rfc9492.original   rfc9492.txt 
LSR Working Group P. Psenak, Ed. Internet Engineering Task Force (IETF) P. Psenak, Ed.
Internet-Draft L. Ginsberg Request for Comments: 9492 L. Ginsberg
Obsoletes: 8920 (if approved) Cisco Systems Obsoletes: 8920 Cisco Systems
Intended status: Standards Track W. Henderickx Category: Standards Track W. Henderickx
Expires: 26 November 2023 Nokia ISSN: 2070-1721 Nokia
J. Tantsura J. Tantsura
Nvidia Nvidia
J. Drake J. Drake
Juniper Networks Juniper Networks
25 May 2023 October 2023
OSPF Application-Specific Link Attributes OSPF Application-Specific Link Attributes
draft-ietf-lsr-rfc8920bis-06
Abstract Abstract
Existing traffic-engineering-related link attribute advertisements Existing traffic-engineering-related link attribute advertisements
have been defined and are used in RSVP-TE deployments. Since the have been defined and are used in RSVP-TE deployments. Since the
original RSVP-TE use case was defined, additional applications (e.g., original RSVP-TE use case was defined, additional applications such
Segment Routing Policy and Loop-Free Alternates) that also make use as Segment Routing (SR) Policy and Loop-Free Alternates (LFAs) that
of the link attribute advertisements have been defined. In cases also make use of the link attribute advertisements have been defined.
where multiple applications wish to make use of these link In cases where multiple applications wish to make use of these link
attributes, the current advertisements do not support application- attributes, the current advertisements do not support application-
specific values for a given attribute, nor do they support indication specific values for a given attribute, nor do they support indication
of which applications are using the advertised value for a given of which applications are using the advertised value for a given
link. This document introduces new link attribute advertisements in link. This document introduces link attribute advertisements in
OSPFv2 and OSPFv3 that address both of these shortcomings. OSPFv2 and OSPFv3 that address both of these shortcomings.
This document obsoletes RFC 8920. This document obsoletes RFC 8920.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 26 November 2023. 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/rfc9492.
Copyright Notice Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language
2. Requirements Discussion . . . . . . . . . . . . . . . . . . . 4 2. Requirements Discussion
3. Existing Advertisement of Link Attributes . . . . . . . . . . 5 3. Existing Advertisement of Link Attributes
4. Advertisement of Link Attributes . . . . . . . . . . . . . . 5 4. Advertisement of Link Attributes
4.1. OSPFv2 Extended Link Opaque LSA and OSPFv3 4.1. OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA
E-Router-LSA . . . . . . . . . . . . . . . . . . . . . . 6 5. Advertisement of Application-Specific Values
5. Advertisement of Application-Specific Values . . . . . . . . 7 6. Reused TE Link Attributes
6. Reused TE Link Attributes . . . . . . . . . . . . . . . . . . 10 6.1. Shared Risk Link Group (SRLG)
6.1. Shared Risk Link Group (SRLG) . . . . . . . . . . . . . . 10 6.2. Extended Metrics
6.2. Extended Metrics . . . . . . . . . . . . . . . . . . . . 10 6.3. Administrative Group
6.3. Administrative Group . . . . . . . . . . . . . . . . . . 11 6.4. TE Metric
6.4. Traffic Engineering Metric . . . . . . . . . . . . . . . 12 7. Maximum Link Bandwidth
7. Maximum Link Bandwidth . . . . . . . . . . . . . . . . . . . 12 8. Considerations for Extended TE Metrics
8. Considerations for Extended TE Metrics . . . . . . . . . . . 12 9. Local Interface IPv6 Address Sub-TLV
9. Local Interface IPv6 Address Sub-TLV . . . . . . . . . . . . 13 10. Remote Interface IPv6 Address Sub-TLV
10. Remote Interface IPv6 Address Sub-TLV . . . . . . . . . . . . 13 11. Attribute Advertisements and Enablement
11. Attribute Advertisements and Enablement . . . . . . . . . . . 13 12. Deployment Considerations
12. Deployment Considerations . . . . . . . . . . . . . . . . . . 14 12.1. Use of Legacy RSVP-TE LSA Advertisements
12.1. Use of Legacy RSVP-TE LSA Advertisements . . . . . . . . 14 12.2. Use of Zero-Length Application Identifier Bit Masks
12.2. Use of Zero-Length Application Identifier Bit Masks . . 15
12.3. Interoperability, Backwards Compatibility, and Migration 12.3. Interoperability, Backwards Compatibility, and Migration
