoming a peer, and in particular minimizing the amount
of data which any peer is required to store for other nodes. RELOAD
addresses this issue by only allowing any given node to store data
at a small number of locations in the overlay, with those locations
being determined by the node's certificate. When a peer uses a Store
request to place data at a location authorized by its certificate,
it signs that data with the private key that corresponds to its
certificate. Then the peer responsible for storing the data is able
to verify that the peer issuing the request is authorized to make
that request. Each data kind defines the exact rules for determining
what certificate is appropriate.The most natural rule is that a certificate authorizes a user to
store data keyed with their user name X. This rules is used for all
the kinds defined in this specification. Thus, only a user with a
certificate for "alice@example.org" could write to that location in
the overlay. However, other usages can define any rules they choose,
including publicly writable values.The digital signature over the data serves two purposes. First,
it allows the peer responsible for storing the data to verify that
this Store is authorized. Second, it provides integrity for the
data. The signature is saved along with the data value (or values)
so that any reader can verify the integrity of the data. Of course,
the responsible peer can "lose" the value but it cannot undetectable
modify it.The size requirements of the data being stored in the overlay are
variable. For instance, a SIP AoR and voicemail differ widely in the
storage size. RELOAD leaves it to the Usage and overlay
configuration to address the size imbalance of various kinds.By itself, the distributed storage layer just provides
infrastructure on which applications are built. In order to do
anything useful, a usage must be defined. Each Usage specifies
several things:Registers Kind-ID code points for any kinds that the Usage
defines.Defines the data structure for each of the kinds.Defines access control rules for each kinds.Defines how the Resource Name is formed that is hashed to
form the Resource-ID where each kind is stored.Describes how values will be merged after a network
partition. Unless otherwise specified, the default merging rule
is to act as if all the values that need to be merged were
stored and that the order they were stored in corresponds to the
stored time values associated with (and carried in) their
values. Because the stored time values are those associated with
the peer which did the writing, clock skew is generally not an
issue. If two nodes are on different partitions, clocks, this
can create merge conflicts. However because RELOAD deliberately
segregates storage so that data from different users and peers
is stored in different locations, and a single peer will
typically only be in a single network partition, this case will
generally not arise.The kinds defined by a usage may also be applied to other usages.
However, a need for different parameters, such as different size
limits, would imply the need to create a new kind.Replication in P2P overlays can be used to provide:if the responsible peer crashes
and/or if the storing peer leaves the overlayto guard against DoS attacks by the
responsible peer or routing attacks to that responsible peerto balance the load of queries
for popular resources.A variety of schemes are used in P2P overlays to achieve some of
these goals. Common techniques include replicating on neighbors of
the responsible peer, randomly locating replicas around the overlay,
or replicating along the path to the responsible peer.The core RELOAD specification does not specify a particular
replication strategy. Instead, the first level of replication
strategies are determined by the overlay algorithm, which can base
the replication strategy on the its particular topology. For
example, Chord places replicas on successor peers, which will take
over responsibility should the responsible peer fail .If additional replication is needed, for example if data
persistence is particularly important for a particular usage, then
that usage may specify additional replication, such as implementing
random replications by inserting a different well known constant
into the Resource Name used to store each replicated copy of the
resource. Such replication strategies can be added independent of
the underlying algorithm, and their usage can be determined based on
the needs of the particular usage.RELOAD does not currently define a generic service discovery
algorithm as part of the base protocol; although a TURN-specific
discovery mechanism is provided. A variety of service discovery
algorithm can be implemented as extensions to the base protocol, such
as ReDIR .There is no requirement that a RELOAD usage must use RELOAD's
primitives for establishing its own communication if it already
possesses its own means of establishing connections. For example, one
could design a RELOAD-based resource discovery protocol which used
HTTP to retrieve the actual data.For more common situations, however, the overlay itself is used to
establish a connection rather than an external authority such as DNS,
RELOAD provides connectivity to applications using the same Attach
method as is used for the overlay maintenance. For example, if a
P2PSIP node wishes to establish a SIP dialog with another P2PSIP node,
it will use Attach to establish a direct connection with the other
node. This new connection is separate from the peer protocol
connection, it is a dedicated UDP or TCP flow used only for the SIP
dialog. Each usage specifies which types of connections can be
initiated using Attach.This section defines the basic protocols used to create, maintain,
and use the RELOAD overlay network. We start by defining the basic
concept of how message destinations are interpreted when routing
messages. We then describe the symmetric recursive routing model, which
is RELOAD's default routing algorithm. We then define the message
structure and then finally define the messages used to join and maintain
the overlay.When a peer receives a message, it first examines the overlay,
version, and other header fields to determine whether the message is
one it can process. If any of these are incorrect (e.g., the message
is for an overlay in which the peer does not participate) it is an
error. The peer SHOULD generate an appropriate error but local
policy can override this and cause the messages is silently
dropped.Once the peer has determined that the message is correctly
formatted, it examines the first entry on the destination list. There
are three possible cases here:The first entry on the destination list is an id for which the
peer is responsible.The first entry on the destination list is a an id for which
another peer is responsible.The first entry on the destination list is a private id which
is being used for destination list compression.These cases are handled as discussed below.If the first entry on the destination list is a ID for which the
node is responsible, there are several sub-cases. If the entry is a Resource-ID, then it MUST be the only entry
on the destination list. If there are other entries, the message
MUST be silently dropped. Otherwise, the message is destined for
this node and it passes it up to the upper layers.If the entry is a Node-ID which belongs to this node, then
the message is destined for this node. If this is the only entry
on the destination list, the message is destined for this node
and is passed up to the upper layers. Otherwise the entry is
removed from the destination list and the message is passed it
to the Message Transport. If the message is a response and there
is state for the transaction ID, the state is reinserted into
the destination list first.If the entry is a Node-ID which is not equal to this node,
then the node MUST drop the message silently unless the Node-ID
corresponds to a node which is directly connected to this node
(i.e., a client). In that case, it MUST forward the message to
the destination node as described in the next section.Note that this implies that in order to address a message to "the
peer that controls region X", a sender sends to Resource-ID X, not
Node-ID X.If neither of the other two cases applies, then the peer MUST
forward the message towards the first entry on the destination list.
This means that it MUST select one of the peers to which it is
connected and which is likely to be responsible for the first entry
on the destination list. If the first entry on the destination list
is in the peer's connection table, then it SHOULD forward the
message to that peer directly. Otherwise, it consult the routing
table to forward the message.Any intermediate peer which forwards a RELOAD message MUST
arrange that if it receives a response to that message the response
can be routed back through the set of nodes through which the
request passed. This may be arranged in one of two ways:The peer MAY add an entry to the via list in the forwarding
header that will enable it to determine the correct node.The peer MAY keep per-transaction state which will allow it
to determine the correct node.As an example of the first strategy, if node D receives a message
from node C with via list (A, B), then D would forward to the next
node (E) with via list (A, B, C). Now, if E wants to respond to the
message, it reverses the via list to produce the destination list,
resulting in (D, C, B, A). When D forwards the response to C, the
destination list will contain (C, B, A).As an example of the second strategy, if node D receives a
message from node C with transaction ID X and via list (A, B), it
could store (X, C) in its state database and forward the message
with the via list unchanged. When D receives the response, it
consults its state database for transaction id X, determines that
the request came from C, and forwards the response to C.Intermediate peer which modify the via list are not required to
simply add entries. The only requirement is that the peer be able to
reconstruct the correct destination list on the return route. RELOAD
provides explicit support for this functionality in the form of
private IDs, which can replace any number of via list entries. For
instance, in the above example, Node D might send E a via list
containing only the private ID (I). E would then use the destination
list (D, I) to send its return message. When D processes this
destination list, it would detect that I is a private ID, recover
the via list (A, B, C), and reverse that to produce the correct
destination list (C, B, A) before sending it to C. This feature is
called List Compression. I MAY either be a compressed version of the
original via list or an index into a state database containing the
original via list.Note that if an intermediate peer exits the overlay, then on the
return trip the message cannot be forwarded and will be dropped. The
ordinary timeout and retransmission mechanisms provide stability
over this type of failure.If the first entry on the destination list is a private id (e.g.,
a compressed via list), the peer MUST that entry with the original
via list that it replaced indexes and then re-examine the
destination list to determine which case now applies.This Section defines RELOAD's symmetric recursive routing
algorithm, which is the default algorithm used by nodes to route
messages through the overlay. All implementations MUST implement this
routing algorithm. An overlay may be configured to use alternative
routing algorithms, and alternative routing algorithms may be selected
on a per-message basis.In order to originate a message to a given Node-ID or
Resource-ID, a node constructs an appropriate destination list. The
simplest such destination list is a single entry containing the peer
or Resource-ID. The resulting message will use the normal overlay
routing mechanisms to forward the message to that destination. The
node can also construct a more complicated destination list for
source routing.Once the message is constructed, the node sends the message to
some adjacent peer. If the first entry on the destination list is
directly connected, then the message MUST be routed down that
connection. Otherwise, the topology plugin MUST be consulted to
determine the appropriate next hop.Parallel searches for the resource are a common solution to
improve reliability in the face of churn or of subversive peers.
Parallel searches for usage-specified replicas are managed by the
usage layer. However, a single request can also be routed through
multiple adjacent peers, even when known to be sub-optimal, to
improve reliability .
Such parallel searches MAY BE specified by the topology plugin.Because messages may be lost in transit through the overlay,
RELOAD incorporates an end-to-end reliability mechanism. When an
originating node transmits a request it MUST set a 3 second timer.
If a response has not been received when the timer fires, the
request is retransmitted with the same transaction identifier. The
request MAY be retransmitted up to 4 times (for a total of 5
messages). After the timer for the fifth transmission fires, the
message SHALL be considered to have failed. Note that this
retransmission procedure is not followed by intermediate nodes. They
follow the hop-by-hop reliability procedure described in .The above algorithm can result in multiple requests being
delivered to a node. Receiving nodes MUST generate semantically
equivalent responses to retransmissions of the same request (this
can be determined by transaction id) if the request is received
within the maximum request lifetime (15 seconds). For some requests
(e.g., FETCH) this can be accomplished merely by processing the
request again. For other requests, (e.g., STORE) it may be necessary
to maintain state for the duration of the request lifetime.When a peer sends a response to a request, it MUST construct the
destination list by reversing the order of the entries on the via
list. This has the result that the response traverses the same peers
as the request traversed, except in reverse order (symmetric
routing).RELOAD is a message-oriented request/response protocol. The
messages are encoded using binary fields. All integers are represented
in network byte order. The general philosophy behind the design was to
use Type, Length, Value fields to allow for extensibility. However,
for the parts of a structure that were required in all messages, we
just define these in a fixed position as adding a type and length for
them is unnecessary and would simply increase bandwidth and introduces
new potential for interoperability issues.Each message has three parts, concatenated as shown below:The contents of these parts are as follows: Each message has a generic header
which is used to forward the message between peers and to its
final destination. This header is the only information that an
intermediate peer (i.e., one that is not the target of a message)
needs to examine.The message being delivered
between the peers. From the perspective of the forwarding layer,
the contents is opaque, however, it is interpreted by the higher
layers.A security block containing
certificates and a digital signature over the message. Note that
this signature can be computed without parsing the message
contents. All messages MUST be signed by their originator.The following sections describe the format of each part of the
message.The structures defined in this document are defined using a
C-like syntax based on the presentation language used to define TLS.
Advantages of this style include:It is easy to write and familiar enough looking that most
readers can grasp it quickly.The ability to define nested structures allows a separation
between high-level and low level message structures.It has a straightforward wire encoding that allows quick
implementation, but the structures can be comprehended without
knowing the encoding.The ability to mechanically (compile) encoders and
decoders.This presentation is to some extent a placeholder. We consider it
an open question what the final protocol definition method and
encodings use. We expect this to be a question for the WG to
decide.Several idiosyncrasies of this language are worth noting.All lengths are denoted in bytes, not objects.Variable length values are denoted like arrays with angle
brackets."select" is used to indicate variant structures.For instance, "uint16 array<0..2^8-2>;" represents up to
254 bytes but only up to 127 values of two bytes (16 bits)
each..The following definitions are used throughout RELOAD and so are
defined here. They also provide a convenient introduction to how
to read the presentation language.An enum represents an enumerated type. The values associated
with each possibility are represented in parentheses and the
maximum value is represented as a nameless value, for purposes of
describing the width of the containing integral type. For
instance, Boolean represents a true or false:A boolean value is either a 1 or a 0 and is represented as a
single byte on the wire.The NodeId, shown below, represents a single Node-ID.A NodeId is a fixed-length 128-bit structure represented as a
series of bytes, most significant byte first. Note: the use of
"typedef" here is an extension to the TLS language, but its
meaning should be relatively obvious.A ResourceId, shown below, represents a single Resource-ID.;
]]>Like a NodeId, a Resource-ID is an opaque string of bytes, but
unlike Node-IDs, Resource-IDs are variable length, up to 255 bytes
(2048 bits) in length. On the wire, each ResourceId is preceded by
a single length byte (allowing lengths up to 255). Thus, the
3-byte value "Foo" would be encoded as: 03 46 4f 4f.A more complicated example is IpAddressPort, which represents a
network address and can be used to carry either an IPv6 or IPv4
address:The first two fields in the structure are the same no matter
what kind of address is being represented:the type of address (v4 or v6).the length of the rest of the
structure.By having the type and the length appear at the beginning of
the structure regardless of the kind of address being represented,
an implementation which does not understand new address type X can
still parse the IpAddressPort field and then discard it if it is
not needed.The rest of the IpAddressPort structure is either an
IPv4AddrPort or an IPv6AddrPort. Both of these simply consist of
an address represented as an integer and a 16-bit port. As an
example, here is the wire representation of the IPv4 address
"192.0.2.1" with port "6100".The forwarding header is defined as a ForwardingHeader structure,
as shown below.The contents of the structure are:The first four bytes identify this
message as a RELOAD message. The message is easy to demultiplex
from STUN messages by looking at the first bit. This field MUST
contain the value 0xc2454c4f (the string 'RELO' with the high
bit of the first byte set.).The 32 bit checksum/hash of the overlay
being used. The variable length string representing the overlay
name is hashed with SHA-1 and the low order 32 bits are used.
The purpose of this field is to allow nodes to participate in
multiple overlays and to detect accidental misconfiguration.
This is not a security critical function.The sequence number of the
configuration file.An 8 bit field indicating the number of
iterations, or hops, a message can experience before it is
discarded. The TTL value MUST be decremented by one at every hop
along the route the message traverses. If the TTL is 0, the
message MUST NOT be propagated further and MUST be discarded,
and a "Error_TTL_Exceeded" error should be generated. The
initial value of the TTL SHOULD be 100 unless defined otherwise
by the overlay configuration.This field is used to handle
fragmentation. The high order two bits are used to indicate the
fragmentation status: If the high bit (0x80000000) is set, it
indicates that the message is a fragment. If the next bit
(0x40000000) is set, it indicates that this is the last
fragment.The remainder of the field is used to indicate the fragment
offset. [[Open Issue: This is conceptually clear, but the
details are still lacking. Need to define the fragment offset
and total length be encoded in the header. Right now we have 14
bits reserved with the intention that they be used for
fragmenting, though additional bytes in the header might be
needed for fragmentation.]]The version of the RELOAD protocol being
used. This document describes version 0.1, with a value of
0x01.The count in bytes of the size of the
message, including the header.A unique 64 bit number that
identifies this transaction and also serves as a salt to
randomize the request and the response. Responses use the same
Transaction ID as the request they correspond to. Transaction
IDs are also used for fragment reassembly.The flags word contains control flags.
Which are ORed together. There is two currently defined flags:
ROUTE-LOG (0x1) and RESPONSE-ROUTE-LOG (0x2). These flags
indicate that the route log should be included (see .).The length of the via list in
bytes. Note that in this field and the following two length
fields we depart from the usual variable-length convention of
having the length immediately precede the value in order to make
it easier for hardware decoding engines to quickly determine the
length of the header.The length of the
destination list in bytes.The length of the route log in
bytes.The length of the header options
in bytes.The via_list contains the sequence of
destinations through which the message has passed. The via_list
starts out empty and grows as the message traverses each
peer.The destination_list contains a
sequence of destinations which the message should pass through.
The destination list is constructed by the message originator.
The first element in the destination list is where the message
goes next. The list shrinks as the message traverses each listed
peer.Contains a series of route log entries.
