RFC 9194 PROPOSED STANDARD ROUTING · YANG · IS-IS
IS-IS Reverse Metric YANG: A YANG Module for IS-IS Reverse Metric
A standard YANG data model for configuring and inspecting the IS-IS reverse metric feature on routers.
RFC EDITOR
Hopps, C., "A YANG Module for IS-IS Reverse Metric", RFC 9194, DOI 10.17487/RFC9194, October 2022, <https://www.rfc-editor.org/info/rfc9194>.
BIBTEX
@misc{rfc9194,
series = {Request for Comments},
number = 9194,
howpublished = {RFC 9194},
publisher = {RFC Editor},
doi = {10.17487/RFC9194},
url = {https://www.rfc-editor.org/info/rfc9194},
author = {C. Hopps},
title = {{A YANG Module for IS-IS Reverse Metric}},
pagetotal = 13,
year = 2022,
month = oct,
} RFC text
Contents
Internet Engineering Task Force (IETF) C. Hopps
Request for Comments: 9194 LabN Consulting, L.L.C.
Category: Standards Track October 2022
ISSN: 2070-1721
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.
Table of Contents
1. Introduction
2. YANG Management
2.1. YANG Tree
2.2. YANG Module
3. IANA Considerations
3.1. Updates to the IETF XML Registry
3.2. Updates to the YANG Module Names Registry
4. Security Considerations
5. Normative References
6. Informative References
Appendix A. Examples
A.1. Enablement Example Using XML YANG Instance Data
A.2. Usage Example Using XML YANG Instance Data
A.3. Usage Example Using JSON YANG Instance Data
Author's Address
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
Christian Hopps
LabN Consulting, L.L.C.
Email: chopps@chopps.org
AI ELI5
On this page
PROBLEMRFC 8500 defines a way for an IS-IS router to ask its neighbors to adjust the metric they use for a link, but there was no standard data model for configuring or viewing that feature.
MECHANISMThis RFC defines the ietf-isis-reverse-metric YANG module, which adds reverse metric settings to the IS-IS data model: a global switch for receiving, per-interface values to announce, and read-only data about what neighbors announced.
WHY IT MATTERSOperators and management systems can use NETCONF or RESTCONF to manage reverse metric in a uniform way. The module is a Proposed Standard.
§1What This Module Manages
This document defines a YANG module for managing the reverse metric extension to IS-IS. The functionality itself is described and defined in RFC 8500, so this RFC adds no new protocol behavior. It only supplies a data model for configuring and viewing it.
The model follows the Network Management Datastore Architecture defined in RFC 8342.
The feature already exists. This document only describes the settings page for it, like a remote control for a gadget someone else invented.
§2.1The YANG Tree
The module, named ietf-isis-reverse-metric, makes three augmentations to the routing model from RFC 8349 and the IS-IS model from RFC 9130.
- On the IS-IS instance, a
reverse-metriccontainer with one leaf,enable-receive. - On each IS-IS interface, a read-write
reverse-metriccontainer with ametric,flagsandexclude-te-metric, plus separatelevel-1andlevel-2copies of the same settings. - On each adjacency, a read-only
reverse-metriccontainer showing what the neighbor announced.
There are three groups of controls: one switch for the whole router, a set of dials for each link, and a read-only display showing what each neighbor asked for.
- isis (augmented)
- reverse-metric instance level
- enable-receive
- interface reverse-metric read-write
- metric
- flags: whole-lan, allow-unreachable
- exclude-te-metric
- level-1
- level-2
- adjacency reverse-metric read-only
- metric
- flags
- te-metric
- reverse-metric instance level
§2.2Receiving and Announcing Settings
Handling of reverse metric from neighbors is off by default. The leaf enable-receive defaults to false and must be explicitly enabled through configuration.
On an interface, announcing is enabled by configuring a metric value either at the top level of the container or under a level-specific container. If it is only set under a level-specific container, operation is enabled only at that level. Because the reverse metric is advertised in IS-IS Hello PDUs (IIH PDUs), the level-1 and level-2 containers are available only for broadcast interface types. The structure follows the same per-level hierarchical behavior as the augmented base module.
By default a router ignores such requests until you flip a switch. When you want to make a request yourself, you set a number on a link, and for some kinds of links you can set different numbers for the two levels of the network.
§2.3The Flags and the TE Metric
Each interface has two flags, taken from RFC 8500, both defaulting to false.
whole-lan(the W bit): if true, a Designated Intermediate System (DIS) that processes the reverse metric adds the value to all the nodes it advertises in the pseudonode LSP for the interface. Otherwise it only increments the metric for the advertising node.allow-unreachable(the U bit): if true, the neighbor may raise the overall metric up to 2^24-1 instead of the lesser maximum of 2^24-2. Setting it to 2^24-1 makes traffic stop using the interface rather than merely avoid it.
The exclude-te-metric leaf (default false) suppresses the Traffic Engineering Metric sub-TLV in the Reverse Metric TLV when a TE metric is defined. On the read-only adjacency side, a te-metric leaf of type uint32 shows the TE metric from the sub-TLV, if present.
One flag says whether the request applies to everyone on a shared link or just one router. The other says whether a neighbor may make the link so costly that nobody uses it at all.
§4Security Considerations
The module is designed to be accessed through NETCONF or RESTCONF. The mandatory-to-implement secure transport is SSH for NETCONF and TLS for RESTCONF. The Network Configuration Access Control Model (NACM) can restrict which users may reach which data.
The writable nodes can enable, disable and change the metrics used by routing, so unprotected writes can harm network operations. The RFC lists them: enable-receive, and on each interface the metric, both flags and exclude-te-metric, at the top level and under level-1 and level-2. The readable adjacency nodes may also be sensitive. For the implications of the feature itself, the RFC points to RFC 8500 and RFC 9130.
Changing these dials can steer traffic around a whole network, so only trusted people should be allowed to touch them, over a secure connection.
§6Examples
The appendix gives three examples of YANG instance data. The first, in XML, sets enable-receive to true for an IS-IS instance. The second, in XML, configures a metric of 65535 on interface eth0. The third, in JSON, sets a Level-1-only reverse metric of 65535 on eth0 together with exclude-te-metric set to true.
The examples are filled-in forms showing how to turn the feature on and how to set a number on one link.
§7References
[RFC8500]RFC 8500Shen, N., Amante, S., and M. Abrahamsson, "IS-IS Routing with Reverse Metric", RFC 8500, February 2019.February 2019[RFC9130]RFC 9130Litkowski, S., Ed., Yeung, D., Lindem, A., Zhang, J., and L. Lhotka, "YANG Data Model for the IS-IS Protocol", RFC 9130, October 2022.October 2022[RFC8349]RFC 8349Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for Routing Management (NMDA Version)", RFC 8349, March 2018.March 2018[RFC8342]RFC 8342Bjorklund, M., et al., "Network Management Datastore Architecture (NMDA)", RFC 8342, March 2018.March 2018[RFC8341]RFC 8341Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, March 2018.March 2018[RFC6241]RFC 6241Enns, R., Ed., et al., "Network Configuration Protocol (NETCONF)", RFC 6241, June 2011.June 2011[RFC8040]RFC 8040Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, January 2017.January 2017