RFC 9194 | YANG Module for IS-IS Reverse Metric | October 2022
Hopps | Standards Track | [Page]

Stream:
  Internet Engineering Task Force (IETF)
RFC:
  9194
Category:
  Standards Track
Published:
  October 2022
ISSN:
  2070-1721
Author:
  C. Hopps
  LabN Consulting, L.L.C.

# RFC 9194

# A YANG Module for IS-IS Reverse Metric

## Abstract

This document defines a YANG module for managing the reverse metric extension to the Intermediate System to Intermediate System (IS-IS) intra-domain routing information exchange protocol.¶

## Status of This Memo

This is an Internet Standards Track document.¶

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9194.¶

## Copyright Notice

Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.¶

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

## 1. Introduction

This document defines a YANG module for managing the reverse metric extension to IS-IS [RFC8500] [ISO-10589]. Please refer to [RFC8500] for the description and definition of the functionality managed by this module.¶

The YANG data model described in this document conforms to the Network Management Datastore Architecture defined in [RFC8342].¶

## 2. YANG Management

### 2.1. YANG Tree

The following is the YANG tree diagram [RFC8340] for the IS-IS reverse metric extension additions.¶

    module: ietf-isis-reverse-metric
      augment /rt:routing/rt:control-plane-protocols
                /rt:control-plane-protocol/isis:isis:
        +--rw reverse-metric
           +--rw enable-receive?   boolean
      augment /rt:routing/rt:control-plane-protocols
                /rt:control-plane-protocol/isis:isis/isis:interfaces
                /isis:interface:
        +--rw reverse-metric
           +--rw metric?              isis:wide-metric
           +--rw flags
           |  +--rw whole-lan?           boolean
           |  +--rw allow-unreachable?   boolean
           +--rw exclude-te-metric?   boolean
           +--rw level-1
           |  +--rw metric?              isis:wide-metric
           |  +--rw flags
           |  |  +--rw whole-lan?           boolean
           |  |  +--rw allow-unreachable?   boolean
           |  +--rw exclude-te-metric?   boolean
           +--rw level-2
              +--rw metric?              isis:wide-metric
              +--rw flags
              |  +--rw whole-lan?           boolean
              |  +--rw allow-unreachable?   boolean
              +--rw exclude-te-metric?   boolean
      augment /rt:routing/rt:control-plane-protocols
                /rt:control-plane-protocol/isis:isis/isis:interfaces
                /isis:interface/isis:adjacencies/isis:adjacency:
        +--ro reverse-metric
           +--ro metric?      isis:wide-metric
           +--ro flags
           |  +--ro whole-lan?           boolean
           |  +--ro allow-unreachable?   boolean
           +--ro te-metric?   uint32

¶

### 2.2. YANG Module

The following is the YANG module for managing the IS-IS reverse metric functionality defined in [RFC8500]. It imports modules from [RFC8349] and [RFC9130].¶

This YANG module uses the same per-level hierarchical configuration structure as that defined in the augmented base module.¶

    <CODE BEGINS> file "ietf-isis-reverse-metric@2022-10-19.yang"

    module ietf-isis-reverse-metric {
      yang-version 1.1;
      namespace "urn:ietf:params:xml:ns:yang:ietf-isis-reverse-metric";
      prefix isis-rmetric;

      import ietf-routing {
        prefix rt;
        reference
          "RFC 8349: A YANG Data Model for Routing Management
                     (NMDA Version)";
      }
      import ietf-isis {
        prefix isis;
        reference
          "RFC 9130: YANG Data Model for the IS-IS Protocol";
      }

      organization
        "IETF LSR Working Group (LSR)";

      contact
        "WG Web:  <https://datatracker.ietf.org/wg/lsr/>
         WG List: <mailto:lsr@ietf.org>

         Author:  Christian Hopps
                  <mailto:chopps@chopps.org>";

      description
        "This module defines the configuration and operational state
         for managing the IS-IS reverse metric functionality
         (RFC 8500).

         Copyright (c) 2022 IETF Trust and the persons identified as
         authors of the code.  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 Revised BSD License set
         forth in Section 4.c of the IETF Trust's Legal Provisions
         Relating to IETF Documents
         (https://trustee.ietf.org/license-info).