See .Contains a series of ForwardingOptions
entries. See .In order to be part of the overlay, a node MUST have a copy of
the overlay configuration document. In order to allow for
configuration document changes, each version of the configuration
document has a sequence number which is monotonically increasing
mod 65536. Because the sequence number may in principle wrap,
greater than or less than are interpreted by modulo arithmetic as
in TCP.When a destination node receives a request, it MUST check that
the configuration_sequence field is equal to its own configuration
sequence number. If they do not match, it MUST generate an error,
either Error_Config_Too_Old or Error_Config_Too_New. In addition,
if the configuration file in the request is too old, it MUST
generate a Config_Update message to update the requesting node.
This allows new configuration documents to propagate quickly
throughout the system. The one exception to this rule is that if
the configuration_sequence field is equal to 0xffff, and the
message type is Config_Update, then the message MUST be accepted
regardless of the receiving node's configuration sequence
number.The destination list and via lists are sequences of Destination
values:;
/* This structure may be extended with new types */
} DestinationData;
struct {
DestinationType type;
uint8 length;
DestinationData destination_data;
} Destination;
]]>This is a TLV structure with the following contents: The type of the DestinationData PDU. This may be one of
"peer", "resource", or "compressed".The length of the destination_data.The destination value itself, which is an encoded
DestinationData structure, depending on the value of
"type".This structure encodes a type, length,
value. The length field specifies the length of the
DestinationData values, which allows the addition of new
DestinationTypes. This allows an implementation which does not
understand a given DestinationType to skip over it.A DestinationData can be one of three types: A Node-ID.A compressed list of Node-IDs and/or resources. Because
this value was compressed by one of the peers, it is only
meaningful to that peer and cannot be decoded by other peers.
Thus, it is represented as an opaque string.The Resource-ID of the resource which is desired. This type
MUST only appear in the final location of a destination list
and MUST NOT appear in a via list. It is meaningless to try to
route through a resource.The route logging feature provides diagnostic information about
the path taken by the message so far and in this manner it is
similar in function to SIP's Via
header field. If the ROUTE-LOG flag is set in the Flags word, at
each hop peers MUST append a route log entry to the route log
element in the header or reject the request. The order of the
route log entry elements in the message is determined by the order
of the peers were traversed along the path. The first route log
entry corresponds to the peer at the first hop along the path, and
each subsequent entry corresponds to the peer at the next hop
along the path. If the ROUTE-LOG flag is set, the route log
entries in the request MUST be copied to the response or the
request rejected. If, and only if, the ROUTE-LOG-RESPONSE flag is
set in a request, the ROUTE-LOG flag MUST be set in the
response.Note that use of the ROUTE-LOG-RESPONSE flag means that the
response will grow on the return path, which may potentially mean
that it gets dropped due to becoming too large for some
intermediate hop. Thus, this option must be used with care.The route log is defined as follows:; /* A string */
OverlayLink linkProtocol; /* TCP or UDP */
NodeId id;
uint32 uptime;
IpAddressPort address;
opaque certificate<0..2^16-1>;
RouteLogExtension extensions<0..2^16-1>;
} RouteLogEntry;
struct {
RouteLogEntry entries<0..2^16-1>;
} RouteLog;
]]>The route log consists of an arbitrary number of RouteLogEntry
values, each representing one node through which the message has
passed.Each RouteLogEntry consists of the following values:A textual representation of the software versionThe Overlay Link Layer protocol, currently either "tcp_tls"
or "udp_dtls".The Node-ID of the peer.The uptime of the peer in seconds.The address and port of the peer.The peer's certificate. Note that this may be omitted by
setting the length to zero.Extensions, if any.Extensions are defined using a RouteLogExtension structure. New
extensions are defined by defining a new code point for
RouteLogExtensionType and adding a new arm to the
RouteLogExtension structure. The contents of that structure
are:The type of the extension.The length of the rest of the structure.The extension value.The Forwarding header can be extended with forwarding header
options, which are a series of ForwardingOptions structures:Each ForwardingOption consists of the following values:The type of the option.The length of the rest of the structure.Three flags are defined FORWARD_CRITICAL(0x01),
DESTINATION_CRITICAL(0x02), and RESPONSE_COPY(0x04). These
flags MUST NOT be set in a response. If the FORWARD_CRITICAL
flag is set, any node that would forward the message but does
not understand this options MUST reject the request with an
757 error response. If the DESTINATION_CRITICAL flag is set,
any node generates a response to the message but does not
understand the forwarding option MUST reject the request with
an 757 error response. If the RESPONSE_COPY flag is set, any
node generating a response MUST copy the option from the
request to the response and clear the RESPONSE_COPY,
FORWARD_CRITICAL and DESTINATION_CRITICAL flags.The option value.The second major part of a RELOAD message is the contents part,
which is defined by MessageContents:;
} MessageContents;
]]>The contents of this structure are as follows: This indicates the message that is being sent. The code space
is broken up as follows. ReservedRequests and responses. These code
points are always paired, with requests being odd and the
corresponding response being the request code plus 1. Thus,
"probe_request" (the Probe request) has value 1 and
"probe_answer" (the Probe response) has value 2ErrorThe message body itself, represented as a variable-length
string of bytes. The bytes themselves are dependent on the code
value. See the sections describing the various RELOAD methods
(Join, Update, Attach, Store, Fetch, etc.) for the definitions
of the payload contents.A peer processing a request returns its status in the
message_code field. If the request was a success, then the message
code is the response code that matches the request (i.e., the next
code up). The response payload is then as defined in the
request/response descriptions.If the request failed, then the message code is set to 0xffff
(error) and the payload MUST be an error_response PDU, as shown
below.When the message code is 0xffff, the payload MUST be an
ErrorResponse.;
} ErrorResponse;
]]>The contents of this structure are as follows:A numeric error code indicating the error that
occurred.An arbitrary byte string. Unless otherwise specified,
this will be a text string providing further information
about what went wrong.The following error code values are defined. The numeric values
for these are defined in .The requesting peer needs to
sign and provide a certificate. [[TODO: The semantics here
don't seem quite right.]]The requesting peer does not
have permission to make this request.The resource or peer cannot be
found or does not exist.A response to the request
has not been received in a suitable amount of time. The
requesting peer MAY resend the request at a later time.A request can't be
completed because some precondition was incorrect. For
instance, the wrong generation counter was providedA peer
receiving the request is using a different overlay, overlay
algorithm, or hash algorithm.A peer
receiving the request with a forwarding options flagged as
critical but the peer does not support this option. See
section .A peer receiving the request
where the TTL got decremented to zero. See section .A peer receiving the
request that was too large. See section .A destination peer
received a request with a configuration sequence that's too
old.A destination node
received a request with a configuration sequence that's too
new. A node which receives this error MUST generate a
Config_Update message to send a new copy of the configuration
document to the node which generated the error.The third part of a RELOAD message is the security block. The
security block is represented by a SecurityBlock structure:;
} GenericCertificate;
struct {
GenericCertificate certificates<0..2^16-1>;
Signature signature;
} SecurityBlock;
]]>The contents of this structure are:A bucket of certificates.A signature over the message contents.The certificates bucket SHOULD contain all certificates necessary
to verify every signature in both the message and the internal
message objects. This is the only location in the message which
contains certificates, thus allowing for only a single copy of each
certificate. In systems which have some alternate certificate
distribution mechanism, some certificates MAY be omitted. However,
implementors should note that this creates the possibility that
messages may not be immediately verifiable upon receipt of the
certificates must first be retrieved.Each certificate is represented by a GenericCertificate
structure, which has the following contents:The type of the certificate. Only one type is defined: x509
representing an X.509 certificateThe encoded version of the certificate. For X.509
certificates, it is the DER form.The signature is computed over the payload and parts of
forwarding header. The payload, in case of a Store, may contain an
additional signature computed over a StoreReq structure. All
signatures are formatted using the Signature element. This element
is also used in other contexts where signatures are needed. The
input structure to the signature computation varies depending on the
data element being signed.;
/* This structure may be extended with new types if necessary*/
} SignerIdentityValue;
struct {
SignerIdentityType identity_type;
uint16 length;
SignerIdentityValue identity[SignerIdentity.length];
} SignerIdentity;
struct {
SignatureAndHashAlgorithm algorithm;
SignerIdentity identity;
opaque signature_value<0..2^16-1>;
} Signature;
]]>The signature construct contains the following values:The signature algorithm in use. The algorithm definitions are
found in the IANA TLS SignatureAlgorithm Registry.The identity used to form the signatureThe value of the signatureThe only currently permitted identity format is a hash of the
signer's certificate. The hash_alg field is used to indicate the
algorithm used to produce the hash. The certificate_hash contains
the hash of the certificate object as represented in the
certificates structure. The SignerIdentity structure is typed purely
to allow for future (unanticipated) extensibility. [TODO: Should we
remove this extensibility point?]For signatures over messages the input to the signature is
computed over:overlay + transaction_id + MessageContents +
SignerIdentityWhere overlay and transaction_id come from the forwarding header
and + indicates concatenation.[[TODO: Check the inputs to this carefully.]]The input to signatures over data values is different, and is
described in .All RELOAD messages MUST be signed. Upon receipt, the receiving
node MUST verify the signature and the authorizing certificate. This
check provides a minimal level of assurance that the sending node is
a valid part of the overlay as well as cryptographic authentication
of the sending node. In addition, responses MUST be checked as
follows:The response to a message sent to a specific Node-Id MUST
have been sent by that Node-Id.The response to a message sent to a Resource-Id MUST have
been sent by a Node-Id which is as close to or closer to the
target Resource-Id than any node in the requesting node's
neighbor table.The second condition serves as a primitive check for responses
from wildly wrong nodes but is not a complete check. Note that in
periods of churn, it is possible for the requesting node to obtain a
closer neighbor while the request is outstanding. This will cause
the response to be rejected and the request to be retransmitted.In addition, some methods (especially Store) have additional
authentication requirements, which are described in the sections
covering those methods.As discussed in previous sections, RELOAD does not itself implement
any overlay topology. Rather, it relies on Topology Plugins, which
allow a variety of overlay algorithms to be used while maintaining the
same RELOAD core. This section describes the requirements for new
topology plugins and the methods that RELOAD provides for overlay
topology maintenance.When specifying a new overlay algorithm, at least the following
need to be described:Joining procedures, including the contents of the Join
message.Stabilization procedures, including the contents of the
Update message, the frequency of topology probes and keepalives,
and the mechanism used to detect when peers have
disconnected.Exit procedures, including the contents of the Leave
message.The length of the Resource-IDs and Node-IDs. For DHTs, the
hash algorithm to compute the hash of an identifier.The procedures that peers use to route messages.The replication strategy used to ensure data redundancy.This section describes the methods that topology plugins use to
join, leave, and maintain the overlay.A new peer (but which already has credentials) uses the JoinReq
message to join the overlay. The JoinReq is sent to the
responsible peer depending on the routing mechanism described in
the topology plugin. This notifies the responsible peer that the
new peer is taking over some of the overlay and it needs to
synchronize its state.;
} JoinReq;
]]>The minimal JoinReq contains only the Node-ID which the sending
peer wishes to assume. Overlay algorithms MAY specify other data
to appear in this request.If the request succeeds, the responding peer responds with a
JoinAns message, as defined below:;
} JoinAns;
]]>If the request succeeds, the responding peer MUST follow up by
executing the right sequence of Stores and Updates to transfer the
appropriate section of the overlay space to the joining peer. In
addition, overlay algorithms MAY define data to appear in the
response payload that provides additional info.In general, nodes which cannot form connections SHOULD report
an error. However, implementations MUST provide some mechanism
whereby nodes can determine they are potentially the first node
and take responsibility for the overlay. This specification does
not mandate any particular mechanism, but a configuration flag or
setting seems appropriate.The LeaveReq message is used to indicate that a node is exiting
the overlay. A node SHOULD send this message to each peer with
which it is directly connected prior to exiting the overlay.;
} LeaveReq;
]]>LeaveReq contains only the Node-ID of the leaving peer. Overlay
algorithms MAY specify other data to appear in this request.Upon receiving a Leave request, a peer MUST update its own
routing table, and send the appropriate Store/Update sequences to
re-stabilize the overlay.Update is the primary overlay-specific maintenance message. It
is used by the sender to notify the recipient of the sender's view
of the current state of the overlay (its routing state) and it is
up to the recipient to take whatever actions are appropriate to
deal with the state change.The contents of the UpdateReq message are completely
overlay-specific. The UpdateAns response is expected to be either
success or an error.The Route_Query request allows the sender to ask a peer where
they would route a message directed to a given destination. In
other words, a RouteQuery for a destination X requests the Node-ID
where the receiving peer would next route to get to X. A
RouteQuery can also request that the receiving peer initiate an
Update request to transfer his routing table.One important use of the RouteQuery request is to support
iterative routing. The sender selects one of the peers in its
routing table and sends it a RouteQuery message with the
destination_object set to the Node-ID or Resource-ID it wishes to
route to. The receiving peer responds with information about the
peers to which the request would be routed. The sending peer MAY
then Attaches to that peer(s), and repeats the RouteQuery.
Eventually, the sender gets a response from a peer that is closest
to the identifier in the destination_object as determined by the
topology plugin. At that point, the sender can send messages
directly to that peer.A RouteQueryReq message indicates the peer or resource that
the requesting peer is interested in. It also contains a
"send_update" option allowing the requesting peer to request a
full copy of the other peer's routing table.;
} RouteQueryReq;
]]>The contents of the RouteQueryReq message are as follows:A single byte. This may be set to "true" to indicate that
the requester wishes the responder to initiate an Update
request immediately. Otherwise, this value MUST be set to
"false".The destination which the requester is interested in.
This may be any valid destination object, including a
Node-ID, compressed ids, or Resource-ID.Other data as appropriate for the overlay.A response to a successful RouteQueryReq request is a
RouteQueryAns message. This is completely overlay specific.Probe provides a number of primitive "exploration" services:
(1) it allows node to determine which resources another node is
responsible for (2) it allows some discovery services in multicast
settings. A probe can be addressed to a specific Node-ID, or the
peer controlling a given location (by using a resource ID). In
either case, the target Node-IDs respond with a simple response
containing some status information.The ProbeReq message contains a list (potentially empty) of
the pieces of status information that the requester would like
the responder to provide.;
} ProbeReq
]]>The two currently defined values for ProbeInformation
are:indicates that the peer should Respond with the fraction
of the overlay for which the responding peer is
responsible.indicates that the peer should Respond with the number of
resources currently being stored by the peer.A successful ProbeAns response contains the information
elements requested by the peer.;
} ProbeAns;
]]>A ProbeAns message contains the following elements: A sequence of ProbeInformation structures, as shown
below.Each of the current possible Probe information types is a
32-bit unsigned integer. For type "responsible_ppb", it is the
fraction of the overlay for which the peer is responsible in
parts per billion. For type "num_resources", it is the number of
resources the peer is storing.The responding peer SHOULD include any values that the
requesting peer requested and that it recognizes. They SHOULD be
returned in the requested order. Any other values MUST NOT be
returned.Each node maintains connections to a set of other nodes defined by
the topology plugin. This section defines the methods RELOAD uses to
form and maintain connections between nodes in the overlay. Three
methods are defined:used to form connections between nodes.
When node A wants to connect to node B, it sends an Attach message
to node B through the overlay. The Attach contains A's ICE
parameters. B responds with its ICE parameters and the two nodes
perform ICE to form connection.like attach, it is used to form
connections between nodes but instead of using full ICE, it only
uses a subset known as ICE-Lite.is a simple request/response which is used to
verify connectivity of the target peer.A node sends an Attach request when it wishes to establish a
direct TCP or UDP connection to another node for the purposes of
sending RELOAD messages or application layer protocol messages, such
as SIP.As described in , an
Attach may be routed to either a Node-ID or to a Resource-ID. An
Attach routed to a specific Node-ID will fail if that node is not
reached. An Attach routed to a Resource-ID will establish a
connection with the peer currently responsible for that Resource-ID,
which may be useful in establishing a direct connection to the
responsible peer for use with frequent or large resource
updates.An Attach in and of itself does not result in updating the
routing table of either node. That function is performed by Updates.