Concerns . . . . . . . . . . . . . . . . . . . . . . . . 15 Concerns
12.3.1. Multiple Applications: Common Attributes with 12.3.1. Multiple Applications: Common Attributes with RSVP-TE
RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . 16
12.3.2. Multiple Applications: Some Attributes Not Shared with 12.3.2. Multiple Applications: Some Attributes Not Shared with
RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . 16 RSVP-TE
12.3.3. Interoperability with Legacy Routers . . . . . . . . 16 12.3.3. Interoperability with Legacy Routers
12.3.4. Use of Application-Specific Advertisements for 12.3.4. Use of Application-Specific Advertisements for RSVP-TE
RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . 17 13. Security Considerations
13. Security Considerations . . . . . . . . . . . . . . . . . . . 17 14. IANA Considerations
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 14.1. OSPFv2
14.1. OSPFv2 . . . . . . . . . . . . . . . . . . . . . . . . . 18 14.2. OSPFv3
14.2. OSPFv3 . . . . . . . . . . . . . . . . . . . . . . . . . 19 15. Changes to RFC 8920
15. Changes to RFC 8920 . . . . . . . . . . . . . . . . . . . . . 19 16. References
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 16.1. Normative References
16.1. Normative References . . . . . . . . . . . . . . . . . . 20 16.2. Informative References
16.2. Informative References . . . . . . . . . . . . . . . . . 21 Acknowledgments
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 22 Contributors
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
NOTE: This document makes modest editorial changes to the content of
RFC 8920 which it obsoletes. A detailed description of the changes
is provided in Section 15. This note was added for the benefit of
IESG reviewers and SHOULD be removed by the RFC Editor prior to
publication.
Advertisement of link attributes by the OSPFv2 [RFC2328] and OSPFv3 Advertisement of link attributes by the OSPFv2 [RFC2328] and OSPFv3
[RFC5340] protocols in support of traffic engineering (TE) was [RFC5340] protocols in support of traffic engineering (TE) was
introduced by [RFC3630] and [RFC5329], respectively. It has been introduced by [RFC3630] and [RFC5329], respectively. It has been
extended by [RFC4203], [RFC7308], and [RFC7471]. Use of these extended by [RFC4203], [RFC7308], and [RFC7471]. Use of these
extensions has been associated with deployments supporting Traffic extensions has been associated with deployments supporting TE over
Engineering over Multiprotocol Label Switching (MPLS) in the presence Multiprotocol Label Switching (MPLS) in the presence of the Resource
of the Resource Reservation Protocol (RSVP), more succinctly referred Reservation Protocol (RSVP), more succinctly referred to as RSVP-TE
to as RSVP-TE [RFC3209]. [RFC3209].
For the purposes of this document, an application is a technology For the purposes of this document, an application is a technology
that makes use of link attribute advertisements, examples of which that makes use of link attribute advertisements, examples of which
are listed in Section 5. are listed in Section 5.
In recent years, new applications have been introduced that have use In recent years, new applications have been introduced that have use
cases for many of the link attributes historically used by RSVP-TE. cases for many of the link attributes historically used by RSVP-TE.
Such applications include Segment Routing (SR) Policy Such applications include SR Policy [RFC9256] and LFAs [RFC5286].
[SEGMENT-ROUTING] and Loop-Free Alternates (LFAs) [RFC5286]. This This has introduced ambiguity in that if a deployment includes a mix
has introduced ambiguity in that if a deployment includes a mix of of RSVP-TE support and SR Policy support, for example, it is not
RSVP-TE support and SR Policy support, for example, it is not
possible to unambiguously indicate which advertisements are to be possible to unambiguously indicate which advertisements are to be
used by RSVP-TE and which advertisements are to be used by SR Policy. used by RSVP-TE and which advertisements are to be used by SR Policy.
If the topologies are fully congruent, this may not be an issue, but If the topologies are fully congruent, this may not be an issue, but
any incongruence leads to ambiguity. any incongruence leads to ambiguity.