         This version of this YANG module is part of RFC 9194; see the
         RFC itself for full legal notices.";
      reference
        "RFC 8500: IS-IS Routing with Reverse Metric";

      revision 2022-10-19 {
        description
          "Initial revision.";
        reference
          "RFC 9194: A YANG Module for IS-IS Reverse Metric";
      }

      grouping reverse-metric-data {
        description
          "IS-IS reverse metric data.";
        leaf metric {
          type isis:wide-metric;
          description
            "The reverse metric value.";
          reference
            "RFC 8500: IS-IS Routing with Reverse Metric, Section 2";
        }
        container flags {
          description
            "The reverse metric flag values.";
          leaf whole-lan {
            type boolean;
            description
              "The 'Whole LAN' bit (W bit) (RFC 8500).  If true, then
               a Designated Intermediate System (DIS) processing this
               reverse metric will add the metric value to all the
               nodes it advertises in the pseudonode Link State
               Protocol Data Unit (LSP) for this interface.
               Otherwise, it will only increment the metric for the
               advertising node in the pseudonode LSP for this
               interface.";
            reference
              "RFC 8500: IS-IS Routing with Reverse Metric,
                         Section 2";
          }
          leaf allow-unreachable {
            type boolean;
            description
              "The 'Unreachable' bit (U bit) (RFC 8500).  If true, it
               allows the neighbor to increment the overall metric up
               to 2^24-1 rather than the lesser maximum of 2^24-2.
               If the metric is then set by the neighbor to 2^24-1,
               it will cause traffic to stop using, rather than avoid
               using, the interface.";
            reference
              "RFC 8500: IS-IS Routing with Reverse Metric,
                         Section 2";
          }
        }
      }

      grouping reverse-metric-if-config-data {
        description
          "IS-IS reverse metric config data.";
        uses reverse-metric-data;
        leaf exclude-te-metric {
          type boolean;
          default "false";
          description
            "If true and there is a TE metric defined for this
             interface, then do not send the Traffic Engineering
             Metric sub-TLV in the Reverse Metric TLV.";

          reference
            "RFC 8500: IS-IS Routing with Reverse Metric, Section 2";
        }
      }

      grouping tlv16-reverse-metric {
        description
          "IS-IS Reverse Metric TLV data.";
        uses reverse-metric-data;
        leaf te-metric {
          type uint32;
          description
            "The TE metric value from the sub-TLV, if present.";
          reference
            "RFC 8500: IS-IS Routing with Reverse Metric, Section 2";
        }
      }

      augment "/rt:routing/rt:control-plane-protocols/"
            + "rt:control-plane-protocol/"
            + "isis:isis" {
        when "derived-from-or-self(../rt:type, 'isis:isis')" {
          description
            "This augment is only valid when the routing protocol
             instance type is 'isis'.";
        }

        description
          "The reverse metric configuration for an IS-IS instance.";

        container reverse-metric {
          description
            "Global reverse metric configuration.";
          leaf enable-receive {
            type boolean;
            default "false";
            description
              "Enables handling of reverse metric announcements from
               neighbors.  By default, reverse metric handling is
               disabled and must be explicitly enabled through this
               configuration.";
          }
        }
      }

      augment "/rt:routing/rt:control-plane-protocols/"
            + "rt:control-plane-protocol/"
            + "isis:isis/isis:interfaces/isis:interface" {
        when "derived-from-or-self(../../../rt:type, 'isis:isis')" {
          description
            "This augment is only valid when the routing protocol
             instance type is 'isis'.";
        }

        description
          "The reverse metric configuration for an interface.";

        container reverse-metric {
          description
            "Announces a reverse metric to neighbors.  The
             configuration is hierarchical and follows the same
             behavior as that defined for per-level values in the
             augmented base module.

             Reverse metric operation is enabled by the configuration
             of a 'reverse-metric' metric value either at the top
             level or under a level-specific container node.  If a
             'reverse-metric' metric value is only specified under a
             level-specific container node, then operation is only
             enabled at the specified level.

             As the reverse metric is advertised in IS-IS Hello
             Protocol Data Units (IIH PDUs), level-specific
             configuration is only available for broadcast interface
             types.";
          uses reverse-metric-if-config-data {
            refine "flags/whole-lan" {
              default "false";
            }
            refine "flags/allow-unreachable" {
              default "false";
            }
          }
          container level-1 {
            when '../../isis:interface-type = "broadcast"';
            description
              "Announces a reverse metric to level-1 neighbors.";
            uses reverse-metric-if-config-data;
          }
          container level-2 {
            when '../../isis:interface-type = "broadcast"';
            description
              "Announces a reverse metric to level-2 neighbors.";
            uses reverse-metric-if-config-data;
          }
        }
      }
      augment "/rt:routing/rt:control-plane-protocols/"
            + "rt:control-plane-protocol/"
            + "isis:isis/isis:interfaces/isis:interface/"
            + "isis:adjacencies/isis:adjacency" {
        when "derived-from-or-self(../../../../../rt:type,
                                   'isis:isis')" {
          description
            "This augment is only valid when the routing protocol
             instance type is 'isis'.";
        }

        description
          "The reverse metric state advertised by an adjacency.";
        container reverse-metric {
          description
            "IS-IS Reverse Metric TLV data.";
          uses tlv16-reverse-metric;
        }
      }
    }

