With-defaults capability for NETCONF
draft-ietf-netconf-with-defaults-05

Abstract

The NETCONF protocol defines ways to read configuration data from a NETCONF server. Part of this data is not set by the NETCONF client, but rather a default value is used. In many situations the NETCONF client has a priori knowledge about default data, so the NETCONF server does not need to send it to the client. In other situations the NETCONF client will need this data as part of the NETCONF <rpc-reply> messages. This document defines a capability-based extension to the NETCONF protocol that allows the NETCONF client to control whether default values are part of NETCONF <rpc-reply> messages or <copy-config> output to the target URL.

Status of this Memo

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Table of Contents

1.  Introduction
    1.1.  Terminology
    1.2.  Current handling of default data
2.  With-defaults Capability
    2.1.  Overview
    2.2.  Dependencies
    2.3.  Conformance
    2.4.  Capability Identifier
    2.5.  New Operations
    2.6.  Modifications to Existing Operations
    2.7.  Interactions with Other Capabilities
3.  YANG Module
4.  IANA Considerations
5.  Security Considerations
6.  Acknowledgements
7.  Normative References
Appendix A.  Open Issues
Appendix B.  Change Log
    B.1.  -00
    B.2.  00-01
    B.3.  01-02
    B.4.  02-03
    B.5.  03-04
    B.6.  04-05
§  Authors' Addresses

1.  Introduction

The NETCONF protocol [RFC4741] (Enns, R., “NETCONF Configuration Protocol,” December 2006.) defines ways to read configuration data from a NETCONF server. Part of this data is not set by the NETCONF client, but rather a default value is used. In many situations the NETCONF client has a priori knowledge about default data, so the NETCONF server does not need to send it to the client. A priori knowledge can be e.g., a document formally describing the data models supported by the NETCONF server.

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 client will need the default data from the node:

• The management application often needs a single, definitive and complete set of configuration values that determine how the a networking device works.
• 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 these cases the NETCONF client 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 client to control whether default data is part of NETCONF <rpc-reply> messages.

1.1.  Terminology

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 [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

Data model schema:

A document or set of documents describing the data models supported by the NETCONF server.

Management Application:

A computer program running outside the NETCONF server that configures or supervises the NETCONF server. A management application can reach the device e.g. via the NETCONF, CLI or SNMP.

Default data:

Data specified in the data model schema as default, that is set or used by the device whenever the NETCONF client or other management application/user does not provide a specific value for the relevant data item. Default data MAY or MAY NOT be stored as part of a configuration datastore.

Explicitly set data:

Data that is set to any value by a NETCONF client or other management application by the way of an actual management operation, including any data model schema default value. Any value set by the NETCONF server which is not the schema defined default value is also considered explicitly set data.

In addition the following terms are defined in RFC 4741 and are not redefined here:

• client
• operation
• RPC
• RPC request
• RPC response
• server

1.2.  Current handling of default data

NETCONF does not define whether default data is part of the datastore/data model, or if it is meta-data that influences the behavior of the NETCONF server, but is not actually part of the datastore. This document is intended to support either type of implementation, without deciding which approach is better.

As a consequence of this approach, NETCONF servers that do not implement the :with-defaults capability may or may not return default data.

Different NETCONF servers report default data in different ways. This document specifies the following three basic modes:

report-all:

All default data is always reported.

trim:

Values are not reported if they match the default value (as specified in the data model schema).

explicit:

Report only values that match the definition of explicitly set data.

2.  With-defaults Capability

2.1.  Overview

The :with-defaults capability indicates that the NETCONF server makes it possible for the NETCONF client to control whether default data is part of NETCONF <rpc-reply> messages. The capability affects both configuration and state data (while acknowledging that the usage of default values for state data is less prevalent). Sending of default data is controlled for each individual operation separately.

A NETCONF server implementing the :with-defaults capability MUST indicate its basic behavior, whether it sends default data in the absence of any specific request from the NETCONF client; and MUST support the 'report-all' handling mode and MAY support other modes.

A server indicating 'explicit' either in the basic or the also-supported parameter MUST be able to differentiate between normal default data and explicitly set data.

2.2.  Dependencies

None

2.3.  Conformance

Every NETCONF server SHOULD implement this capability.