An example of where this ambiguity causes a problem is a network An example of where this ambiguity causes a problem is a network
where RSVP-TE is enabled only on a subset of its links. A link where RSVP-TE is enabled only on a subset of its links. A link
attribute is advertised for the purpose of another application (e.g., attribute is advertised for the purpose of another application (e.g.,
SR Policy) for a link that is not enabled for RSVP-TE. As soon as SR Policy) for a link that is not enabled for RSVP-TE. As soon as
the router that is an RSVP-TE head end sees the link attribute being the router that is an RSVP-TE head end sees the link attribute being
advertised for that link, it assumes RSVP-TE is enabled on that link, advertised for that link, it assumes RSVP-TE is enabled on that link,
even though it is not. If such an RSVP-TE head-end router tries to even though it is not. If such an RSVP-TE head-end router tries to
set up an RSVP-TE path via that link, it will result in the path set up an RSVP-TE path via that link, it will result in a setup
setup failure. failure for the path.
An additional issue arises in cases where both applications are An additional issue arises in cases where both applications are
supported on a link but the link attribute values associated with supported on a link but the link attribute values associated with
each application differ. Current advertisements do not support each application differ. Current advertisements do not support
advertising application-specific values for the same attribute on a advertising application-specific values for the same attribute on a
specific link. specific link.
This document defines extensions that address these issues. Also, as This document defines extensions that address these issues. Also, as
evolution of use cases for link attributes can be expected to evolution of use cases for link attributes can be expected to
continue in the years to come, this document defines a solution that continue in the years to come, this document defines a solution that
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As stated previously, evolution of use cases for link attributes can As stated previously, evolution of use cases for link attributes can
be expected to continue. Therefore, any discussion of existing use be expected to continue. Therefore, any discussion of existing use
cases is limited to requirements that are known at the time of this cases is limited to requirements that are known at the time of this
writing. However, in order to determine the functionality required writing. However, in order to determine the functionality required
beyond what already exists in OSPF, it is only necessary to discuss beyond what already exists in OSPF, it is only necessary to discuss
use cases that justify the key points identified in the introduction, use cases that justify the key points identified in the introduction,
which are: which are:
1. Support for indicating which applications are using the link 1. Support for indicating which applications are using the link
attribute advertisements on a link attribute advertisements on a link.
2. Support for advertising application-specific values for the same 2. Support for advertising application-specific values for the same
attribute on a link attribute on a link.
[RFC7855] discusses use cases and requirements for Segment Routing [RFC7855] discusses use cases and requirements for SR. Included
(SR). Included among these use cases is SR Policy, which is defined among these use cases is SR Policy, which is defined in [RFC9256].
in [SEGMENT-ROUTING]. If both RSVP-TE and SR Policy are deployed in If both RSVP-TE and SR Policy are deployed in a network, link
a network, link attribute advertisements can be used by one or both attribute advertisements can be used by one or both of these
of these applications. There is no requirement for the link applications. There is no requirement for the link attributes
attributes advertised on a given link used by SR Policy to be advertised on a given link used by SR Policy to be identical to the
identical to the link attributes advertised on that same link used by link attributes advertised on that same link used by RSVP-TE; thus,
RSVP-TE; thus, there is a clear requirement to indicate independently there is a clear requirement to indicate independently which link
which link attribute advertisements are to be used by each attribute advertisements are to be used by each application.
application.
As the number of applications that may wish to utilize link As the number of applications that may wish to utilize link
attributes may grow in the future, an additional requirement is that attributes may grow in the future, an additional requirement is that
the extensions defined allow the association of additional the extensions defined allow the association of additional
applications to link attributes without altering the format of the applications to link attributes without altering the format of the
advertisements or introducing new backwards-compatibility issues. advertisements or introducing backwards-compatibility issues.
Finally, there may still be many cases where a single attribute value Finally, there may still be many cases where a single attribute value
can be shared among multiple applications, so the solution must can be shared among multiple applications, so the solution must
minimize advertising duplicate link/attribute pairs whenever minimize advertising duplicate link/attribute pairs whenever
possible. possible.