If node A has Attached to node B, but not received any Updates from
B, it MAY route messages which are directly addressed to B through
that channel but MUST NOT route messages through B to other peers
via that channel. The process of Attaching is separate from the
process of becoming a peer (using Update) to prevent half-open
states where a node has started to form connections but is not
really ready to act as a peer.An AttachReq message contains the requesting peer's ICE
connection parameters formatted into a binary structure.;
struct {
opaque ufrag<0..2^8-1>;
opaque password<0..2^8-1>;
uint16 application;
opaque role<0..2^8-1>;
IceCandidate candidates<0..2^16-1>;
} AttachReqAns;
]]>The values contained in AttachReq and AttachAns are: The username fragment (from ICE)The ICE password.A 16-bit port number. This port number represents the IANA
registered port of the protocol that is going to be sent on
this connection. For SIP, this is 5060 or 5061, and for RELOAD
is TBD. By using the IANA registered port, we avoid the need
for an additional registry and allow RELOAD to be used to set
up connections for any existing or future application
protocol.An active/passive/actpass attribute from RFC 4145 .One or more ICE candidate values in the string
representation used in ordinary ICE. [[OPEN ISSUE: This is
convenient for stacks, but unaesthetic.]] Each candidate has
an IP address, IP address family, port, transport protocol,
priority, foundation, component ID, STUN type and related
address. The candidate_list is a list of string candidate
values from ICE.These values should be generated using the procedures described
in .If a peer receives an Attach request, it SHOULD follow the
process the request and generate its own response with a
AttachReqAns. It should then begin ICE checks. When a peer
receives an Attach response, it SHOULD parse the response and
begin its own ICE checks.This section describes the profile of ICE that is used with
RELOAD. RELOAD implementations MUST implement full ICE. Because
RELOAD always tries to use TCP and then UDP as a fallback, there
will be multiple candidates of the same IP version, which requires
full ICE.In ICE as defined by , SDP is used to carry the ICE
parameters. In RELOAD, this function is performed by a binary
encoding in the Attach method. This encoding is more restricted
than the SDP encoding because the RELOAD environment is
simpler:Only a single media stream is supported.In this case, the "stream" refers not to RTP or other types
of media, but rather to a connection for RELOAD itself or for
SIP signaling.RELOAD only allows for a single offer/answer exchange.
Unlike the usage of ICE within SIP, there is never a need to
send a subsequent offer to update the default candidates to
match the ones selected by ICE.An agent follows the ICE specification as described in and with the changes and
additional procedures described in the subsections below.ICE relies on the node having one or more STUN servers to use.
In conventional ICE, it is assumed that nodes are configured with
one or more STUN servers through some out-of-band mechanism. This
is still possible in RELOAD but RELOAD also learns STUN servers as
it connects to other peers. Because all RELOAD peers implement ICE
and use STUN keepalives, every peer is a STUN server . Accordingly, any peer a node knows will
be willing to be a STUN server -- though of course it may be
behind a NAT.A peer on a well-provisioned wide-area overlay will be
configured with one or more bootstrap peers. These peers make an
initial list of STUN servers. However, as the peer forms
connections with additional peers, it builds more peers it can use
as STUN servers.Because complicated NAT topologies are possible, a peer may
need more than one STUN server. Specifically, a peer that is
behind a single NAT will typically observe only two IP addresses
in its STUN checks: its local address and its server reflexive
address from a STUN server outside its NAT. However, if there are
more NATs involved, it may discover that it learns additional
server reflexive addresses (which vary based on where in the
topology the STUN server is). To maximize the chance of achieving
a direct connection, a peer SHOULD group other peers by the
peer-reflexive addresses it discovers through them. It SHOULD then
select one peer from each group to use as a STUN server for future
connections.Only peers to which the peer currently has connections may be
used. If the connection to that host is lost, it MUST be removed
from the list of stun servers and a new server from the same group
SHOULD be selected.When a node wishes to establish a connection for the purposes
of RELOAD signaling or SIP signaling (or any other application
protocol for that matter), it follows the process of gathering
candidates as described in Section 4 of ICE . RELOAD utilizes a single
component, as does SIP. Consequently, gathering for these
"streams" requires a single component.An agent MUST implement ICE-tcp , and MUST gather at least one
UDP and one TCP host candidate for RELOAD and for SIP.The ICE specification assumes that an ICE agent is configured
with, or somehow knows of, TURN and STUN servers. RELOAD provides
a way for an agent to learn these by querying the overlay, as
described in and .The agent SHOULD prioritize its TCP-based candidates over its
UDP-based candidates in the prioritization described in Section
4.1.2 of ICE .The default candidate selection described in Section 4.1.3 of
ICE is ignored; defaults are not signaled or utilized by
RELOAD.Section 4.3 of ICE describes procedures for encoding the SDP
for conveying RELOAD or SIP ICE candidates. Instead of actually
encoding an SDP, the candidate information (IP address and port
and transport protocol, priority, foundation, component ID, type
and related address) is carried within the attributes of the
Attach request or its response. Similarly, the username fragment
and password are carried in the Attach message or its response.
describes the detailed
attribute encoding for Attach. The Attach request and its response
do not contain any default candidates or the ice-lite attribute,
as these features of ICE are not used by RELOAD. The Attach
request and its response also contain a application attribute,
with a value of SIP or RELOAD, which indicates what protocol is to
be run over the connection. The RELOAD Attach request MUST only be
utilized to set up connections for application protocols that can
be multiplexed with STUN.Since the Attach request contains the candidate information and
short term credentials, it is considered as an offer for a single
media stream that happens to be encoded in a format different than
SDP, but is otherwise considered a valid offer for the purposes of
following the ICE specification. Similarly, the Attach response is
considered a valid answer for the purposes of following the ICE
specification.An agent MUST skip the verification procedures in Section 5.1
and 6.1 of ICE. Since RELOAD requires full ICE from all agents,
this check is not required.The roles of controlling and controlled as described in Section
5.2 of ICE are still utilized with RELOAD. However, the offerer
(the entity sending the Attach request) will always be
controlling, and the answerer (the entity sending the Attach
response) will always be controlled. The connectivity checks MUST
still contain the ICE-CONTROLLED and ICE-CONTROLLING attributes,
however, even though the role reversal capability for which they
are defined will never be needed with RELOAD. This is to allow for
a common codebase between ICE for RELOAD and ICE for SDP.The processes of forming check lists in Section 5.7 of ICE,
scheduling checks in Section 5.8, and checking connectivity checks
in Section 7 are used with RELOAD without change.The controlling agent MUST utilize regular nomination. This is
to ensure consistent state on the final selected pairs without the
need for an updated offer, as RELOAD does not generate additional
offer/answer exchanges.The procedures in Section 8 of ICE are followed to conclude
ICE, with the following exceptions:The controlling agent MUST NOT attempt to send an updated
offer once the state of its single media stream reaches
Completed.Once the state of ICE reaches Completed, the agent can
immediately free all unused candidates. This is because RELOAD
does not have the concept of forking, and thus the three
second delay in Section 8.3 of ICE does not apply.An agent MUST NOT send a subsequent offer or answer. Thus, the
procedures in Section 9 of ICE MUST be ignored.STUN MUST be utilized for the keepalives described in Section
10 of ICE. [[ TODO - this does not define what happens for TCP
]]The procedures of Section 11 apply to RELOAD as well. However,
in this case, the "media" takes the form of application layer
protocols (RELOAD or SIP for example) over TLS or DTLS.
Consequently, once ICE processing completes, the agent will begin
TLS or DTLS procedures to establish a secure connection. The node
which sent the Attach request MUST be the TLS server. The other
node MUST be the TLS client. The nodes MUST verify that the
certificate presented in the handshake matches the identity of the
other peer as found in the Attach message. Once the TLS or DTLS
signaling is complete, the application protocol is free to use the
connection.The concept of a previous selected pair for a component does
not apply to RELOAD, since ICE restarts are not possible with
RELOAD.An agent MUST be prepared to receive packets for the
application protocol (TLS or DTLS carrying RELOAD, SIP or anything
else) at any time. The jitter and RTP considerations in Section 11
of ICE do not apply to RELOAD or SIP.An alternative to using the full ICE supported by the Attach
request is to use ICE-Lite with the AttachLite request. This will
not work in all of the scenarios where ICE would work, but in some
cases, particularly those with no NATs or firewalls, it will work.
Configuration for the overlay indicates if this can be used or
not.OPEN ISSUE: We originally envisioned adding support for ICE-Lite
directly to the regular Attach method. However, we found that both
the parameters and processing were completely different, resulting
in almost no overlap between the two methods. Therefore we chose to
separate this out for overlays where the complexities of ICE are not
needed. Note that it is still possible for a node with a public
unfiltered address intending to interoperate to implement Attach
without the candidate gathering phases of ICE and achieve
essentially the same result. If simpler behavior or a better
encoding of ICE-Lite in Attach is developed, such an approach would
be preferable.An AttachLiteReq message contains the requesting peer's
ICE-Lite connection parameters formatted into a binary structure.
When using the AttachLite request, both sides act as ICE-Lite
hosts.;
} AttachLiteReqs;
]]>The values contained in AttachLiteReq are: A 16-bit port number used in the same was as in the Attach
request. This port number represents the IANA registered port
of the protocol that is going to be sent on this
connection.One or more ICE candidate values. Each one contains an IP
address and family, transport protocol, and port to connect to
as well as a priority.These values should be generated using the procedures described
in .STUN is not used for connectivity checks when doing ICE-Lite,
instead the DTLS or TLS handshake forms the connectivity check.
The host that received the AttachLiteReq MUST initiate TLS or DTLS
connections to candidates provided in the request. When a
connection forms, the node MUST check the certificate is for the
node that send AttachLiteReq and if is not, MUST close the
connection.Since TLS provides the connectivity check, there is no need for
the RFC 4571 style framing shim for
STUN when using TLS and this is not used for this protocol.This is a non normative section to help implementors.At times ICE can seem a bit daunting to gets one head around.
For a simple IPv4 only peer, a simple implementation of
Attach-Lite could be done be doing the following: When sending an AttachLiteReq, form one with a candidate
with a priority value of
(2^24)*(126)+(2^8)*(65535)+(2^0)*(256-1) that specifies the
UDP port being listened to and another one with the TCP
port.When receiving an AttachLiteReq, try to form a connection
to each candidate in the request. Check the certificate
receive in the TLS handshake has the correct Node-ID as the
node that send the AttchLiteReq. If multiple connection
succeed, close all but the one with highest priority.Do normal TLS and DTLS with no need for any special framing
or STUN processing.Ping is used to test connectivity along a path. A ping can be
addressed to a specific Node-ID, the peer controlling a given
location (by using a resource ID), or to the broadcast Node-ID (all
1s).A successful PingAns response contains the information elements
requested by the peer.A PingAns message contains the following elements: A randomly generated 64-bit response ID. This is used to
distinguish Ping responses in cases where the Ping request is
multicast.The time when the ping responses was created in absolute
time, represented in milliseconds since midnight Jan 1, 1970
which is the UNIX epoch.The Config_Update method is used to propagate updated
configuration files across the overlay. Whenever a node detects that
another node has an old configuration file, it MUST generate a
Config_Update request.;
} Config_UpdateReq;
]]>The Config_UpdateReq message contains the following elements:
The contents of the configuration document.The Config_UpdateReq should only be processed if all the
following are true: The configuration sequence number in the document is
greater than the current configuration sequence number.The configuration document is correctly digitally signed
(see for details on
signatures. Otherwise appropriate errors MUST be generated.If the document is acceptable, then the node MUST reconfigure
itself to match the new document. This may include adding
permissions for new kinds, deleting old kinds, or even, in extreme
circumstances, exiting and reentering the overlay, if, for
instance, the DHT algorithm has changed.The response for Config_Update is empty.RELOAD can use multiple Overlay Link protocols to send its
messages. Because ICE is used to establish connections (see ), RELOAD nodes are able to detect
which Overlay Link protocols are offered by other nodes and establish
connections between each other. Any link protocol needs to be able to
establish a secure, authenticated connection, and provide data origin
authentication and message integrity for individual data elements.
RELOAD currently supports two Overlay Link protocols:TLS over TCPDTLS over UDPNote that although UDP does not properly have "connections", both
TLS and DTLS have a handshake which establishes a stateful
association, a similar stateful construct, and we simply refer to
these as "connections" for the purposes of this document.If a peer receives a message that is larger than value of
max-message-size defined in the overlay configuration, the peer SHOULD
send an Error_Message_Too_Large error then close the TLS or DTLS
session from which the message was received. Note that this error can
be sent and the session closed before receiving the complete message.
If the forwarding header is larger than the max-message-size, the
receiver SHOULD close the TLS or DTLS session without sending an
error.The P2PSIP Working Group has expressed interest in supporting a
HIP-based link protocol. Such support would require specifying such
details as:How to issue certificates which provided identities
meaningful to the HIP base exchange. We anticipate that this
would require a mapping between ORCHIDs and NodeIds.How to carry the HIP I1 and I2 messages. We anticipate that
this would require defining a HIP Tunnel usage.How to carry RELOAD messages over HIP.We leave this work as a topic for another draft.When RELOAD is carried over DTLS or another unreliable link
protocol, it needs to be used with a reliability and congestion
control mechanism, which is provided on a hop-by-hop basis, matching
the semantics if TCP were used. The basic principle is that each
message, regardless of if it carries a request or responses, will
get an ACK and be reliably retransmitted. The receiver's job is very
simple, limited to just sending ACKs. All the complexity is at the
sender side. This allows the sending implementation to trade off
performance versus implementation complexity without affecting the
wire protocol.In order to support unreliable links, each message is wrapped in
a very simple framing layer (FramedMessage) which is only used for
each hop. This layer contains a sequence number which can then be
used for ACKs.[[TODO: There had been discussion of always using this,
but it's tied up in the rest of the reliability questions.]]The definition of FramedMessage is:;
case ack:
uint32 ack_sequence;
uint32 received;
};
} FramedMessage;
]]>The type field of the PDU is set to indicate whether the
message is data or an acknowledgement. Note that these values have
been set to force the first bit to be high, thus allowing easy
demultiplexing with STUN. All FramedMessageType values must be
> 128.If the message is of type "data", then the remainder of the PDU
is as follows: the sequence numberthe message that is being transmitted.Each connection has it own sequence number space. Initially the
value is zero and it increments by exactly one for each message
sent over that connection.When the receiver receive a message, it SHOULD immediately send
an ACK message. The receiver MUST keep track of the 32 most recent
sequence numbers received on this association in order to generate
the appropriate ack.If the PDU is of type "ack", the contents are as follows: The sequence number of the message being acknowledged.A bitmask indicating is each of the previous 32 sequence
numbers before this packet had been received as one of the
most recently received 32 packets on this connection. When a
packet is received with a sequence number N, the receiver
looks at the sequence number of the previously 32 packets
received on this connection,. Call the previously received
packet number M. And for each of the previous 32 packets, if
the sequence number M is less than N but greater than N-32,
the N-M bit of the received bitmask is set to one otherwise it
is zero.Note that a bit being set indicates a particular packet was
received but if the bit is set to zero it only means it is
unknown if it was received or not. It might have been received
but not in the 32 most recently received window.The received field bits in the ACK provide a very high degree
of redundancy for the sender to figure out which packets the
receiver received and can then estimate packet loss rates. If the
sender also keeps track of the time at which recent sequence
numbers were sent, the RTT can be estimated.Because the receiver's role is limited to providing packet
acknowledgements, a wide variety of congestion control algorithms
can be implemented on the sender side while using the same basic
wire protocol. Senders MUST implement a retransmission and
congestion control scheme no more aggressive then TFRC. One way to do that is for senders to
implement TFRC-SP and use the
received bitmask to allow the sender to compute packet loss event
rates.An algorithm which will not perform as well as TFRC-SP but is
easy to implement is described in this section and can be used
if implementations don't use a more advanced techniques such as
TFRC-SP.A peer SHOULD retransmit a message if it has not received an
ACK for that messages starting with an interval of RTO
("Retransmission TimeOut"), doubling after each retransmission.
