With-defaults capability for NETCONF

The NETCONF protocol defines ways to read configuration data from a NETCONF agent. Part of this data is not set by the NETCONF manager, but rather a default value is used. In many situations the NETCONF manager has a priori knowledge about default data, so the NETCONF agent does not need to send it to the manager. A priori knowledge can be e.g. a document formally describing the data models supported by the NETCONF agent. A networking device may have a large number of default values. Often the default values are not interesting or specifically defined with a "reasonable" value, so that the management user does not have to handle them. For these reasons it is quite common for networking devices to suppress the output of parameters having the default value. However there are use-cases when a NETCONF manager will need the default data from the node: Documentation about default values can be unreliable or unavailable. Some management applications might not have the capabilities to correctly parse and interpret formal data models. Human users might want to understand the received data without consultation of the documentation. In all theses cases the NETCONF manager will need default data as part of the NETCONF <rpc-reply> messages. This document defines a capability-based extension to the NETCONF protocol that allows the NETCONF manager to control whether default data is part of NETCONF <rpc-reply> messages.

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 .

Default data: Data that is set or used by the NETCONF agent whenever the NETCONF manager does not provide a specific value for the relevant data item. Default values are often specified in documents describing the data models supported by the NETCONF agent. In the context of this document only configuration data is considered, state data is excluded. Explicitly set default data: Data that is explicitly set by the NETCONF manager to it's default value. Some agents MIGHT treat explicitly set default data as simple default data, as they MIGHT not be able to differentiate between them. In addition the following terms are defined in RFC 4741 and are not redefined here: agent application manager operation RPC RPC request RPC response

The :with-defaults capability indicates that the NETCONF agent makes it possible for the NETCONF manager to control whether default data is part of NETCONF <rpc-reply> messages. The capability only affects configuration data not state data. Sending of default data is controlled for each individual operation separately. The NETCONF agent MUST also indicate its basic behavior, whether it sends default data in the absence of any specific request from the NETCONF manager.

It is not defined in , whether default data is part of the datastore/data model, or if it is meta data, that influences the behavior of the NETCONF server, device but is not actually part of the datastore. This document intentionally avoids deciding this question. As a consequence of this issue, NETCONF servers that do not implement the :with-defaults capability may or may not return default data in NETCONF <rpc-reply> messages. Different NETCONF agents report default data in different ways. This document specifies the following three basic methods: Report all: All default data is always reported. Trim: Values are not reported if they match the default. Explicit: Report values if they are explicitly set.

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urn:ietf:params:netconf:capability:with-defaults:1.0 The identifier MUST have a parameter: "basic". This indicates how the agent reports default data in <rpc-reply> messages, in the case the manager does not specify the required behavior in the <rpc> request. The allowed values of this parameter are report-all, trim, explicit as listed in . The identifier MAY have another parameter: "supported". This indicates what other default handling methods does the agent support. The value of the parameter is a colon separated list of one or two supported methods. Possible methods are taken from the list in . Example: urn:ietf:params:netconf:capability:with-defaults:1.0?basic=report-all urn:ietf:params:netconf:capability:with-defaults:1.0?basic=report-all&supported=trim:explicit

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A new <with-defaults> XML child element is added to the 'method-name' element. This is the element that indicates the type of the operation e.g. <get>, <get-config> or <copy-config>. If the <with-defaults> element is present, it controls the reporting of default data. The agent MUST return default data in the NETCONF <rpc-reply> messages according to the value of the element. Allowed values of the with-defaults element are taken from the list in . The allowed values are restricted to the values that the device indicates support for in the with-defaults capability. If the <with-defaults> element is not present, the agent follows its basic behavior as indicated by the capability identifier's parameter see . Affected operations: <get> <get-config> <copy-config> Other operations that return configuration data SHOULD also handle default data according to the rules set in this document, and explicitly state this in their documentation. If this is not specified in the document defining the respective operation, the default handling rules described herein do not affect these operations. The following example shows a <get> operation which is using the 'with-defaults' element. The manager is retrieving the 'interfaces' object, defined in the example.com data model. (In this simple example, the 'name' field is defined as the key, and the 'mtu' field is the only other data in the <interface> element). The default value of mtu is '1500'. The basic default handling for the agent is "trim". As the 'with-defaults' element has the value 'report-all', the mtu is returned not just for eth0 but also for eth1.

report-all

eth0 8192 eth1 1500 ]]>

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This section contains an XML Schema Definition which defines the XML syntax associated for the with-defaults XML element.

Schema defining the with-defaults element. Organization: "IETF NETCONF Working Group" Contact Info: balazs.lengyel@ericsson.com ]]>

This document registers two URIs for the NETCONF XML namespace in the IETF XML registry . Note that the capability URN is compliant to section 10.3. Index Capability Identifier :with-defaults urn:ietf:params:netconf:capability:with-defaults:1.0 URI: urn:ietf:params:xml:ns:netconf:with-defaults:1.0 Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace.

This document defines a minor extension to existing NETCONF protocol operations. it does not introduce any new or increased security risks into the management system. The 'with-defaults' capability provides manager controls over the retrieval of particular types of XML data from a configuration database. They only suppress data that can already be retrieved with the standard protocol operations, and do not add any data to the configuration database.

Are there any other basic default handling methods out there we need to include?

Is the XSD needed? Does it add any value, any clarity to the document?

Changed value set of with-default capability and element Added version to URI

Created from draft-bierman-netconf-with-defaults-01.txt It was decided by the NETCONF mailing list, that with-defaults should be a sub-element of each affected operation. While this violates the XSD of RFC4741 this is acceptable and follows the ideas behind NETCONF and YANG. Hopefully it will be clarified in the 4741bis RFC whether such extensions are allowed.

Thanks to Martin Bjorklund, Sharon Chisholm, Phil Shafer, Juergen Schoenwaelder and many other members of the NETCONF WG for providing important input to this document.