2.4.  Capability Identifier

urn:ietf:params:netconf:capability:with-defaults:1.0

The identifier MUST have a parameter: "basic-mode". This indicates how the server reports default data in <rpc-reply> messages, in the case the client does not specify the required behavior in the <rpc> request. The allowed values of this parameter are report-all, trim, explicit as listed in Section 1.2 (Current handling of default data).

The identifier MAY have another parameter: "also-supported". This parameter indicates which additional default handling modes the server supports. The value of the parameter is a comma separated list of one or two modes that are supported beside the mode indicated in the basic parameter. Possible modes are taken from the list in Section 1.2 (Current handling of default data).

In addition to these parameters, the identifier MUST have the YANG 'module' and 'revision' parameters if the ietf-with-defaults YANG module is supported, as defined in section 5.6.4 of [I‑D.ietf‑netmod‑yang] (Bjorklund, M., “YANG - A data modeling language for NETCONF,” April 2010.).

Example:

urn:ietf:params:netconf:capability:with-defaults:1.0?module=ietf-netconf-with-defaults&revision=2010-03-05&basic-mode=report-all

urn:ietf:params:netconf:capability:with-defaults:1.0?module=ietf-netconf-with-defaults&revision=2010-03-05&basic-mode=report-all&also-supported=trim,explicit

2.5.  New Operations

None

2.6.  Modifications to Existing Operations

A new <with-defaults> XML [W3C.REC‑xml‑20001006] (Sperberg-McQueen, C., Maler, E., Paoli, J., and T. Bray, “Extensible Markup Language (XML) 1.0 (Second Edition),” October 2000.) 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 server 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 Section 1.2 (Current handling of default data). The allowed values are restricted to the values that the device indicates support for in the with-defaults capability in the basic and also-supported parameters.

If an unsupported value is used, the NETCONF server SHALL return an <rpc-reply> with an <rpc-error> element. The <error-tag> SHALL be 'operation-not-supported', and the <error-app-tag> SHALL be 'with-defaults-mode-not-supported'.

If the <with-defaults> element is not present, the server follows its basic behavior as indicated by the capability identifier's parameter see Section 2.4 (Capability Identifier).

Affected operations:

• <get>
• <get-config>
• <copy-config>

<copy-config> is only affected if the target of the operation is a URL. If the target is a NETCONF datastore (running, candidate or startup) the capability has no effect; the with-defaults parameter, if present, SHALL be silently ignored.

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-config> operation which is using the 'with-defaults' element. The client 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 server is "trim". As the 'with-defaults' element has the value 'report-all', the mtu is returned not just for eth0 but also for eth1.

    <rpc message-id="102"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <get-config>
        <source>
           <running/>
        </source>
        <filter type="subtree">
          <interfaces xmlns="http://example.com/interfaces/1.2"/>
        </filter>
        <with-defaults
          xmlns="urn:ietf:params:netconf:capability:with-defaults:1.0">
          report-all
        </with-defaults>
      </get-config>
    </rpc>

    <rpc-reply message-id="102"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <data>
        <interfaces xmlns="http://example.com/interfaces/1.2">
          <interface>
            <name>eth0</name>
            <mtu>8192</mtu>
          </interface>
          <interface>
            <name>eth1</name>
            <mtu>1500</mtu>
          </interface>
        </interfaces>
      </data>
    </rpc-reply>

2.7.  Interactions with Other Capabilities

None

3.  YANG Module

The following YANG module defines the addition of the with-defaults element to the <get>, <get-config> and <copy-config> operations. The YANG language is defined in [I‑D.ietf‑netmod‑yang] (Bjorklund, M., “YANG - A data modeling language for NETCONF,” April 2010.). The above operations are defined in YANG in [I‑D.ietf‑netconf‑4741bis] (Enns, R., Bjorklund, M., Schoenwaelder, J., and A. Bierman, “Network Configuration Protocol (NETCONF),” February 2010.). Every NETCONF server SHOULD implement this YANG module.

-- RFC Ed.: Insert license information for code as appropriate

<CODE BEGINS> file="ietf-netconf-with-defaults.yang"

module ietf-netconf-with-defaults {

   namespace "urn:ietf:params:netconf:capability:with-defaults:1.0";

   prefix nwd;

   import ietf-netconf { prefix nc; }

   organization
    "IETF NETCONF (Network Configuration Protocol) Working Group";

   contact
    "WG Web:   <http://tools.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>

     WG Chair: Bert Wijnen
               <mailto:bertietf@bwijnen.net>

     WG Chair: Mehmet Ersue
               <mailto:mehmet.ersue@nsn.com>

     Editor: Andy Bierman
             <mailto:andyb@iwl.com>

     Editor: Balazs Lengyel
             <mailto:balazs.lengyel@ericsson.com>";

   description
    "This module defines a capability-based extension to the
     NETCONF protocol that allows the NETCONF client to control
     whether default values are part of NETCONF
     <rpc-reply> messages or <copy-config> output to the target URL.