In each retransmission, the sequence number is incremented. The
RTO is an estimate of the round-trip time (RTT), and is computed
as described in RFC 2988 [RFC2988], with two exceptions. First,
the initial value for RTO SHOULD be configurable (rather than
the 3 s recommended in RFC 2988) and SHOULD be equal to or
greater than 500 ms. The exception cases for this "SHOULD" are
when other mechanisms are used to derive congestion thresholds,
or when this is used in non- Internet environments with known
network capacities. In fixed-line access links, a value of 500
ms is RECOMMENDED. Second, the value of RTO SHOULD NOT be
rounded up to the nearest second. Rather, a 1 ms accuracy SHOULD
be maintained. As with TCP, the usage of Karn's algorithm is
RECOMMENDED [TODO REF KARN87] which means that RTT estimates
SHOULD NOT be computed from transactions that result in the
retransmission of a request. The value for RTO is calculated
separately for each DTLS session.Retransmissions continue until a response is received, or
until a total of 5 requests have been sent or there has been a
hard ICMP error [RFC1122]. The receiver knows a responses was
received by receiving and ACK with a sequence number that
indicates it is a response to one of the transmissions of this
messages. For example, assuming an RTO of 500 ms, requests would
be sent at times 0 ms, 500 ms, 1500 ms, 3500 ms, and 7500 ms. If
all retransmissions for a message fail, the DTLS connection
SHOULD be closed.Once an ACK has been received for a message, the next
messages can be sent but the peer SHOULD ensure that there is at
least 10 ms between sending any two messages.In order to allow transmission over datagram protocols such as
DTLS, RELOAD messages may be fragmented. If a message is too large
for a peer to transmit to the next peer it MUST fragment the
message. Note that this implies that intermediate peers may
re-fragment messages if the incoming and outgoing paths have
different maximum datagram sizes. Intermediate peers SHOULD NOT
reassemble fragments.When a message is fragmented, each fragment has a full copy of
the forwarding header but the rest of the messages is split across
the fragments. The fragment offset value is stored in the lower 24
bits of the fragment field of the forwarding header. The offset is
the number of bytes of the start of data from the end of the
forwarding header so the first fragment has an offset of 0. The
first and last bit indicators MUST be appropriately set. If the
message is not fragmented, then both the first and last fragment are
set to 1 and the offset is 0 resulting in a fragment value of
0xC0000000.TODO - discuss how to size fragments to leave room for expansion
of forwarding header. Open Issue: Remove route log?Upon receipt of a fragmented message by the intended peer, the
peer holds the fragments in a holding buffer until the entire
message has been received. The message is then reassembled into a
single message and processed. In order to mitigate denial of service
attacks, receivers SHOULD time out incomplete fragments after 15
seconds. Note the 15 seconds was derived from looking at the end to
end retransmission time and saving fragments long enough for the
full end to end retransmissions to take place. Ideally the receiver
would have enough buffer space to deal with storing 15 seconds worth
of fragments at whatever rate it receives messages on it89s
interfaces, however, if the receiver runs out of buffer space to
reassemble the messages it SHOULD close the DTLS session.RELOAD provides a set of generic mechanisms for storing and
retrieving data in the Overlay Instance. These mechanisms can be used
for new applications simply by defining new code points and a small set
of rules. No new protocol mechanisms are required.The basic unit of stored data is a single StoredData structure:The contents of this structure are as follows: The length of the rest of the structure in octets.The time when the data was stored in absolute time, represented
in milliseconds since the Unix epoch of midnight Jan 1, 1970. Any
attempt to store a data value with a storage time before that of a
value already stored at this location MUST generate a
Error_Data_Too_Old error. This prevents rollback attacks. Note that
this does not require synchronized clocks: the receiving peer uses
the storage time in the previous store, not its own clock.The validity period for the data, in seconds, starting from the
time of store.The data value itself, as described in .A signature over the data value. describes the signature computation.
The element is formatted as described in Each Resource-ID specifies a single location in the Overlay Instance.
However, each location may contain multiple StoredData values
distinguished by Kind-ID. The definition of a kind describes both the
data values which may be stored and the data model of the data. Some
data models allow multiple values to be stored under the same Kind-ID.
Section describes the available
data models. Thus, for instance, a given Resource-ID might contain a
single-value element stored under Kind-ID X and an array containing
multiple values stored under Kind-ID Y.Each StoredData element is individually signed. However, the
signature also must be self-contained and cover the Kind-ID and
Resource-ID even though they are not present in the StoredData
structure. The input to the signature algorithm is:resource_id + kind + StoredDataWhere these values are: The resource ID where this data is stored.The Kind-ID for this data.The contents of the stored data value, as described in the
previous sections, with the lifetime set to 0.[OPEN ISSUE: Should we include the identity in the string that
forms the input to the signature algorithm?.]Once the signature has been computed, the signature is represented
using a signature element, as described in .The protocol currently defines the following data models:single valuearraydictionaryThese are represented with the StoredDataValue structure:;
} DataValue;
struct {
DataModel model;
select (model) {
case single_value:
DataValue single_value_entry;
case array:
ArrayEntry array_entry;
case dictionary:
DictionaryEntry dictionary_entry;
/* This structure may be extended */
} ;
} StoredDataValue;
]]>We now discuss the properties of each data model in turn:A single-value element is a simple, opaque sequence of bytes.
There may be only one single-value element for each Resource-ID,
Kind-ID pair.A single value element is represented as a DataValue, which
contains the following two elements:This value indicates whether the value exists at all. If it
is set to False, it means that no value is present. If it is
True, that means that a value is present. This gives the
protocol a mechanism for indicating nonexistence as opposed to
emptiness.The stored data.An array is a set of opaque values addressed by an integer index.
Arrays are zero based. Note that arrays can be sparse. For instance,
a Store of "X" at index 2 in an empty array produces an array with
the values [ NA, NA, "X"]. Future attempts to fetch elements at
index 0 or 1 will return values with "exists" set to False.A array element is represented as an ArrayEntry:The contents of this structure are: The index of the data element in the array.The stored data.A dictionary is a set of opaque values indexed by an opaque key
with one value for each key. A single dictionary entry is
represented as followsA dictionary element is represented as a DictionaryEntry:;
struct {
DictionaryKey key;
DataValue value;
} DictionaryEntry;
]]>The contents of this structure are: The dictionary key for this value.The stored data.Every kind which is storable in an overlay MUST be associated with
an access control policy. This policy defines whether a request from a
given node to operate on a given value should succeed or fail. It is
anticipated that only a small number of generic access control
policies are required. To that end, this section describes a small set
of such policies and
establishes a registry for new policies if required. Each policy has a
short string identifier which is used to reference it in the
configuration document.In the USER-MATCH policy, a given value MUST be written (or
overwritten) if and only if the request is signed with a key
associated with a certificate whose user name hashes (using the hash
function for the overlay) to the Resource-ID for the resource.
Recall that the certificate may, depending on the overlay
configuration, be self-signed.In the NODE-MATCH policy, a given value MUST be written (or
overwritten) if and only if the request is signed with a key
associated with a certificate whose Node-ID hashes (using the hash
function for the overlay) to the Resource-ID for the resource.The USER-NODE-MATCH policy may only be used with dictionary
types. In the USER-NODE-MATCH policy, a given value MUST be written
(or overwritten) if and only if the request is signed with a key
associated with a certificate whose user name hashes (using the hash
function for the overlay) to the Resource-ID for the resource. In
addition, the dictionary key MUST be equal to the Node-ID in the
certificate.In the NODE-MULTIPLE policy, a given value MUST be written (or
overwritten) if and only if the request is signed with a key
associated with a certificate containing a Node-ID such that
H(Node-ID || i) is equal to the Resource-ID for some small integer
value if i. When this policy is in use, the maximum value of i MUST
be specified, typically in the configuration document.The USER-MATCH-WITH-ANONYMOUS-CREATE policy is like the
USER-MATCH policy except that any user MAY create a new value in a
given location. However, only a user matching the USER-MATCH
criteria may overwrite an existing value. This allows the creation
of an anonymous "drop box" which may be useful for applications like
voice mail.RELOAD provides several methods for storing and retrieving
data:Store values in the overlayFetch values from the overlayFind the values stored at an individual peerThese methods are each described in the following sections.The Store method is used to store data in the overlay. The format
of the Store request depends on the data model which is determined
by the kind.A StoreReq message is a sequence of StoreKindData values, each
of which represents a sequence of stored values for a given kind.
The same Kind-ID MUST NOT be used twice in a given store request.
Each value is then processed in turn. These operations MUST be
atomic. If any operation fails, the state MUST be rolled back to
before the request was received.The store request is defined by the StoreReq structure:;
} StoreKindData;
struct {
ResourceId resource;
uint8 replica_number;
StoreKindData kind_data<0..2^32-1>;
} StoreReq;
]]>A single Store request stores data of a number of kinds to a
single resource location. The contents of the structure are: The resource to store at.The number of this replica. When a storing peer saves
replicas to other peers each peer is assigned a replica number
starting from 1 and sent in the Store message. This field is
set to 0 when a node is storing its own data. This allows
peers to distinguish replica writes from original writes.A series of elements, one for each kind of data to be
stored.If the replica number is zero, then the peer MUST check that it
is responsible for the resource and if not reject the request. If
the replica number is nonzero, then the peer MUST check that it
expects to be a replica for the resource and that the request
sender is consistent with being the responsible node (i.e., that
the receiving peer does not know of a better node) and if not
reject the request.Each StoreKindData element represents the data to be stored for
a single Kind-ID. The contents of the element are: The Kind-ID. Implementations SHOULD reject requests
corresponding to unknown kinds unless specifically configured
otherwise.The data model of the data. The kind defines what this has
to be so this is redundant in the case where the software
interpreting the messages understands the kind.The expected current state of the generation counter
(approximately the number of times this object has been
written, see below for details).The value or values to be stored. This may contain one or
more stored_data values depending on the data model associated
with each kind.The peer MUST perform the following checks:The kind_id is known and supported.The data_model matches the kind_id.The signatures over each individual data element (if any)
are valid.Each element is signed by a credential which is authorized
to write this kind at this Resource-IDFor original (non-replica) stores, the peer MUST check that
if the generation-counter is non-zero, it equals the current
value of the generation-counter for this kind. This feature
allows the generation counter to be used in a way similar to
the HTTP Etag feature.The storage time values are greater than that of any value
which would be replaced by this Store.If all these checks succeed, the peer MUST attempt to store the
data values. For non-replica stores, if the store succeeds and the
data is changed, then the peer must increase the generation
counter by at least one. If there are multiple stored values in a
single StoreKindData, it is permissible for the peer to increase
the generation counter by only 1 for the entire Kind-ID, or by 1
or more than one for each value. Accordingly, all stored data
values must have a generation counter of 1 or greater. 0 is used
in the Store request to indicate that the generation counter
should be ignored for processing this request, however the
responsible peer should increase the stored generation counter,
and should return the correct generation counter in the
response.For replica Stores, the peer MUST set the generation counter to
match the generation_counter in the message, and MUST NOT check
the generation counter against the current value. Replica Stores
MUST NOT use a generation counter of 0.When a peer stores data previously stored by another node
(e.g., for replicas or topology shifts) it MUST adjust the
lifetime value downward to reflect the amount of time the value
was stored at the peer.The properties of stores for each data model are as follows:
A store of a new single-value element creates the element
if it does not exist and overwrites any existing value with
the new value.A store of an array entry replaces (or inserts) the given
value at the location specified by the index. Because arrays
are sparse, a store past the end of the array extends it with
nonexistent values (exists=False) as required. A store at
index 0xffffffff places the new value at the end of the array
regardless of the length of the array. The resulting
StoredData has the correct index value when it is subsequently
fetched.A store of a dictionary entry replaces (or inserts) the
given value at the location specified by the dictionary
key.The following figure shows the relationship between these
structures for an example store which stores the following values
at resource "1234"The value "abc" in the single value slot for kind XThe value "foo" at index 0 in the array for kind YThe value "bar" at index 1 in the array for kind YIn response to a successful Store request the peer MUST return
a StoreAns message containing a series of StoreKindResponse
elements containing the current value of the generation counter
for each Kind-ID, as well as a list of the peers where the data
was/will-be replicated.;
} StoreKindResponse;
struct {
StoreKindResponse kind_responses<0..2^16-1>;
} StoreAns;
]]>The contents of each StoreKindResponse are:The Kind-ID being represented.The current value of the generation counter for that
Kind-ID.The list of other peers at which the data was/will-be
replicated. In overlays and applications where the responsible
peer is intended to store redundant copies, this allows the
storing peer to independently verify that the replicas were in
fact stored by doing its own Fetch.The response itself is just StoreKindResponse values packed
end-to-end.If any of the generation counters in the request precede the
corresponding stored generation counter, then the peer MUST fail
the entire request and respond with a Error_Data_Too_Old error.
The error_info in the ErrorResponse MUST be a StoreAns response
containing the correct generation counter for each kind and empty
replicas lists.If the data being stored is too large for the allowed limit by
the given usage, then the peer MUST fail the request and generate
an Error_Data_Too_Large error.This version of RELOAD (unlike previous versions) does not have
an explicit Remove operation. Rather, values are Removed by
storing "nonexistent" values in their place. Each DataValue
contains a boolean value called "exists" which indicates whether a
value is present at that location. In order to effectively remove
a value, the owner stores a new DataValue with:exists = falsevalue = {} (0 length)Storing nodes MUST treat these nonexistent values the same way
they treat any other stored value, including overwriting the
existing value, replicating them, and aging them out as necessary
when lifetime expires. When a stored nonexistent value's lifetime
expires, it is simply removed from the storing node like any other
stored value expiration. Note that in the case of arrays and
dictionaries, this may create an implicit, unsigned "nonexistent"
value to represent a gap in the data structure. However, this
value isn't persistent nor is it replicated, it's simply
synthesized by the storing node.The Fetch request retrieves one or more data elements stored at a
given Resource-ID. A single Fetch request can retrieve multiple
different kinds.;
case dictionary:
DictionaryKey keys<0..2^16-1>;
/* This structure may be extended */
} model_specifier;
} StoredDataSpecifier;
struct {
ResourceId resource;
StoredDataSpecifier specifiers<0..2^16-1>;
} FetchReq;
]]>The contents of the Fetch requests are as follows:The resource ID to fetch from.A sequence of StoredDataSpecifier values, each specifying
some of the data values to retrieve.Each StoredDataSpecifier specifies a single kind of data to
retrieve and (if appropriate) the subset of values that are to be
retrieved. The contents of the StoredDataSpecifier structure are
as follows:The Kind-ID of the data being fetched. Implementations
SHOULD reject requests corresponding to unknown kinds unless
specifically configured otherwise.The data model of the data. This must be checked against
the Kind-ID.The last generation counter that the requesting peer saw.
This may be used to avoid unnecessary fetches or it may be set
to zero.The length of the rest of the structure, thus allowing
extensibility.A reference to the data value being requested within the
data model specified for the kind. For instance, if the data
model is "array", it might specify some subset of the
values.The model_specifier is as follows:If the data is of data model single value, the specifier is
empty.If the data is of data model array, the specifier contains
of a list of ArrayRange elements, each of which contains two
integers. The first integer is the beginning of the range and
the second is the end of the range. 0 is used to indicate the
first element and 0xffffffff is used to indicate the final
element. The beginning of the range MUST be earlier in the
array then the end. The ranges MUST be non-overlapping.If the data is of data model dictionary then the specifier
contains a list of the dictionary keys being requested. If no
keys are specified, than this is a wildcard fetch and all
key-value pairs are returned. The generation-counter is used to indicate the requester's
expected state of the storing peer. If the generation-counter in
the request matches the stored counter, then the storing peer
returns a response with no StoredData values.Note that because the certificate for a user is typically
stored at the same location as any data stored for that user, a
requesting peer which does not already have the user's certificate
should request the certificate in the Fetch as an
optimization.The response to a successful Fetch request is a FetchAns
message containing the data requested by the requester.;
} FetchKindResponse;
struct {
FetchKindResponse kind_responses<0..2^32-1>;
} FetchAns;
]]>The FetchAns structure contains a series of FetchKindResponse
structures. There MUST be one FetchKindResponse element for each
Kind-ID in the request.The contents of the FetchKindResponse structure are as follows:
the kind that this structure is for.the generation counter for this kind.the relevant values. If the generation counter in the
request matches the generation-counter in the stored data,
then no StoredData values are returned. Otherwise, all
relevant data values MUST be returned. A nonexistent value is
represented with "exists" set to False.There is one subtle point about signature computation on
arrays. If the storing node uses the append feature (where the
index=0xffffffff), then the index in the StoredData that is
returned will not match that used by the storing node, which would
break the signature. In order to avoid this issue, the index value
in array is set to zero before the signature is computed. This
implies that malicious storing nodes can reorder array entries
without being detected. [[OPEN ISSUE: We've considered a number of
alternate designs here that would preserve security against this
attack if the storing node did not use the append feature.