3. Existing Advertisement of Link Attributes 3. Existing Advertisement of Link Attributes
There are existing advertisements used in support of RSVP-TE. These There are existing advertisements used in support of RSVP-TE. These
advertisements are carried in the OSPFv2 TE Opaque Link State advertisements are carried in the OSPFv2 TE Opaque Link State
skipping to change at page 7, line 8 skipping to change at line 262
The format of the link attribute TLVs that have been defined for The format of the link attribute TLVs that have been defined for
RSVP-TE applications will be kept unchanged even when they are used RSVP-TE applications will be kept unchanged even when they are used
for non-RSVP-TE applications. Unique codepoints are allocated for for non-RSVP-TE applications. Unique codepoints are allocated for
these link attribute TLVs from the "OSPFv2 Extended Link TLV Sub- these link attribute TLVs from the "OSPFv2 Extended Link TLV Sub-
TLVs" registry [RFC7684] and from the "OSPFv3 Extended-LSA Sub-TLVs" TLVs" registry [RFC7684] and from the "OSPFv3 Extended-LSA Sub-TLVs"
registry [RFC8362], as specified in Section 14. registry [RFC8362], as specified in Section 14.
5. Advertisement of Application-Specific Values 5. Advertisement of Application-Specific Values
To allow advertisement of the application-specific values of the link To allow advertisement of the application-specific values of the link
attribute, a new Application-Specific Link Attributes (ASLA) sub-TLV attribute, an Application-Specific Link Attributes (ASLA) sub-TLV is
is defined. The ASLA sub-TLV is a sub-TLV of the OSPFv2 Extended defined. The ASLA sub-TLV is a sub-TLV of the OSPFv2 Extended Link
Link TLV [RFC7684] and OSPFv3 Router-Link TLV [RFC8362]. TLV [RFC7684] and OSPFv3 Router-Link TLV [RFC8362].
In addition to advertising the link attributes for standardized In addition to advertising the link attributes for standardized
applications, link attributes can be advertised for the purpose of applications, link attributes can be advertised for the purpose of
applications that are not standardized. We call such an application applications that are not standardized. We call such an application
a "user-defined application" or "UDA". These applications are not a "user-defined application" or "UDA". These applications are not
subject to standardization and are outside of the scope of this subject to standardization and are outside of the scope of this
specification. specification.
The ASLA sub-TLV is an optional sub-TLV of the OSPFv2 Extended Link The ASLA sub-TLV is an optional sub-TLV of the OSPFv2 Extended Link
TLV and OSPFv3 Router-Link TLV. Multiple ASLA sub-TLVs can be TLV and OSPFv3 Router-Link TLV. Multiple ASLA sub-TLVs can be
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Extended Link TLV and OSPFv3 Router-Link TLV. It has the following Extended Link TLV and OSPFv3 Router-Link TLV. It has the following
format: format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SABM Length | UDABM Length | Reserved | | SABM Length | UDABM Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Standard Application Identifier Bit Mask(SABM) | | Standard Application Identifier Bit Mask (SABM) |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User-Defined Application Identifier Bit Mask(UDABM) | | User-Defined Application Identifier Bit Mask (UDABM) |
+- -+ +- -+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attribute sub-sub-TLVs | | Link Attribute sub-TLVs |
+- -+ +- -+
| ... | | ... |
where: where:
Type: 10 (OSPFv2), 11 (OSPFv3) Type: 10 (OSPFv2), 11 (OSPFv3)
Length: Variable Length: Variable
SABM Length: Standard Application Identifier Bit Mask Length in SABM Length:
octets. The value MUST be 0, 4, or 8. If the Standard Standard Application Identifier Bit Mask Length in octets. The
Application Identifier Bit Mask is not present, the SABM Length value MUST be 0, 4, or 8. If the Standard Application Identifier
MUST be set to 0. Bit Mask is not present, the SABM Length MUST be set to 0.
UDABM Length: User-Defined Application Identifier Bit Mask Length in UDABM Length:
octets. The value MUST be 0, 4, or 8. If the User-Defined User-Defined Application Identifier Bit Mask Length in octets.
Application Identifier Bit Mask is not present, the UDABM Length The value MUST be 0, 4, or 8. If the User-Defined Application
MUST be set to 0. Identifier Bit Mask is not present, the UDABM Length MUST be set
to 0.
Standard Application Identifier Bit Mask: Optional set of bits, Standard Application Identifier Bit Mask: Optional set of bits,
where each bit represents a single standard application. Bits are where each bit represents a single standard application. Bits are
defined in the "Link Attribute Applications" registry, which is defined in the "Link Attribute Application Identifiers" registry,
defined in [RFC8919]. Current assignments are repeated here for which is defined in [RFC9479]. Current assignments are repeated
informational purposes: here for informational purposes:
0 1 2 3 4 5 6 7 ... 0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+-+-+-+... +-+-+-+-+-+-+-+-+...
|R|S|F| ... |R|S|F| ...