     Copyright (c) 2010 IETF Trust and the persons identified as
     the document authors.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject
     to the license terms contained in, the Simplified BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (http://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX; see
     the RFC itself for full legal notices.";
   // RFC Ed.: replace XXXX with actual RFC number and remove this note

   // RFC Ed.: remove this note
   // Note: extracted from draft-ietf-netmod-with-defaults-05.txt

   revision 2010-03-05 {
     description
       "Initial version.";
     reference
      "RFC XXXX: With-defaults capability for NETCONF";
   }
   // RFC Ed.: replace XXXX with actual RFC number and remove this note

   typedef with-defaults-mode {
      description
        "Possible modes to report default data in
         rpc-reply messages.";
      type enumeration {
         enum report-all {
             description
               "All default data is always reported.";
         }
         enum trim {
             description
               "Values are not reported if they match the default.";
         }
         enum explicit {
             description
               "Report values that match the definition of
                explicitly set data.";
         }
     }
   }

   grouping with-defaults-parameters {
     leaf with-defaults {
       description
         "The explicit defaults processing mode requested.";
       type with-defaults-mode;
     }
   }

   // extending the get-config operation
   augment /nc:get-config/nc:input {
       uses with-defaults-parameters;
   }

   // extending the get operation
   augment /nc:get/nc:input {
       uses with-defaults-parameters;
   }

   // extending the copy-config operation
   augment /nc:copy-config/nc:input {
       uses with-defaults-parameters;
   }

}

<CODE ENDS>

4.  IANA Considerations

This document registers one capability identifier URN from the 'Network Configuration Protocol [RFC4741] (Enns, R., “NETCONF Configuration Protocol,” December 2006.) Capability URNs' registry, and registers the same URN for the NETCONF XML namespace in the "IETF XML registry" [RFC3688] (Mealling, M., “The IETF XML Registry,” January 2004.). Note that the capability URN is compliant to [RFC4741] (Enns, R., “NETCONF Configuration Protocol,” December 2006.) section 10.3.

5.  Security Considerations

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 gives client control 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.

6.  Acknowledgements

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

7. Normative References

Appendix A.  Open Issues

This section will be removed. The open issues are closed in this revision of the draft, pending working group approval.

Is the definition of defaults OK? [The definition of explicitly set default data has been changed to 'explicitly set data', and now aligns with the YANG definition.]

Shall we wait for YANG and 4741bis and make the YANG normative? [Yes.]

Shall we make with-defaults mandatory? [No. It is SHOULD, not MUST.]

Appendix B.  Change Log

-- RFC Ed.: remove this section before publication.

B.1.  -00

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.

B.2.  00-01

Changed value set of with-default capability and element

Added version to URI

B.3.  01-02

report-all made mandatory

Placeholder for YAM added, XSD will be removed when 4741 provides the NETCONF YAM

with-defaults is valid for state data as well (if state data has a defined default which might not be so frequent). The definition of explicit was modified for state data.

B.4.  02-03

Clarifications

YAM added

Use the same URN for the capability and the XML namespace to accommodate YANG, and avoid two separate URN/URIs being advertised in the HELLO message, for such a small function.

B.5.  03-04

Clarifications

Added non-netconf interfaces to the definition of explicitly set default data

B.6.  04-05

Updated I-D and YANG module boiler-plate.

Removed redundant 'with-defaults' YANG feature.

Changed definition of 'explicit' mode to match the YANG definition

Removed XSD because the YANG is normative and the XSD is unconstrained, and does not properly extend the 3 affected NETCONF operations.

Made the YANG module a normative section instead of non-normative appendix.

Changed YANG from an informative to a normative reference,

Changed 4741bis from an informative to a normative reference because the YANG module imports the ietf-netconf module in order to augment some RPC operations.

Updated capability requirements to include YANG module capability parameters.

Added a description statement to the with-defaults leaf definition.

Update open issues section; ready to close all open issues.

Authors' Addresses