However, they are more complicated for one or both sides. If this
attack is considered serious, we can introduce one of them.]]The Stat request is used to get metadata (length, generation
counter, digest, etc.) for a stored element without retrieving the
element itself. The name is from the UNIX stat(2) system call which
performs a similar function for files in a filesystem. It also
allows the requesting node to get a list of matching elements
without requesting the entire element.The Stat request is identical to the Fetch request. It simply
specifies the elements to get metadata about.;
} StatReq;
]]>The Stat response contains the same sort of entries that a
Fetch response would contain, however instead of containing the
element data it contains metadata.;
} MetaData;
struct {
uint32 index;
MetaData value;
} ArrayEntryMeta;
struct {
DictionaryKey key;
MetaData value;
} DictionaryEntryMeta;
struct {
DataModel model;
select (model) {
case single_value:
MetaData single_value_entry;
case array:
ArrayEntryMeta array_entry;
case dictionary:
DictionaryEntryMeta dictionary_entry;
/* This structure may be extended */
} ;
} MetaDataValue;
struct {
uint32 length;
uint64 storage_time;
uint32 lifetime;
MetaDataValue metadata;
} StoredMetaData;
struct {
KindId kind;
uint64 generation;
StoredMetaData values<0..2^32-1>;
} StatKindResponse;
struct {
StatKindResponse kind_responses<0..2^32-1>;
} StatAns;
]]>The structures used in StatAns parallel those used in FetchAns:
a response consists of multiple StatKindResponse values, one for
each kind that was in the request. The contents of the
StatKindResponse are the same as those in the FetchKindResponse,
except that the values list contains StoredMetaData entries
instead of StoredData entries.The contents of the StoredMetaData structure are the same as
the corresponding fields in StoredData except that there is no
signature field and the value is a MetaDataValue rather than a
StoredDataValue.A MetaDataValue is a variant structure, like a StoredDataValue,
except for the types of each arm, which replace DataValue with
MetaData.The only really new structure is MetaData, which has the
following contents: Same as in DataValueThe length of the stored value.The hash algorithm used to perform the digest of the
value.A digest of the value using hash_algorithm.The Find request can be used to explore the Overlay Instance. A
Find request for a Resource-ID R and a Kind-ID T retrieves the
Resource-ID (if any) of the resource of kind T known to the target
peer which is closes to R. This method can be used to walk the
Overlay Instance by interactively fetching R_n+1=nearest(1 +
R_n).
-->
The FindReq message contains a series of Resource-IDs and
Kind-IDs identifying the resource the peer is interested in.;
} FindReq;
]]>The request contains a list of Kind-IDs which the Find is for,
as indicated below: The desired Resource-IDThe desired Kind-IDs. Each value MUST only appear once.A response to a successful Find request is a FindAns message
containing the closest Resource-ID for each kind specified in the
request.;
} FindAns;
]]>If the processing peer is not responsible for the specified
Resource-ID, it SHOULD return a 404 error.For each Kind-ID in the request the response MUST contain a
FindKindData indicating the closest Resource-ID for that Kind-ID
unless the kind is not allowed to be used with Find in which case
a FindKindData for that Kind-ID MUST NOT be included in the
response. If a Kind-ID is not known, then the corresponding
Resource-ID MUST be 0. Note that different Kind-IDs may have
different closest Resource-IDs.The response is simply a series of FindKindData elements, one
per kind, concatenated end-to-end. The contents of each element
are:The Kind-ID.The closest resource ID to the specified resource ID. This
is 0 if no resource ID is known.Note that the response does not contain the contents of the
data stored at these Resource-IDs. If the requester wants this, it
must retrieve it using Fetch.There are two ways to define a new kind. The first is by writing
a document and registering the kind-id with IANA. This is the
preferred method for kinds which may be widely used and reused. The
second method is to simply define the kind and its parameters in the
configuration document using the section of kind-id space set aside
for private use. This method MAY be used to define ad hoc kinds in
new overlays.However a kind is defined, the definition must include:The meaning of the data to be stored (in some textual
form).The Kind-ID.The data model (single value, array, dictionary, etc.)The access control model.In addition, when kinds are registered with IANA, each kind is
assigned a short string name which is used to refer to it in
configuration documents.While each kind MUST define what data model is used for its data,
that does not mean that it must define new data models. Where
practical, kinds SHOULD use the built-in data models. However, they
MAY define any new required data models. The intention is that the
basic data model set be sufficient for most applications/usages.The Certificate Store usage allows a peer to store its certificate in
the overlay, thus avoiding the need to send a certificate in each
message - a reference may be sent instead.A user/peer MUST store its certificate at Resource-IDs derived from
two Resource Names:The user name in the certificate.The Node-ID in the certificate.Note that in the second case the certificate is not stored at the
peer's Node-ID but rather at a hash of the peer's Node-ID. The intention
here (as is common throughout RELOAD) is to avoid making a peer
responsible for its own data.A peer MUST ensure that the user's certificates are stored in the
Overlay Instance. New certificates are stored at the end of the list.
This structure allows users to store and old and new certificate the
both have the same Node-ID which allows for migration of certificates
when they are renewed.This usage defines the following kind:CERTIFICATEThe data model for CERTIFICATE data is
array.NODE-MATCH.The TURN server usage allows a RELOAD peer to advertise that it is
prepared to be a TURN server as defined in . When a node starts up, it joins
the overlay network and forms several connection in the process. If the
ICE stage in any of these connection return a reflexive address that is
not the same as the peers perceived address, then the peers is behind a
NAT and not an candidate for a TURN server. Additionally, if the peers
IP address is in the private address space range, then it is not a
candidate for a TURN server. Otherwise, the peer SHOULD assume it is a
potential TURN server and follow the procedures below.If the node is a candidate for a TURN server it will insert some
pointers in the overlay so that other peers can find it. The overlay
configuration file specifies a turnDensity parameter that indicates how
many times each TURN server should record itself in the overlay.
Typically this should be set to the reciprocal of the estimate of what
percentage of peers will act as TURN servers. For each value, called d,
between 1 and turnDensity, the peer forms a Resource Name by
concatenating its Peer-ID and the value d. This Resource Name is hashed
to form a Resource-ID. The address of the peer is stored at that
Resource-ID using type TURN-SERVICE and the TurnServer object:The contents of this structure are as follows: the d valuethe address at which the TURN server can be contacted.Correct functioning of this algorithm depends
critically on having turnDensity be an accurate estimate of the true
density of TURN servers. If turnDensity is too high, then the
process of finding TURN servers becomes extremely expensive as
multiple candidate Resource-IDs must be probed.Peers peers that provide this service need to support the TURN
extensions to STUN for media relay of both UDP and TCP traffic as
defined in and .[[OPEN ISSUE: This structure only works for TURN servers that have
public addresses. It may be possible to use TURN servers that are behind
well-behaved NATs by first ICE connecting to them. If we decide we want
to enable that, this structure will need to change to either be a
Peer-ID or include that as an option.]]This usage defines the following kind to indicate that the a peer is
willing to act as a TURN server:TURN-SERVICEThe TURN-SERVICE kind stores a single value
for each Resource-ID.NODE-MULTIPLE, with maximum iteration
counter 20.Peers can find other servers by selecting a random Resource-ID and
then doing a Find request for the appropriate server type with that
Resource-ID. The Find request gets routed to a random peer based on the
Resource-ID. If that peer knows of any servers, they will be returned.
The returned response may be empty if the peer does not know of any
servers, in which case the process gets repeated with some other random
Resource-ID. As long as the ratio of servers relative to peers is not
too low, this approach will result in finding a server relatively
quickly.This algorithm is assigned the name chord-128-2-16+ to indicate it is
based on Chord, uses SHA-1 then truncates that to 128 bit for the hash
function, stores 2 redundant copies of all data, and has finger tables
with at least 16 entries.The algorithm described here is a modified version of the Chord
algorithm. Each peer keeps track of a finger table of 16 entries and a
neighbor table of 6 entries. The neighbor table contains the 3 peers
before this peer and the 3 peers after it in the DHT ring. The first
entry in the finger table contains the peer half-way around the ring
from this peer; the second entry contains the peer that is 1/4 of the
way around; the third entry contains the peer that is 1/8th of the way
around, and so on. Fundamentally, the chord data structure can be
thought of a doubly-linked list formed by knowing the successors and
predecessor peers in the neighbor table, sorted by the Node-ID. As
long as the successor peers are correct, the DHT will return the
correct result. The pointers to the prior peers are kept to enable
inserting of new peers into the list structure. Keeping multiple
predecessor and successor pointers makes it possible to maintain the
integrity of the data structure even when consecutive peers
simultaneously fail. The finger table forms a skip list, so that
entries in the linked list can be found in O(log(N)) time instead of
the typical O(N) time that a linked list would provide.A peer, n, is responsible for a particular Resource-ID k if k is
less than or equal to n and k is greater than p, where p is the peer
id of the previous peer in the neighbor table. Care must be taken when
computing to note that all math is modulo 2^128.Open Issue: The algorithm currently presented in this section uses
reactive recovery when a neighbor is lost, that information is
immediately propagated. Research in DHT performance by Rhea et al.
indicates that this is not optimal in large-scale networks with churn
. Addressing this issue,
however, needs to take into account the requirements placed on this
algorithm. Because it is the mandatory DHT for RELOAD, the algorithm
described here is designed to meet two primary challenges: Scale from small (ten or fewer) overlays on a LAN to global
overlays with millions of nodesSimple to implementOne of the challenges these requirements entail is achieving
reasonable performance as the overlay scales without undue complexity.
We have two possibly conflicting concerns: A small-scale overlay may not be stable without reactive
recovery, because a single peer represents a large portion of the
overlay.A large-scale overlay with significant churn may perform
poorly, both in terms of traffic volume and success rates, when
using reactive recovery. As a result, multiple solutions have been proposed: Identify one set of behaviors that achieves adequate
functionality as the overlay scales.Add a parameter dictating the type of recovery used by peers in
the overlay, configuring the peers appropriately as they join the
overlay.Make the algorithm adaptive, according to the size of the
overlay or the churn rates observed.At IETF 72, the WG elected to defer a decision on the final choice
until data could be collected on the effectiveness of the strategies.
This section, therefore, retains the reactive recovery model until
evidence supporting a decision is available.If a peer is not responsible for a Resource-ID k, but is directly
connected to a node with Node-ID k, then it routes the message to that
node. Otherwise, it routes the request to the peer in the routing
table that has the largest Node-ID that is in the interval between the
peer and k. The routing table is the union of the neighbor table and
the finger table.When a peer receives a Store request for Resource-ID k, and it is
responsible for Resource-ID k, it stores the data and returns a
success response. [[Open Issue: should it delay sending this success
until it has successfully stored the redundant copies?]]. It then
sends a Store request to its successor in the neighbor table and to
that peers successor. Note that these Store requests are addressed to
those specific peers, even though the Resource-ID they are being asked
to store is outside the range that they are responsible for. The peers
receiving these check they came from an appropriate predecessor in
their neighbor table and that they are in a range that this
predecessor is responsible for, and then they store the data. They do
not themselves perform further Stores because they can determine that
they are not responsible for the Resource-ID.Note that a malicious node can return a success response but not
store the data locally or in the replica set. Requesting peers that
wish to ensure that the replication actually occurred SHOULD [[Open
Issue: SHOULD or MAY?]] contact each peer listed in the replicas field
of the Store response and retrieve a copy of the data. The join process for a joining party (JP) with Node-ID n is as
follows.JP connects to its chosen bootstrap node.JP uses a series of Probes to populate its routing table.JP sends Attach requests to initiate connections to each of the
peers in the connection table as well as to the desired finger
table entries. Note that this does not populate their routing
tables, but only their connection tables, so JP will not get
messages that it is expected to route to other nodes.JP enters all the peers it contacted into its routing
table.JP sends a Join to its immediate successor, the admitting peer
(AP) for Node-ID n. The AP sends the response to the Join.AP does a series of Store requests to JP to store the data that
JP will be responsible for.AP sends JP an Update explicitly labeling JP as its
predecessor. At this point, JP is part of the ring and responsible
for a section of the overlay. AP can now forget any data which is
assigned to JP and not AP.AP sends an Update to all of its neighbors with the new values
of its neighbor set (including JP).JP sends Updates to all the peers in its routing table.In order to populate its routing table, JP sends a Probe via the
bootstrap node directed at Resource-ID n+1 (directly after its own
Resource-ID). This allows it to discover its own successor. Call that
node p0. It then sends a probe to p0+1 to discover its successor (p1).
This process can be repeated to discover as many successors as
desired. The values for the two peers before p will be found at a
later stage when n receives an Update.In order to set up its neighbor table entry for peer i, JP simply
sends an Attach to peer (n+2^(numBitsInNodeId-i). This will be routed
to a peer in approximately the right location around the ring.When a peer needs to Attach to a new peer in its neighbor table, it
MUST source-route the Attach request through the peer from which it
learned the new peer's Node-ID. Source-routing these requests allows
the overlay to recover from instability.All other Attach requests, such as those for new finger table
entries, are routed conventionally through the overlay.If a peer is unable to successfully Attach with a peer that should
be in its neighborhood, it MUST locate either a TURN server or another
peer in the overlay, but not in its neighborhood, through which it can
exchange messages with its neighbor peerA chord Update is defined as;
NodeId successors<0..2^16-1>;
case full:
NodeId predecessors<0..2^16-1>;
NodeId successors<0..2^16-1>;
NodeId fingers<0..2^16-1>;
};
} ChordUpdate;
]]>The "type" field contains the type of the update, which depends on
the reason the update was sent.this peer is ready to receive messages.
This message is used to indicate that a node which has Attached is
a peer and can be routed through. It is also used as a
connectivity check to non-neighbor peers.this version is sent to members of the
Chord neighbor table.this version is sent to peers which request
an Update with a RouteQueryReq.If the message is of type "neighbors", then the contents of the
message will be:The predecessor set of the Updating peer.The successor set of the Updating peer.If the message is of type "full", then the contents of the message
will be:The predecessor set of the Updating peer.The successor set of the Updating peer.The finger table if the Updating peer, in numerically ascending
order.A peer MUST maintain an association (via Attach) to every member of
its neighbor set. A peer MUST attempt to maintain at least three
predecessors and three successors. However, it MUST send its entire
set in any Update message sent to neighbors.Every time a connection to a peer in the neighbor table is lost
(as determined by connectivity probes or failure of some request),
the peer should remove the entry from its neighbor table and replace
it with the best match it has from the other peers in its routing
table. It then sends an Update to all its remaining neighbors. The
update will contain all the Node-IDs of the current entries of the
table (after the failed one has been removed). Note that when
replacing a successor the peer SHOULD delay the creation of new
replicas for 30 seconds after removing the failed entry from its
neighbor table in order to allow a triggered update to inform it of
a better match for its neighbor table.If connectivity is lost to all three of the peers that follow
this peer in the ring, then this peer should behave as if it is
joining the network and use Probes to find a peer and send it a
Join. If connectivity is lost to all the peers in the finger table,
this peer should assume that it has been disconnected from the rest
of the network, and it should periodically try to join the DHT.When a peer, N, receives an Update request, it examines the
Node-IDs in the UpdateReq and at its neighbor table and decides if
this UpdateReq would change its neighbor table. This is done by
taking the set of peers currently in the neighbor table and
comparing them to the peers in the update request. There are three
major cases:The UpdateReq contains peers that would not change the
neighbor set because they match the neighbor table.The UpdateReq contains peers closer to N than those in its
neighbor table.The UpdateReq defines peers that indicate a neighbor table
further away from N than some of its neighbor table. Note that
merely receiving peers further away does not demonstrate this,
since the update could be from a node far away from N. Rather,
the peers would need to bracket N.In the first case, no change is needed.In the second case, N MUST attempt to Attach to the new peers and
if it is successful it MUST adjust its neighbor set accordingly.
Note that it can maintain the now inferior peers as neighbors, but
it MUST remember the closer ones.The third case implies that a neighbor has disappeared, most
likely because it has simply been disconnected but perhaps because
of overlay instability. N MUST Probe the questionable peers to
discover if they are indeed missing and if so, remove them from its
neighbor table.After any Probes and Attaches are done, if the neighbor table
changes, the peer sends an Update request to each of its neighbors
that was in either the old table or the new table. These Update
requests are what ends up filling in the predecessor/successor
tables of peers that this peer is a neighbor to. A peer MUST NOT
enter itself in its successor or predecessor table and instead
should leave the entries empty.If peer N which is responsible for a Resource-ID R discovers that
the replica set for R (the next two nodes in its successor set) has
changed, it MUST send a Store for any data associated with R to any
new node in the replica set. It SHOULD NOT delete data from peers
which have left the replica set.When a peer N detects that it is no longer in the replica set for
a resource R (i.e., there are three predecessors between N and R),
it SHOULD delete all data associated with R from its local
store.There are four components to stabilization: exchange Updates with all peers in its routing table to
exchange statesearch for better peers to place in its finger tablesearch to determine if the current finger table size is
sufficiently largesearch to determine if the overlay has partitioned and needs
to recoverA peer MUST periodically send an Update request to every peer in
its routing table. The purpose of this is to keep the predecessor
and successor lists up to date and to detect connection failures.