    <CODE ENDS>

¶

## 3. IANA Considerations

### 3.1. Updates to the IETF XML Registry

This document registers a URI in the "IETF XML Registry" [RFC3688]. Following the format in [RFC3688], the following registration has been made:¶

URI:
  urn:ietf:params:xml:ns:yang:ietf-isis-reverse-metric¶
Registrant Contact:
  The IESG.¶
XML:
  N/A; the requested URI is an XML namespace.¶

### 3.2. Updates to the YANG Module Names Registry

This document registers one YANG module in the "YANG Module Names" registry [RFC6020]. Following the format in [RFC6020], the following registration has been made:¶

Name:
  ietf-isis-reverse-metric¶
Maintained by IANA?
  N¶
Namespace:
  urn:ietf:params:xml:ns:yang:ietf-isis-reverse-metric¶
Prefix:
  isis-rmetric¶
Reference:
  RFC 9194¶

## 4. Security Considerations

The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].¶

The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.¶

The YANG module defined in this document can enable, disable, and modify the behavior of metrics used by routing. For the security implications regarding these types of changes, consult [RFC8500] -- which defines the functionality -- as well as [RFC9130].¶

There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These YANG nodes correspond directly to the functionality provided in RFC 8500, and the security considerations of the functionality are described in RFC 8500. These are the subtrees and data nodes:¶

    Under "/rt:routing/rt:control-plane-protocols/" +
          "rt:control-plane-protocol/isis:isis"

      - /isis-rmetric:reverse-metric/isis-rmetric:enable-receive

¶

    Under "/rt:routing/rt:control-plane-protocols/" +
          "rt:control-plane-protocol/isis:isis/" +
          "isis:interfaces/isis:interface/" +
          "isis-rmetric:reverse-metric"

      - /isis-rmetric:metric
      - /isis-rmetric:flags/isis-rmetric:whole-lan
      - /isis-rmetric:flags/isis-rmetric:allow-unreachable
      - /isis-rmetric:exclude-te-metric

¶

    Under "/rt:routing/rt:control-plane-protocols/" +
          "rt:control-plane-protocol/isis:isis/" +
          "isis:interfaces/isis:interface/" +
          "isis-rmetric:reverse-metric/" +
          "isis-rmetric:level-1/"

      - /isis-rmetric:metric
      - /isis-rmetric:flags/isis-rmetric:whole-lan
      - /isis-rmetric:flags/isis-rmetric:allow-unreachable
      - /isis-rmetric:exclude-te-metric

¶

    Under "/rt:routing/rt:control-plane-protocols/" +
          "rt:control-plane-protocol/isis:isis/" +
          "isis:interfaces/isis:interface/" +
          "isis-rmetric:reverse-metric/" +
          "isis-rmetric:level-2/"

      - /isis-rmetric:metric
      - /isis-rmetric:flags/isis-rmetric:whole-lan
      - /isis-rmetric:flags/isis-rmetric:allow-unreachable
      - /isis-rmetric:exclude-te-metric

¶

Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. These YANG nodes correspond directly to the functionality provided in RFC 8500, and the security considerations of the functionality are described in RFC 8500. These are the subtrees and data nodes:¶

    Under "/rt:routing/rt:control-plane-protocols/" +
          "rt:control-plane-protocol/isis:isis/" +
          "isis:interfaces/isis:interface/" +
          "isis:adjacencies/isis:adjacency/" +
          "isis-rmetric:reverse-metric"

      - /isis-rmetric:metric
      - /isis-rmetric:flags/isis-rmetric:whole-lan
      - /isis-rmetric:flags/isis-rmetric:allow-unreachable
      - /isis-rmetric:te-metric