+-+-+-+-+-+-+-+-+... +-+-+-+-+-+-+-+-+...
Bit 0 (R-bit): RSVP-TE. Bit 0 (R-bit): RSVP-TE.
Bit 1 (S-bit): Segment Routing Policy. (this is dataplane Bit 1 (S-bit): SR Policy (this is data plane independent).
independent).
Bit 2 (F-bit): Loop-Free Alternate (LFA). Includes all LFA Bit 2 (F-bit): Loop-Free Alternate (includes all LFA types).
types.
User-Defined Application Identifier Bit Mask: Optional set of bits, User-Defined Application Identifier Bit Mask:
where each bit represents a single user-defined application. Optional set of bits, where each bit represents a single user-
defined application.
If the SABM or UDABM Length is other than 0, 4, or 8, the ASLA sub- If the SABM or UDABM Length is other than 0, 4, or 8, the ASLA sub-
TLV MUST be ignored by the receiver. TLV MUST be ignored by the receiver.
Standard Application Identifier Bits are defined and sent starting Standard Application Identifier Bits are defined and sent starting
with bit 0. Undefined bits that are transmitted MUST be transmitted with bit 0. Undefined bits that are transmitted MUST be transmitted
as 0 and MUST be ignored on receipt. Bits that are not transmitted as 0 and MUST be ignored on receipt. Bits that are not transmitted
MUST be treated as if they are set to 0 on receipt. Bits that are MUST be treated as if they are set to 0 on receipt. Bits that are
not supported by an implementation MUST be ignored on receipt. not supported by an implementation MUST be ignored on receipt.
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Standard Application Identifier Bits and are not managed by IANA or Standard Application Identifier Bits and are not managed by IANA or
any other standards body. It is recommended that these bits be used any other standards body. It is recommended that these bits be used
starting with bit 0 so as to minimize the number of octets required starting with bit 0 so as to minimize the number of octets required
to advertise all UDAs. Undefined bits that are transmitted MUST be to advertise all UDAs. Undefined bits that are transmitted MUST be
transmitted as 0 and MUST be ignored on receipt. Bits that are not transmitted as 0 and MUST be ignored on receipt. Bits that are not
transmitted MUST be treated as if they are set to 0 on receipt. Bits transmitted MUST be treated as if they are set to 0 on receipt. Bits
that are not supported by an implementation MUST be ignored on that are not supported by an implementation MUST be ignored on
receipt. receipt.
If the link attribute advertisement is intended to be only used by a If the link attribute advertisement is intended to be only used by a
specific set of applications, corresponding bit masks MUST be specific set of applications, corresponding bit masks MUST be present
present, and application-specific bit(s) MUST be set for all and one or more application-specific bits MUST be set for all
applications that use the link attributes advertised in the ASLA sub- applications that use the link attributes advertised in the ASLA sub-
TLV. TLV.
Application Identifier Bit Masks apply to all link attributes that Application Identifier Bit Masks apply to all link attributes that
support application-specific values and are advertised in the ASLA support application-specific values and are advertised in the ASLA
sub-TLV. sub-TLV.
The advantage of not making the Application Identifier Bit Masks part The advantage of not making the Application Identifier Bit Masks part
of the attribute advertisement itself is that the format of any of the attribute advertisement itself is that the format of any
previously defined link attributes can be kept and reused when previously defined link attributes can be kept and reused when
advertising them in the ASLA sub-TLV. advertising them in the ASLA sub-TLV.
If the same attribute is advertised in more than one ASLA sub-TLVs If the same attribute is advertised in more than one ASLA sub-TLV
with the application listed in the Application Identifier Bit Masks, with the application listed in the Application Identifier Bit Masks,
the application SHOULD use the first instance of advertisement and the application SHOULD use the first instance of advertisement and
ignore any subsequent advertisements of that attribute. ignore any subsequent advertisements of that attribute.