The default time is about every ten minutes, but the enrollment
server SHOULD set this in the configuration document using the
"chord-128-2-16+-update-frequency" element (denominated in seconds.)
A peer SHOULD randomly offset these Update requests so they do not
occur all at once. If an Update request fails or times out, the peer
MUST mark that entry in the neighbor table invalid and attempt to
reestablish a connection. If no connection can be established, the
peer MUST attempt to establish a new peer as its neighbor and do
whatever replica set adjustments are required. If a finger table
entry is found to have failed, the peer MUST search for a
replacement as directed below.A peer MUST periodically select a random entry i from the finger
table and evaluate whether that entry should be replaced. The
default time interval is about every hour, but the enrollment server
SHOULD set this in the configuration document using the
"chord-128-2-16+-probe-frequency" element (denominated in
seconds).To evaluate whether the i'th finger table entry needs to be
replaced, if the Node-ID of the entry is not valid for that finger
table entry, the peer SHOULD search for a better entry. A peer
searches for a better entry using a Probe request. If the Probe
returns a different peer than the one currently in this entry of the
finger table, then a new connection should be formed to replace the
old entry in the finger table.A peer SHOULD consider the finger table entry valid if it is in
the range [n+2^(numBitsInNodeId-i),
n+2^(numBitsInNodeId-(i-1))-2^(numBitsInNodeId-(i+1))]. When
searching for a better entry, the peer SHOULD send the Probe to a
Node-ID selected randomly from that range. Random selection is
preferred over a search for strictly spaced entries to minimize the
effect of churn on overlay routing . An implementation or
subsequent specification MAY choose a method for selecting finger
table entries other than choosing randomly within the range. It is
RECOMMENDED that any such alternate methods be employed only on
finger table stabilization and not for the selection of initial
finger table entries unless the alternative method is faster and
imposes less overhead on the overlay.As an overlay grows, more than 16 entries may be required in the
finger table for efficient routing. To determine if its finger table
is sufficiently large, once an hour the peer should perform a Probe
to determine whether growing its finger table by four entries would
result in it learning at least two peers that it does not already
have in its neighbor table. If so, then the finger table SHOULD be
grown by four entries. Similarly, if the peer observes that its
closest finger table entries are also in its neighbor table, it MAY
shrink its finger table to the minimum size of 16 entries. [[OPEN
ISSUE: there are a variety of algorithms to gauge the population of
the overlay and select an appropriate finger table size. Need to
consider which is the best combination of effectiveness and
simplicity. Also, an example would help here.]]To detect that a partitioning has occurred and to heal the
overlay, a peer P MUST periodically repeat the discovery process
used in the initial join for the overlay to locate an appropriate
bootstrap peer, B. If an overlay has multiple mechanisms for
discovery it should randomly select a method to locate a bootstrap
peer. P should then send a Probe for its own Node-ID routed through
B. If a response is received from a peer S', which is not P's
successor, then the overlay is partitioned and P should send a
Attach to S' routed through B, followed by an Update sent to S'.
(Note that S' may not be in P's neighbor table once the overlay is
healed, but the connection will allow S' to discover appropriate
neighbor entries for itself via its own stabilization.)For this topology plugin, the RouteQueryReq contains no additional
information. The RouteQueryAns contains the single node ID of the next
peer to which the responding peer would have routed the request
message in recursive routing:The contents of this structure are as follows: The peer to which the responding peer would route the message
to in order to deliver it to the destination listed in the
request.If the requester set the send_update flag, the responder SHOULD
initiate an Update immediately after sending the RouteQueryAns.Peers SHOULD send a Leave request prior to exiting the Overlay
Instance. Any peer which receives a Leave for a peer n in its neighbor
set must remove it from the neighbor set, update its replica sets as
appropriate (including Stores of data to new members of the replica
set) and send Updates containing its new predecessor and successor
tables.This specification defines a new content type
"application/p2p-overlay+xml" for an MIME entity that contains overlay
information. An example document is shown below.false192.0.0.1:5678192.0.2.2:6789 30 false4000https://example.org foo 192.0.0.3:5678300400falseasecretChord-128-2-16TODOsingleuser-match1100arrayuser-match2241TODO BASE 64 encoded security block
]]>The file MUST be a well formed XML document and it SHOULD contain
an encoding declaration in the XML declaration. If the charset
parameter of the MIME content type declaration is present and it is
different from the encoding declaration, the charset parameter takes
precedence. Every application conforming to this specification MUST
accept the UTF-8 character encoding to ensure minimal
interoperability. The namespace for the elements defined in this
specification is urn:ietf:params:xml:ns:p2p:config-base and
urn:ietf:params:xml:ns:p2p:config-chord-128-2".The file can contain multiple "configuration" elements where each
one contains the configuration information for a different overlay.
Each "configuration" has the following attributes:name of the overlaytime in future at which this overlay
configuration is not longer valid and need to be retrieved
againa monotonically increasing sequence number
between 1 and 65534Inside each overlay element, the following elements can occur:This element has an attribute called
algorithm-name that describes the overlay-algorithm being
used.This element contains a PEM encoded
X.509v3 certificate that is the root trust store used to sign all
certificates in this overlay. There can be more than one of
these.This element indicates the kinds
that members must support. It has three attributes: kind: either a string representing the kind (the name
registered to IANA) or an integer kind-id allocated out of
private spacemax-count: the maximum number of values which members of
the overlay must support.data-model: the data model to be used.max-size: the maximum size of individual values.access-control: the access control model to be used. All of these values MUST be provided. If the kind is
registered with IANA, the data-model and access-control attributes
MUST match those in the kind registration. For instance, the
example above indicates that members must support SIP-REGISTRATION
with a maximum of 10 values of up to 1000 bytes each. Multiple
required-kinds elements MAY be present. [TODO: we need some way to
indicate iteration counters for NODE-MULTIPLE. Can some XML wizard
help?]This element contains the URL at
which the credential server can be reached in a "url" element.
This URL MUST be of type "https:". More than one credential-server
element may be present.This element indicates
whether self-signed certificates are permitted. If it is set to
"true", then self-signed certificates are allowed, in which case
the credential-server and root-cert elements may be absent.
Otherwise, it SHOULD be absent, but MAY be set "false". This
element also contains an attribute "digest" which indicates the
digest to be used to compute the Node-ID. Valid values for this
parameter are "SHA-1" and "SHA-256".This elements represents the address
of one of the bootstrap peers. It has an attribute called
"address" that represents the IP address (either IPv4 or IPv6,
since they can be distinguished) and an attribute called "port"
that represents the port. More than one bootstrap-peer element may
be present.This element represents the
address of a multicast address and port that may be used for
bootstrap and that peers SHOULD listen on to enable bootstrap. It
has an attributed called "address" that represents the IP address
and an attribute called "port" that represents the port. More than
one "multicast-bootstrap" element may be present.This element represents whether
clients are permitted or whether all nodes must be peers. If it is
set to "TRUE" or absent, this indicates that clients are
permitted. If it is set to "FALSE" then nodes MUST join as
peers.This element represents
whether nodes are allowed to use the AttachLite request in this
overlay. If it is absent, it is treated as if it was set to
"FALSE".The update
frequency for the Chord-128-2-16+ topology plugin (see ).The probe frequency
for the Chord-128-2-16+ topology plugin (see ).Base URL for credential
server.If shared secret mode is used, this
contains the shared secret.Maximum size in bytes of any
message in the overlay. If this value is not present, the default
is 5000.Initial default TTL (time to live, see
section XXX) for messages. If this value is not present, the
default is 100.The configuration file is a binary file and can not be changed,
<<<<<<< .mine
including whitepsace changes or the signature will break. The signature
is computed by taking each configuration element and starting from, and
including, the first < at the start of <configuration> up to
and including the > in </configuration> and treating this as a
binary blob thats sigend using the standard SecurityBlock defined in
TODO REF SECTION. The SecurityBlock
is base-64 encoded using the base-64 alphabet from and put in the signature element following the
configuration object in the config file.
=======
including whitepsace changes or the signature will break. The
signature is computed by taking each configuration element and
starting form, and including, the first < at the start of
<configuration> up to and including the > in
</configuration> and treating this as a binary blob thats sigend
using the standard SecurityBlock defined in . The SecurityBlock is
base 64 encoded using base64 alphabet from RFC and put in the signature element following
the configuration object in the config file.
>>>>>>> .r3427
The grammar for the configuration data is:When a peer first joins a new overlay, it starts with a discovery
process to find an enrollment server. Related work to the approach
used here is described in and . Another
scheme for referencing overlays is described in . The peer first
determines the overlay name. This value is provided by the user or
some other out of band provisioning mechanism. If the name is an IP
address, that is directly used otherwise the peer MUST do a DNS SRV
query using a Service name of "p2p_enroll" and a protocol of tcp to
find an enrollment server.Once an address for the enrollment servers is determined, the peer
forms an HTTPS connection to that IP address. The certificate MUST
match the overlay name as described in .Whenever a peer contacts the enrollment server, it MUST fetch a new
copy of the configuration file. To do this, the peer performs a GET to
the URL formed by appending a path of "/p2psip/enroll" to the overlay
name. For example, if the overlay name was example.com, the URL would
be "https://example.com/p2psip/enroll". The result is an XML
configuration file described above, which replaces any previously
learned configuration file for this overlay.[[OPEN ISSUE: for unsecured overlays or overlays not specified by
domain name, need to specify another way to obtain/validate certs and
to update configuration info]]If the configuration document contains a credential-server element,
credentials are required to join the Overlay Instance. A peer which
does not yet have credentials MUST contact the credential server to
acquire them.RELOAD defines its own trivial certificate request protocol. We
would have liked to use an existing protocol, but were concerned about
the implementation burden of even the simplest of those protocols,
such as ) and . Our objective was to have a protocol which
could be easily implemented in a Web server which the operator did not
control (e.g., in a hosted service) and was compatible with the
existing certificate handling tooling as used with the Web certificate
infrastructure. This means accepting bare PKCS#10 requests and
returning a single bare X.509 certificate. Although the MIME types for
these objects are defined, none of the existing protocols support
exactly this model.The certificate request protocol is performed over HTTPS. The
request is an HTTP POST with the following properties:If authentication is required, there is a URL parameter of
"password" containing the user's password in the clear (hence the
need for HTTPS)The body is of content type "application/pkcs10", as defined in
.The Accept header contains the type "application/pkix-cert",
indicating the type that is expected in the response.The credential server MUST authenticate the request using the
provided user name and password. If the authentication succeeds and
the requested user name is acceptable, the server and returns a
certificate. The SubjectAltName field in the certificate contains the
following values:One or more Node-IDs which MUST be cryptographically random
. These MUST be chosen by the
credential server in such a way that they are unpredictable to the
requesting user. These are of type URI and MUST contain RELOAD
URIs as described in and
MUST contain a Destination list with a single entry of type
"node_id".The names this user is allowed to use in the overlay, using
type rfc822Name.The certificate is returned as type "application/pkix-cert", with
an HTTP status code of 200 OK. Certificate processing errors should be
treated as HTTP errors and have appropriate HTTP stats codes. [TODO:
There needs to be some text here about how the interaction with other
HTTP features works. This awaits the example from the apps ADs with
HELD.]The client MUST check that the certificate returned was signed by
one of the certificates received in the "root-cert" list of the
overlay configuration data. The peer then reads the certificate to
find the Node-IDs it can use.If the "self-signed-permitted" element is present and set to
"TRUE", then a node MUST generate its own self-signed certificate to
join the overlay. The self-signed certificate MAY contain any user
name of the users choice. Users SHOULD make some attempt to make it
unique but this document does not specify any mechanisms for
that.The Node-ID MUST be computed by applying the digest specified in
the self-signed-permitted element to the DER representation of the
user's public key. When accepting a self-signed certificate, nodes
MUST check that the Node-ID and public keys match. This prevents
Node-ID theft.Once the node has constructed a self-signed certificate, it MAY
join the overlay. Before storing its certificate in the overlay
() it SHOULD look to see if
the user name is already taken and if so choose another user name.
Note that this only provides protection against accidental name
collisions. Name theft is still possible. If protection against name
theft is desired, then the enrollment service must be used.In order to join the overlay, the peer MUST contact a peer.
Typically this means contacting the bootstrap peers, since they are
guaranteed to have public IP addresses (the system should not
advertise them as bootstrap peers otherwise). If the peer has cached
peers it SHOULD contact them first by sending a Probe request to the
known peer address with the destination Node-ID set to that peer's
Node-ID.If no cached peers are available, then the peer SHOULD send a Probe
request to the address and port found in the broadcast-peers element
in the configuration document. This MAY be a multicast or anycast
address. The Probe should use the wildcard Node-ID as the destination
Node-ID.The responder peer that receives the Probe request SHOULD check
that the overlay name is correct and that the requester peer sending
the request has appropriate credentials for the overlay before
responding to the Probe request even if the response is only an
error.When the requester peer finally does receive a response from some
responding peer, it can note the Node-ID in the response and use this
Node-ID to start sending requests to join the Overlay Instance as
described in .After a peer has successfully joined the overlay network, it SHOULD
periodically look at any peers to which it has managed to form direct
connections. Some of these peers MAY be added to the cached-peers list
and used in future boots. Peers that are not directly connected MUST
NOT be cached. The RECOMMENDED number of peers to cache is 10.In the following example, we assume that JP has formed a connection
to one of the bootstrap peers. JP then sends an Attach through that peer
to the admitting peer (AP) to initiate a connection. When AP responds,
JP and AP use ICE to set up a connection and then set up TLS.|
| | | | | | |
| | | | | | |
| | |Attach Dest=JP | | |
| | |<--------------------------------------|
| | | | | | |
| | | | | | |
| | |Attach Dest=JP | | |
| | |-------->| | | |
| | | | | | |
| | | | | | |
| | |AttachAns | | |
| | |<--------| | | |
| | | | | | |
| | | | | | |
| | |AttachAns | | |
| | |-------------------------------------->|
| | | | | | |
| | | | | | |
|AttachAns | | | | |
|<----------------------------------------------------------|
| | | | | | |
| | | | | | |
|TLS | | | | | |
|.............................| | | |
| | | | | | |
| | | | | | |
| | | | | | |
| | | | | | |
]]>Once JP has connected to AP, it needs to populate its Routing Table.
In Chord, this means that it needs to populate its neighbor table and
its finger table. To populate its neighbor table, it needs the successor
of AP, NP. It sends an Attach to the Resource-IP AP+1, which gets routed
to NP. When NP responds, JP and NP use ICE and TLS to set up a
connection.[[TODO: there should be a Probe here before populating]]| | | |
| | | | | | |
| | | | | | |
| | | |Attach AP+1 | |
| | | |-------->| | |
| | | | | | |
| | | | | | |
| | | |AttachAns | |
| | | |<--------| | |
| | | | | | |
| | | | | | |
|AttachAns | | | | |
|<----------------------------| | | |
| | | | | | |
| | | | | | |
|Attach | | | | | |
|-------------------------------------->| | |
| | | | | | |
| | | | | | |
|TLS | | | | | |
|.......................................| | |
| | | | | | |
| | | | | | |
| | | | | | |
| | | | | | |
]]>JP also needs to populate its finger table (for Chord). It issues a
Attach to a variety of locations around the overlay. The diagram below
shows it sending an Attach halfway around the Chord ring the JP +
2^127.| | |
| | | |
| | | |
| |Attach JP+2<<126 |
| |-------->| |
| | | |
| | | |
| | |Attach JP+2<<126
| | |-------->|
| | | |
| | | |
| | |AttachAns|
| | |<--------|
| | | |
| | | |
| |AttachAns| |
| |<--------| |
| | | |
| | | |
|AttachAns| | |
|<--------| | |
| | | |
| | | |
|TLS | | |
|.............................|
| | | |
| | | |
| | | |
| | | |
]]>Once JP has a reasonable set of connections he is ready to take his
place in the DHT. He does this by sending a Join to AP. AP does a series
of Store requests to JP to store the data that JP will be responsible
for. AP then sends JP an Update explicitly labeling JP as its
predecessor. At this point, JP is part of the ring and responsible for a
section of the overlay. AP can now forget any data which is assigned to
JP and not AP.| | | |
| | | | | | |
| | | | | | |
|JoinAns | | | | | |
|<----------------------------| | | |
| | | | | | |
| | | | | | |
|StoreReq Data A | | | | |
|<----------------------------| | | |
| | | | | | |
| | | | | | |
|StoreAns | | | | | |
|---------------------------->| | | |
| | | | | | |
| | | | | | |
|StoreReq Data B | | | | |
|<----------------------------| | | |
| | | | | | |
| | | | | | |
|StoreAns | | | | | |
|---------------------------->| | | |
| | | | | | |
| | | | | | |
|UpdateReq| | | | | |
|<----------------------------| | | |
| | | | | | |
| | | | | | |
|UpdateAns| | | | | |
|---------------------------->| | | |
| | | | | | |
| | | | | | |
| | | | | | |
| | | | | | |
]]>In Chord, JP's neighbor table needs to contain its own predecessors.