¶

## 5. Normative References

[ISO-10589]
  ISO, "Intermediate System to Intermediate System intra- domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002, <https://www.iso.org/standard/30932.html>.
[RFC3688]
  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, <https://www.rfc-editor.org/info/rfc3688>.
[RFC6020]
  Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, <https://www.rfc-editor.org/info/rfc6020>.
[RFC6241]
  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, <https://www.rfc-editor.org/info/rfc6241>.
[RFC6242]
  Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, <https://www.rfc-editor.org/info/rfc6242>.
[RFC8040]
  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, <https://www.rfc-editor.org/info/rfc8040>.
[RFC8340]
  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, <https://www.rfc-editor.org/info/rfc8340>.
[RFC8341]
  Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, <https://www.rfc-editor.org/info/rfc8341>.
[RFC8342]
  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, <https://www.rfc-editor.org/info/rfc8342>.
[RFC8349]
  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for Routing Management (NMDA Version)", RFC 8349, DOI 10.17487/RFC8349, March 2018, <https://www.rfc-editor.org/info/rfc8349>.
[RFC8446]
  Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>.
[RFC8500]
  Shen, N., Amante, S., and M. Abrahamsson, "IS-IS Routing with Reverse Metric", RFC 8500, DOI 10.17487/RFC8500, February 2019, <https://www.rfc-editor.org/info/rfc8500>.
[RFC9130]
  Litkowski, S., Ed., Yeung, D., Lindem, A., Zhang, J., and L. Lhotka, "YANG Data Model for the IS-IS Protocol", RFC 9130, DOI 10.17487/RFC9130, October 2022, <https://www.rfc-editor.org/info/rfc9130>.
[W3C.REC-xml-20081126]
  Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC-xml-20081126, November 2008, <https://www.w3.org/TR/2008/REC-xml-20081126>.

## 6. Informative References

[RFC7951]
  Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, <https://www.rfc-editor.org/info/rfc7951>.

## Appendix A. Examples

### A.1. Enablement Example Using XML YANG Instance Data

Below is an example of XML [W3C.REC-xml-20081126] YANG instance data [RFC8342] to enable reverse metric processing.¶

    <rt:routing
        xmlns:rt="urn:ietf:params:xml:ns:yang:ietf-routing"
        xmlns:isis="urn:ietf:params:xml:ns:yang:ietf-isis"
        xmlns:isis-rmetric=
        "urn:ietf:params:xml:ns:yang:ietf-isis-reverse-metric">
      <rt:control-plane-protocols>
        <rt:control-plane-protocol>
          <rt:type>isis:isis</rt:type>
          <rt:name>default</rt:name>
          <isis:isis>
            <isis:area-address>00</isis:area-address>
            <isis-rmetric:reverse-metric>
         <isis-rmetric:enable-receive>true</isis-rmetric:enable-receive>
            </isis-rmetric:reverse-metric>
          </isis:isis>
        </rt:control-plane-protocol>
      </rt:control-plane-protocols>
    </rt:routing>

Figure 1: Example XML Data to Enable Reverse Metric Processing

### A.2. Usage Example Using XML YANG Instance Data

Below is an example of XML YANG instance data [RFC8342] for the "ietf-isis-reverse-metric" module.¶

    <if:interfaces
        xmlns:if="urn:ietf:params:xml:ns:yang:ietf-interfaces"
        xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">
      <if:interface>
        <if:name>eth0</if:name>
        <if:type>ianaift:ethernetCsmacd</if:type>
      </if:interface>
    </if:interfaces>
    <rt:routing
        xmlns:rt="urn:ietf:params:xml:ns:yang:ietf-routing"
        xmlns:isis="urn:ietf:params:xml:ns:yang:ietf-isis"
        xmlns:isis-rmetric=
        "urn:ietf:params:xml:ns:yang:ietf-isis-reverse-metric">
      <rt:control-plane-protocols>
        <rt:control-plane-protocol>
          <rt:type>isis:isis</rt:type>
          <rt:name>default</rt:name>
          <isis:isis>
            <isis:area-address>00</isis:area-address>
            <isis:interfaces>
              <isis:interface>
                <isis:name>eth0</isis:name>
                <isis-rmetric:reverse-metric>
                  <isis-rmetric:metric>
                    65535
                  </isis-rmetric:metric>
                </isis-rmetric:reverse-metric>
              </isis:interface>
            </isis:interfaces>
          </isis:isis>
        </rt:control-plane-protocol>
      </rt:control-plane-protocols>
    </rt:routing>

Figure 2: Example XML Data for the "ietf-isis-reverse-metric" Module

### A.3. Usage Example Using JSON YANG Instance Data

Below is an example of JSON YANG instance data [RFC7951] for the "ietf-isis-reverse-metric" module.¶

    {
      "ietf-interfaces:interfaces": {
        "interface": [
          {
            "name": "eth0",
            "type": "iana-if-type:ethernetCsmacd"
          }
        ]
      },
      "ietf-routing:routing": {
        "control-plane-protocols": {
          "control-plane-protocol": [
            {
              "type": "ietf-isis:isis",
              "name": "default",
              "ietf-isis:isis": {
                "area-address": [
                  "00"
                ],
                "interfaces": {
                  "interface": [
                    {
                      "name": "eth0",
                      "ietf-isis-reverse-metric:reverse-metric": {
                        "level-1": {
                          "metric": 65535,
                          "exclude-te-metric": true
                        }
                      }
                    }
                  ]
                }
              }
            }
          ]
        }
      }
    }

Figure 3: Example JSON Data for the Level-1-Only Reverse Metric

## Author's Address