It couldn't connect to them previously because Chord has no way to route
immediately to your predecessors. However, now that it has received an
Update from AP, it has APs predecessors, which are also its own, so it
sends Attaches to them. Below it is shown connecting to its closest
predecessor, PP.| | | |
| | | | | | |
| | | | | | |
| | |Attach Dest=PP | | |
| | |<--------| | | |
| | | | | | |
| | | | | | |
| | |AttachAns| | | |
| | |-------->| | | |
| | | | | | |
| | | | | | |
|AttachAns| | | | | |
|<----------------------------| | | |
| | | | | | |
| | | | | | |
|TLS | | | | | |
|...................| | | | |
| | | | | | |
| | | | | | |
|UpdateReq| | | | | |
|------------------>| | | | |
| | | | | | |
| | | | | | |
|UpdateAns| | | | | |
|<------------------| | | | |
| | | | | | |
| | | | | | |
|UpdateReq| | | | | |
|---------------------------->| | | |
| | | | | | |
| | | | | | |
|UpdateAns| | | | | |
|<----------------------------| | | |
| | | | | | |
| | | | | | |
|UpdateReq| | | | | |
|-------------------------------------->| | |
| | | | | | |
| | | | | | |
|UpdateAns| | | | | |
|<--------------------------------------| | |
| | | | | | |
| | | | | | |
]]>Finally, now that JP has a copy of all the data and is ready to route
messages and receive requests, it sends Updates to everyone in its
Routing Table to tell them it is ready to go. Below, it is shown sending
such an update to TP.|
| | | |
| | | |
|UpdateAns| | |
|<----------------------------|
| | | |
| | | |
| | | |
| | | |
]]>RELOAD provides a generic storage service, albeit one designed to
be useful for P2PSIP. In this section we discuss security issues that
are likely to be relevant to any usage of RELOAD.In any Overlay Instance, any given user depends on a number of
peers with which they have no well-defined relationship except that
they are fellow members of the Overlay Instance. In practice, these
other nodes may be friendly, lazy, curious, or outright malicious. No
security system can provide complete protection in an environment
where most nodes are malicious. The goal of security in RELOAD is to
provide strong security guarantees of some properties even in the face
of a large number of malicious nodes and to allow the overlay to
function correctly in the face of a modest number of malicious
nodes.P2PSIP deployments require the ability to authenticate both peers
and resources (users) without the active presence of a trusted entity
in the system. We describe two mechanisms. The first mechanism is
based on public key certificates and is suitable for general
deployments. The second is an admission control mechanism based on an
overlay-wide shared symmetric key.The two basic functions provided by overlay nodes are storage and
routing: some node is responsible for storing a peer's data and for
allowing a peer to fetch other peer's data. Some other set of nodes
are responsible for routing messages to and from the storing nodes.
Each of these issues is covered in the following sections.P2P overlays are subject to attacks by subversive nodes that may
attempt to disrupt routing, corrupt or remove user registrations, or
eavesdrop on signaling. The certificate-based security algorithms we
describe in this draft are intended to protect overlay routing and
user registration information in RELOAD messages.To protect the signaling from attackers pretending to be valid
peers (or peers other than themselves), the first requirement is to
ensure that all messages are received from authorized members of the
overlay. For this reason, RELOAD transports all messages over a secure
channel (TLS and DTLS are defined in this document) which provides
message integrity and authentication of the directly communicating
peer. In addition, messages and data are digitally signed with the
sender's private key, providing end-to-end security for
communications.This specification stores users' registrations and possibly other
data in an overlay network. This requires a solution to securing this
data as well as securing, as well as possible, the routing in the
overlay. Both types of security are based on requiring that every
entity in the system (whether user or peer) authenticate
cryptographically using an asymmetric key pair tied to a
certificate.When a user enrolls in the Overlay Instance, they request or are
assigned a unique name, such as "alice@dht.example.net". These names
are unique and are meant to be chosen and used by humans much like a
SIP Address of Record (AOR) or an email address. The user is also
assigned one or more Node-IDs by the central enrollment authority.
Both the name and the peer ID are placed in the certificate, along
with the user's public key.Each certificate enables an entity to act in two sorts of
roles:As a user, storing data at specific Resource-IDs in the Overlay
Instance corresponding to the user name.As a overlay peer with the peer ID(s) listed in the
certificate.Note that since only users of this Overlay Instance need to
validate a certificate, this usage does not require a global PKI.
Instead, certificates are signed by require a central enrollment
authority which acts as the certificate authority for the Overlay
Instance. This authority signs each peer's certificate. Because each
peer possesses the CA's certificate (which they receive on enrollment)
they can verify the certificates of the other entities in the overlay
without further communication. Because the certificates contain the
user/peer's public key, communications from the user/peer can be
verified in turn.If self-signed certificates are used, then the security provided is
significantly decreased, since attackers can mount Sybil attacks. In
addition, attackers cannot trust the user names in certificates
(though they can trust the Node-IDs because they are cryptographically
verifiable). This scheme is only appropriate for small deployments,
such as a small office or ad hoc overlay set up among participants in
a meeting. Some additional security can be provided by using the
shared secret admission control scheme as well.Because all stored data is signed by the owner of the data the
storing peer can verify that the storer is authorized to perform a
store at that Resource-ID and also allows any consumer of the data to
verify the provenance and integrity of the data when it retrieves
it.All implementations MUST implement certificate-based security.RELOAD also supports a shared secret admission control scheme that
relies on a single key that is shared among all members of the
overlay. It is appropriate for small groups that wish to form a
private network without complexity. In shared secret mode, all the
peers share a single symmetric key which is used to key TLS-PSK or TLS-SRP
mode. A peer which does not know the key cannot form TLS connections
with any other peer and therefore cannot join the overlay.One natural approach to a shared-secret scheme is to use a
user-entered password as the key. The difficulty with this is that in
TLS-PSK mode, such keys are very susceptible to dictionary attacks. If
passwords are used as the source of shared-keys, then TLS-SRP is a
superior choice because it is not subject to dictionary attacks.When certificate-based security is used in RELOAD, any given
Resource-ID/Kind-ID pair (a slot) is bound to some small set of
certificates. In order to write data in a slot, the writer must prove
possession of the private key for one of those certificates. Moreover,
all data is stored signed by the certificate which authorized its
storage. This set of rules makes questions of authorization and data
integrity - which have historically been thorny for overlays -
relatively simple.When a client wants to store some value in a slot, it first
digitally signs the value with its own private key. It then sends a
Store request that contains both the value and the signature towards
the storing peer (which is defined by the Resource Name construction
algorithm for that particular kind of value).When the storing peer receives the request, it must determine
whether the storing client is authorized to store in this slot. In
order to do so, it executes the Resource Name construction algorithm
for the specified kind based on the user's certificate information.
It then computes the Resource-ID from the Resource Name and verifies
that it matches the slot which the user is requesting to write to.
If it does, the user is authorized to write to this slot, pending
quota checks as described in the next section.For example, consider the certificate with the following
properties:If Alice wishes to Store a value of the "SIP Location" kind, the
Resource Name will be the SIP AOR "sip:alice@dht.example.com". The
Resource-ID will be determined by hashing the Resource Name. When a
peer receives a request to store a record at Resource-ID X, it takes
the signing certificate and recomputes the Resource Name, in this
case "alice@dht.example.com". If H("alice@dht.example.com")=X then
the Store is authorized. Otherwise it is not. Note that the Resource
Name construction algorithm may be different for other kinds.Being a peer in a Overlay Instance carries with it the
responsibility to store data for a given region of the Overlay
Instance. However, if clients were allowed to store unlimited
amounts of data, this would create unacceptable burdens on peers, as
well as enabling trivial denial of service attacks. RELOAD addresses
this issue by requiring configurations to define maximum sizes for
each kind of stored data. Attempts to store values exceeding this
size MUST be rejected (if peers are inconsistent about this, then
strange artifacts will happen when the zone of responsibility shifts
and a different peer becomes responsible for overlarge data).
Because each slot is bound to a small set of certificates, these
size restrictions also create a distributed quota mechanism, with
the quotas administered by the central enrollment server.Allowing different kinds of data to have different size
restrictions allows new usages the flexibility to define limits that
fit their needs without requiring all usages to have expansive
limits.Because each stored value is signed, it is trivial for any
retrieving peer to verify the integrity of the stored value. Some
more care needs to be taken to prevent version rollback attacks.
Rollback attacks on storage are prevented by the use of store times
and lifetime values in each store. A lifetime represents the latest
time at which the data is valid and thus limits (though does not
completely prevent) the ability of the storing node to perform a
rollback attack on retrievers. In order to prevent a rollback attack
at the time of the Store request, we require that storage times be
monotonically increasing. Storing peers MUST reject Store requests
with storage times smaller than or equal to those they are currently
storing. In addition, a fetching node which receives a data value
with a storage time older than the result of the previous fetch
knows a rollback has occurred.The mechanisms described here provide a high degree of security,
but some attacks remain possible. Most simply, it is possible for
storing nodes to refuse to store a value (i.e., reject any request).
In addition, a storing node can deny knowledge of values which it
previously accepted. To some extent these attacks can be ameliorated
by attempting to store to/retrieve from replicas, but a retrieving
client does not know whether it should try this or not, since there
is a cost to doing so.Although the certificate-based authentication scheme prevents a
single peer from being able to forge data owned by other peers.
Furthermore, although a subversive peer can refuse to return data
resources for which it is responsible it cannot return forged data
because it cannot provide authentication for such registrations.
Therefore parallel searches for redundant registrations can mitigate
most of the affects of a compromised peer. The ultimate reliability
of such an overlay is a statistical question based on the
replication factor and the percentage of compromised peers.In addition, when a kind is multivalued (e.g., an array data
model), the storing node can return only some subset of the values,
thus biasing its responses. This can be countered by using single
values rather than sets, but that makes coordination between
multiple storing agents much more difficult. This is a trade off
that must be made when designing any usage.Because the storage security system guarantees (within limits) the
integrity of the stored data, routing security focuses on stopping the
attacker from performing a DOS attack on the system by misrouting
requests in the overlay. There are a few obvious observations to make
about this. First, it is easy to ensure that an attacker is at least a
valid peer in the Overlay Instance. Second, this is a DOS attack only.
Third, if a large percentage of the peers on the Overlay Instance are
controlled by the attacker, it is probably impossible to perfectly
secure against this.In general, attacks on DHT routing are mounted by the attacker
arranging to route traffic through or two nodes it controls. In the
Eclipse attack the attacker tampers
with messages to and from nodes for which it is on-path with respect
to a given victim node. This allows it to pretend to be all the
nodes that are reachable through it. In the Sybil attack , the attacker registers a large number of
nodes and is therefore able to capture a large amount of the traffic
through the DHT.Both the Eclipse and Sybil attacks require the attacker to be
able to exercise control over her peer IDs. The Sybil attack
requires the creation of a large number of peers. The Eclipse attack
requires that the attacker be able to impersonate specific peers. In
both cases, these attacks are limited by the use of centralized,
certificate-based admission control.Admission to an RELOAD Overlay Instance is controlled by
requiring that each peer have a certificate containing its peer ID.
The requirement to have a certificate is enforced by using
certificate-based mutual authentication on each connection. Thus,
whenever a peer connects to another peer, each side automatically
checks that the other has a suitable certificate. These peer IDs are
randomly assigned by the central enrollment server. This has two
benefits:It allows the enrollment server to limit the number of peer
IDs issued to any individual user.It prevents the attacker from choosing specific peer IDs.The first property allows protection against Sybil attacks
(provided the enrollment server uses strict rate limiting policies).
The second property deters but does not completely prevent Eclipse
attacks. Because an Eclipse attacker must impersonate peers on the
other side of the attacker, he must have a certificate for suitable
peer IDs, which requires him to repeatedly query the enrollment
server for new certificates which only will match by chance. From
the attacker's perspective, the difficulty is that if he only has a
small number of certificates the region of the Overlay Instance he
is impersonating appears to be very sparsely populated by comparison
to the victim's local region.In general, whenever a peer engages in overlay activity that
might affect the routing table it must establish its identity. This
happens in two ways. First, whenever a peer establishes a direct
connection to another peer it authenticates via certificate-based
mutual authentication. All messages between peers are sent over this
protected channel and therefore the peers can verify the data origin
of the last hop peer for requests and responses without further
cryptography.In some situations, however, it is desirable to be able to
establish the identity of a peer with whom one is not directly
connected. The most natural case is when a peer Updates its state.
At this point, other peers may need to update their view of the
overlay structure, but they need to verify that the Update message
came from the actual peer rather than from an attacker. To prevent
this, all overlay routing messages are signed by the peer that
generated them.[OPEN ISSUE: this allows for replay attacks on requests. There
are two basic defenses here. The first is global clocks and loose
anti-replay. The second is to refuse to take any action unless you
verify the data with the relevant node. This issue is
undecided.][TODO: I think we are probably going to end up with generic
signatures or at least optional signatures on all overlay
messages.]The goal here is to stop an attacker from knowing who is
signaling what to whom. An attacker being able to observe the
activities of a specific individual is unlikely given the
randomization of IDs and routing based on the present peers
discussed above. Furthermore, because messages can be routed using
only the header information, the actual body of the RELOAD message
can be encrypted during transmission.There are two lines of defense here. The first is the use of TLS
or DTLS for each communications link between peers. This provides
protection against attackers who are not members of the overlay. The
second line of defense, if certificate-based security is used, is to
digitally sign each message. This prevents adversarial peers from
modifying messages in flight, even if they are on the routing
path.The routing security mechanisms in RELOAD are designed to contain
rather than eliminate attacks on routing. It is still possible for
an attacker to mount a variety of attacks. In particular, if an
attacker is able to take up a position on the overlay routing
between A and B it can make it appear as if B does not exist or is
disconnected. It can also advertise false network metrics in attempt
to reroute traffic. However, these are primarily DoS attacks.The certificate-based security scheme secures the namespace, but
if an individual peer is compromised or if an attacker obtains a
certificate from the CA, then a number of subversive peers can still
appear in the overlay. While these peers cannot falsify responses to
resource queries, they can respond with error messages, effecting a
DoS attack on the resource registration. They can also subvert
routing to other compromised peers. To defend against such attacks,
a resource search must still consist of parallel searches for
replicated registrations.This section contains the new code points registered by this
document. [NOTE TO IANA/RFC-EDITOR: Please replace RFC-AAAA with the RFC
number for this specification in the following list.]IANA has already allocated a port for the main peer to peer
protocol. This port has the name p2p-sip and the port number of 6084.
The names of this port may need to be changed as this draft progresses
and if it does careful instructions will be needed to IANA to ensure
the final RFC and IANA registrations are in sync.[[TODO - add IANA registration for p2p_enroll SRV and
p2p_menroll]]IANA SHALL create a "RELOAD Overlay Algorithm Type" Registry.
Entries in this registry are strings denoting the names of overlay
algorithms. The registration policy for this registry is RFC 5226 IETF
Review. The initial contents of this registry are:Algorithm NameRFCchord-128-2-16+RFC-AAAAIANA SHALL create a "RELOAD Access Control Policy" Registry.
Entries in this registry are strings denoting access control policies,
as described in . New entries
in this registry SHALL be registered via RFC 5226 IETF Review. The
initial contents of this registry are:USER-MATCHNODE-MATCHUSER-NODE-MATCHNODE-MULTIPLEUSER-MATCH-WITH-ANONYMOUS-CREATEIANA SHALL create a "RELOAD Data Kind-ID" Registry. Entries in this
registry are 32-bit integers denoting data kinds, as described in
. Code points in the range 0x00000001
to 0x7fffffff SHALL be registered via RFC 5226 Standards Action. Code
points in the range 0x8000000 to 0xf0000000 SHALL be registered via
RFC 5226 Expert Review. Code points in the range 0xf0000001 to
0xffffffff are reserved for private use via the kind description
mechanism described in . The
initial contents of this registry are:KindKind-IDRFCINVALID0RFC-AAAASIP-REGISTRATION1RFC-AAAATURN_SERVICE2RFC-AAAACERTIFICATE3RFC-AAAAROUTING_TABLE_SIZE4RFC-AAAASOFTWARE_VERSION5RFC-AAAAMACHINE_UPTIME6RFC-AAAAAPP_UPTIME7RFC-AAAAMEMORY_FOOTPRINT8RFC-AAAADATASIZE_StoreD9RFC-AAAAINSTANCES_StoreD10RFC-AAAAMESSAGES_SENT_RCVD11RFC-AAAAEWMA_BYTES_SENT12RFC-AAAAEWMA_BYTES_RCVD13RFC-AAAALAST_CONTACT14RFC-AAAARTT15RFC-AAAAReserved0x7fffffffRFC-AAAAReserved0xffffffffRFC-AAAAIANA SHALL create a "RELOAD Data Model" Registry. Entries in this
registry are 8-bit integers denoting data models, as described in
. Code points in this registry
SHALL be registered via RFC 5226 IETF Review. The initial contents of
this registry are:Data ModelCodeRFCINVALID0RFC-AAAASINGLE_VALUE1RFC-AAAAARRAY2RFC-AAAADICTIONARY3RFC-AAAARESERVED255RFC-AAAAIANA SHALL create a "RELOAD Message Code" Registry. Entries in this
registry are 16-bit integers denoting method codes as described in
. These codes SHALL be registered
via RFC 5226 Standards Action. The initial contents of this registry
are:Message Code NameCode ValueRFCinvalid0RFC-AAAAprobe_req1RFC-AAAAprobe_ans2RFC-AAAAattach_req3RFC-AAAAattach_ans4RFC-AAAAunused5unused6store_req7RFC-AAAAstore_ans8RFC-AAAAfetch_req9RFC-AAAAfetch_ans10RFC-AAAAremove_req11RFC-AAAAremove_ans12RFC-AAAAfind_req13RFC-AAAAfind_ans14RFC-AAAAjoin_req15RFC-AAAAjoin_ans16RFC-AAAAleave_req17RFC-AAAAleave_ans18RFC-AAAAupdate_req19RFC-AAAAupdate_ans20RFC-AAAAroute_query_req21RFC-AAAAroute_query_ans22RFC-AAAAping_req23RFC-AAAAping_ans24RFC-AAAAstat_req25RFC-AAAAstat_ans26RFC-AAAAattachlite_req27RFC-AAAAattachlite_ans28RFC-AAAAreserved0x8000..0xfffeRFC-AAAAerror0xffffRFC-AAAAIANA SHALL create a "RELOAD Error Code" Registry. Entries in this
registry are 16-bit integers denoting error codes. New entries SHALL
be defined via RFC 5226 Standards Action. The initial contents of this
registry are:Error Code NameCode ValueRFCinvalid0RFC-AAAAError_Unauthorized1RFC-AAAAError_Forbidden2RFC-AAAAError_Not_Found3RFC-AAAAError_Request_Timeout4RFC-AAAAError_Precondition_Failed5RFC-AAAAError_Incompatible_with_Overlay6RFC-AAAAError_Unsupported_Forwarding_Option7RFC-AAAAError_Data_Too_Large8RFC-AAAAError_Data_Too_Old9RFC-AAAAError_TTL_Exceeded10RFC-AAAAError_Message_Too_Large11RFC-AAAAreserved0x8000..0xfffeRFC-AAAAIANA SHALL create a "RELOAD Route Log Extension Type Registry." New
entries SHALL be defined via RFC 5226 Specification Required. The
initial contents of this registry are:Route Log Extension NameCodeSpecificationinvalid0RFC-AAAAreserved255RFC-AAAAIANA shall create a "RELOAD Overlay Link Type Registry." New
entries SHALL be defined via RFC 5226 Standards Action. This registry
SHALL be initially populated with the following values:ProtocolCodeSpecificationinvalid0RFC-AAAAtcp_tls1RFC-AAAAudp_dtls2RFC-AAAAreserved255RFC-AAAAIANA shall create a "Forwarding Option Registry". Entries in this
registry between 1 and 127 SHALL be defined via RFC 5226 Standards
Action. Entries in this registry between 128 and 254 SHALL be defined
via RFC 5226 Specification Required. This registry SHALL be initially
populated with the following values:Forwarding OptionCodeSpecificationinvalid0RFC-AAAAreserved255RFC-AAAAIANA shall create a "RELOAD Probe Information Type Registry".
Entries in this registry SHALL be defined via RFC 5226 Standards
Action. This registry SHALL be initially populated with the following
values:Probe OptionCodeSpecificationinvalid0RFC-AAAAresponsible_set1RFC-AAAArequested_info2RFC-AAAAreserved255RFC-AAAAThis section describes the scheme for a reload: URI, which can be
used to refer to either:A peer.A resource inside a peer.The reload: URI is defined using a subset of the URI schema
specified in Appendix A of RFC 3986 [REF] and the associated URI
Guidelines [REF: RFC4395] per the following ABNF syntax:The definitions of these productions are as follows:a hex-encoded Destination List
object.the name of the overlay.a hex-encoded StoredDataSpecifier
indicating the data element.If no specifier is present than this URI addresses the peer which
can be reached via the indicated destination list at the indicated
overlay name. If a specifier is present, then the URI addresses the
data value.The following summarizes the information necessary to register
the reload: URI.reloadpermanentsee .The reload: URI is intended
to be used as a reference to a RELOAD peer or resource.The reload: URI is not
intended to be human-readable text, therefore they are encoded
entirely in US-ASCII.The
RELOAD protocol described in RFC-AAAA.TBD for the rest of this template.This draft is a merge of the "REsource LOcation And Discovery
(RELOAD)" draft by David A. Bryan, Marcia Zangrilli and Bruce B.
Lowekamp, the "Address Settlement by Peer to Peer" draft by Cullen
Jennings, Jonathan Rosenberg, and Eric Rescorla, the "Security
Extensions for RELOAD" draft by Bruce B. Lowekamp and James Deverick,
the "A Chord-based DHT for Resource Lookup in P2PSIP" by Marcia
Zangrilli and David A. Bryan, and the Peer-to-Peer Protocol (P2PP) draft
by Salman A. Baset, Henning Schulzrinne, and Marcin Matuszewski. Thanks
to the authors of RFC 5389 for text included from that.Thanks to the many people who contributed including: Michael Chen,
TODO - fill in.A SIP Usage for RELOADThis document defines REsource LOcation And Discovery (RELOAD),
a peer-to-peer (P2P) signaling protocol for use on the Internet. A
P2P signaling protocol provides its clients with an abstract
storage and messaging service between a set of cooperating peers
that form the overlay network. RELOAD is designed to support a P2P
Session Initiation Protocol (P2PSIP) network, but can be utilized
by other applications with similar requirements by defining new
usages that specify the kinds of data that must be stored for a
particular application. RELOAD defines a security model based on a
certificate enrollment service that provides unique identities.
NAT traversal is a fundamental service of the protocol. RELOAD
also allows access from "client" nodes which do not need to route
traffic or store data for others.The Sybil AttackMicrosoft ResearchEclipse Attacks on Overlay Networks: Threats and
DefensesNon-Transitive Connectivity and DHTsAnalytical Study on Improving DHT Lookup Performance under
ChurnThe Design of a Versatile, Secure P2PSIP Communications
Architecture for the Public InternetOpenDHT: A Public DHT and its UsesChord: A Scalable Peer-to-peer Lookup Protocol for Internet
ApplicationsMIT Laboratory for Computer ScienceMIT Laboratory for Computer ScienceMIT Laboratory for Computer ScienceMIT Laboratory for Computer ScienceMIT Laboratory for Computer ScienceMIT Laboratory for Computer ScienceMIT Laboratory for Computer ScienceVulnerabilities and Security Threats in Structured
Peer-to-Peer Systems: A Quantitative AnalysisHandling Churn in a DHTMinimizing Churn in Distributed SystemsAdded the ability to introduce new kinds dynamically.Added configuration file updating.Major revisions to reliability and flow control algorithms.Moved diagnostics out--they no go in a separate draft.Removed REMOVE: you now store a "nonexistent" element.Split base protocol from combined draft into new draft.Update architecture discussion to address concerns raised about
clarity of roles.Moved extensive discussion of routing and client behaviors to
appendix.Split Ping into Ping and ProbeAdded AttachLite to provide way to implement ICE-Liteadded Stat call for retrieving meta-dataadded discussion of periodic vs reactive recovery issuechanged finger table stabilization to prefer long-lived over
best-matchupdated IANA considerations to be more completechanged error codes from http-basedremoved TUNNEL methodallow implementations more flexibility in picking finger table
entry and revise random rangedecouple overlay configuration from enrollment serveradd error for data too largechange architecture to overlay perspective from previous
revision and update terminology in document to matchreordered message routing section to clarify that other routing
algorithms are possible besides symmetric recursive.clarified document IPR termsFragment offset was too small to hold 2^24 bit messages so
fixed this from 16 bits to 32 bits.Changed absolute times from seconds to millisecondsAdded error for messages over max sizeAdded error for TTL expiredAdd time in response to PINGClarified retransmission and fragmentation algorithmClarified acknowledgement tracking for congestion controlSignificant discussion has been focused on the selection of a routing
algorithm for P2PSIP. This section discusses the motivations for
selection of symmetric recursive routing for RELOAD and describes the
extensions that would be required to support additional routing
algorithms.Iterative routing has a number of advantages. It is easier to
debug, consumes fewer resources on intermediate peers, and allows the
querying peer to identify and route around misbehaving peers . However, in the
presence of NATs iterative routing is intolerably expensive because a
new connection must be established for each hop (using ICE) .Iterative routing is supported through the Route_Query mechanism
and is primarily intended for debugging. It is also allows the
querying peer to evaluate the routing decisions made by the peers at
each hop, consider alternatives, and perhaps detect at what point the
forwarding path fails.An alternative to the symmetric recursive routing method used by
RELOAD is Forward-Only routing, where the response is routed to the
requester as if it is a new message initiating by the responder (in
the previous example, Z sends the response to A as if it were sending
a request). Forward-only routing requires no state in either the
message or intermediate peers.The drawback of forward-only routing is that it does not work when
the overlay is unstable. For example, if A is in the process of
joining the overlay and is sending a Join request to Z, it is not yet
reachable via forward routing. Even if it is established in the
overlay, if network failures produce temporary instability, A may not
be reachable (and may be trying to stabilize its network connectivity
via Attach messages).Furthermore, forward-only responses are less likely to reach the
querying peer than symmetric recursive because the forward path is
more likely to have a failed peer than the request path (which was
just tested to route the request) .An extension to RELOAD that supports forward-only routing but
relies on symmetric responses as a fallback would be possible, but due
to the complexities of determining when to use forward-only and when
to fallback to symmetric, we have chosen not to include it as an
option at this point.Another routing option is Direct Response routing, in which the
response is returned directly to the querying node. In the previous
example, if A encodes its IP address in the request, then Z can simply
deliver the response directly to A. In the absence of NATs or other
connectivity issues, this is the optimal routing technique.The challenge of implementing direct response is the presence of
NATs. There are a number of complexities that must be addressed. In
this discussion, we will continue our assumption that A issued the
request and Z is generating the response.The IP address listed by A may be unreachable, either due to
NAT or firewall rules. Therefore, a direct response technique must
fallback to symmetric response . The hop-by-hop ACKs
used by RELOAD allow Z to determine when A has received the
message (and the TLS negotiation will provide earlier confirmation
that A is reachable), but this fallback requires a timeout that
will increase the response latency whenever A is not reachable
from Z.Whenever A is behind a NAT it will have multiple candidate IP
addresses, each of which must be advertised to ensure
connectivity, therefore Z will need to attempt multiple
connections to deliver the response.One (or all) of A's candidate addresses may route from Z to a
different device on the Internet. In the worst case these nodes
may actually be running RELOAD on the same port. Therefore,
establishing a secure connection to authenticate A before
delivering the response is absolutely necessary. This step
diminishes the efficiency of direct response because multiple
roundtrips are required before the message can be delivered.If A is behind a NAT and does not have a connection already
established with Z, there are only two ways the direct response
will work. The first is that A and Z are both behind the same NAT,
in which case the NAT is not involved. In the more common case,
when Z is outside A's NAT, the response will only be received if
A's NAT implements endpoint-independent filtering. As the choice
of filtering mode conflates application transparency with security
, and no clear recommendation is
available, the prevalence of this feature in future devices
remains unclear.An extension to RELOAD that supports direct response routing but
relies on symmetric responses as a fallback would be possible, but due
to the complexities of determining when to use direct response and
when to fallback to symmetric, and the reduced performance for
responses to peers behind restrictive NATs, we have chosen not to
include it as an option at this point.SEP has proposed
implementing a form of direct response by having A identify a peer, Q,
that will be directly reachable by any other peer. A uses Attach to
establish a connection with Q and advertises Q's IP address in the
request sent to Z. Z sends the response to Q, which relays it to A.
This then reduces the latency to two hops, plus Z negotiating a secure
connection to Q.This technique relies on the relative population of nodes such as A
that require relay peers and peers such as Q that are capable of
serving as a relay peer. It also requires nodes to be able to identify
which category they are in. This identification problem has turned out
to be hard to solve and is still an open area of exploration.An extension to RELOAD that supports relay peers is possible, but
due to the complexities of implementing such an alternative, we have
not added such a feature to RELOAD at this point.A concept similar to relay peers, essentially choosing a relay peer
at random, has previously been suggested to solve problems of pairwise
non-transitivity ,
but deterministic filtering provided by NATs make random relay peers
no more likely to work than the responding peer.A common concern about symmetric recursive routing has been that
one or more peers along the request path may fail before the response
is received. The significance of this problem essentially depends on
the response latency of the overlay. An overlay that produces slow
responses will be vulnerable to churn, whereas responses that are
delivered very quickly are vulnerable only to failures that occur over
that small interval.The other aspect of this issue is whether the request itself can be
successfully delivered. Assuming typical connection maintenance
intervals, the time period between the last maintenance and the
request being sent will be orders of magnitude greater than the delay
between the request being forwarded and the response being received.
Therefore, if the path was stable enough to be available to route the
request, it is almost certainly going to remain available to route the
response.An overlay that is unstable enough to suffer this type of failure
frequently is unlikely to be able to support reliable functionality
regardless of the routing mechanism. However, regardless of the
stability of the return path, studies show that in the event of high
churn, iterative routing is a better solution to ensure request
completion Finally, because RELOAD retries the end-to-end request, that retry
will address the issues of churn that remain.There are a wide variety of reasons a node may act as a client rather
than as a peer . This
section outlines some of those scenarios and how the client's behavior
changes based on its capabilities.For a number of reasons, a particular node may be forced to act as
a client even though it is willing to act as a peer. These
include:The node does not have appropriate network connectivity,
typically because it has a low-bandwidth network connection.The node may not have sufficient resources, such as computing
power, storage space, or battery power.The overlay algorithm may dictate specific requirements for
peer selection. These may include participation in the overlay to
determine trustworthiness, control the number of peers in the
overlay to reduce overly-long routing paths, or ensure minimum
application uptime before a node can join as a peer.The ultimate criteria for a node to become a peer are determined by
the overlay algorithm and specific deployment. A node acting as a
client that has a full implementation of RELOAD and the appropriate
overlay algorithm is capable of locating its responsible peer in the
overlay and using CONNECT to establish a direct connection to that
peer. In that way, it may elect to be reachable under either of the
routing approaches listed above. Particularly for overlay algorithms
that elect nodes to serve as peers based on trustworthiness or
population, the overlay algorithm may require such a client to locate
itself at a particular place in the overlay.SIP defines an extensive protocol for registration and security
between a client and its registrar/proxy server(s). Any SIP device can
act as a client of a RELOAD-based P2PSIP overlay if it contacts a peer
that implements the server-side functionality required by the SIP
protocol. In this case, the peer would be acting as if it were the
user's peer, and would need the appropriate credentials for that
user.Application-level support for clients is defined by a usage. A
usage offering support for application-level clients should specify
how the security of the system is maintained when the data is moved
between the application and RELOAD layers.