Link attributes MAY be advertised associated with zero-length Link attributes MAY be advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and Application Identifier Bit Masks for both standard applications and
user-defined applications. Such link attribute advertisements MUST user-defined applications. Such link attribute advertisements MUST
be used by standard applications and/or user defined applications be used by standard applications and/or user-defined applications
when no link attribute advertisements with a non-zero-length when no link attribute advertisements with a non-zero-length
Application Identifier Bit Mask and a matching Application Identifier Application Identifier Bit Mask and a matching Application Identifier
Bit set are present. Otherwise, such link attribute advertisements Bit set are present. Otherwise, such link attribute advertisements
MUST NOT be used. MUST NOT be used.
This document defines the initial set of link attributes that MUST This document defines the initial set of link attributes that MUST
use the ASLA sub-TLV if advertised in the OSPFv2 Extended Link TLV or use the ASLA sub-TLV if advertised in the OSPFv2 Extended Link TLV or
in the OSPFv3 Router-Link TLV. Documents that define new link in the OSPFv3 Router-Link TLV. Documents that define new link
attributes MUST state whether the new attributes support application- attributes MUST state whether the new attributes support application-
specific values and, as such, are advertised in an ASLA sub-TLV. The specific values and, as such, are advertised in an ASLA sub-TLV. The
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This section defines the use case and indicates the codepoints This section defines the use case and indicates the codepoints
(Section 14) from the "OSPFv2 Extended Link TLV Sub-TLVs" registry (Section 14) from the "OSPFv2 Extended Link TLV Sub-TLVs" registry
and "OSPFv3 Extended-LSA Sub-TLVs" registry for some of the link and "OSPFv3 Extended-LSA Sub-TLVs" registry for some of the link
attributes that have been originally defined for RSVP-TE or GMPLS. attributes that have been originally defined for RSVP-TE or GMPLS.
6.1. Shared Risk Link Group (SRLG) 6.1. Shared Risk Link Group (SRLG)
The SRLG of a link can be used in OSPF-calculated IPFRR (IP Fast The SRLG of a link can be used in OSPF-calculated IPFRR (IP Fast
Reroute) [RFC5714] to compute a backup path that does not share any Reroute) [RFC5714] to compute a backup path that does not share any
SRLG group with the protected link. SRLG with the protected link.
To advertise the SRLG of the link in the OSPFv2 Extended Link TLV, To advertise the SRLG of the link in the OSPFv2 Extended Link TLV,
the same format for the sub-TLV defined in Section 1.3 of [RFC4203] the same format for the sub-TLV defined in Section 1.3 of [RFC4203]
is used with TLV type 11. Similarly, for OSPFv3 to advertise the is used with TLV type 11. Similarly, for OSPFv3 to advertise the
SRLG in the OSPFv3 Router-Link TLV, TLV type 12 is used. SRLG in the OSPFv3 Router-Link TLV, TLV type 12 is used.
6.2. Extended Metrics 6.2. Extended Metrics
[RFC3630] defines several link bandwidth types. [RFC7471] defines [RFC3630] defines several link bandwidth types. [RFC7471] defines
extended link metrics that are based on link bandwidth, delay, and extended link metrics that are based on link bandwidth, delay, and
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19: Administrative Group 19: Administrative Group
20: Extended Administrative Group 20: Extended Administrative Group
To advertise the Administrative Group and Extended Administrative To advertise the Administrative Group and Extended Administrative
Group in the OSPFv3 Router-Link TLV, the same format for the sub-TLVs Group in the OSPFv3 Router-Link TLV, the same format for the sub-TLVs
defined in [RFC3630] and [RFC7308] is used with the following TLV defined in [RFC3630] and [RFC7308] is used with the following TLV
types: types:
20: Administrative Group 20: Administrative Group
21: Extended Administrative Group 21: Extended Administrative Group
6.4. Traffic Engineering Metric 6.4. TE Metric
[RFC3630] defines the Traffic Engineering Metric. [RFC3630] defines the TE Metric.
To advertise the Traffic Engineering Metric in the OSPFv2 Extended To advertise the TE Metric in the OSPFv2 Extended Link TLV, the same
Link TLV, the same format for the sub-TLV defined in Section 2.5.5 of format for the sub-TLV defined in Section 2.5.5 of [RFC3630] is used
[RFC3630] is used with TLV type 22. Similarly, for OSPFv3 to with TLV type 22. Similarly, for OSPFv3 to advertise the TE Metric
advertise the Traffic Engineering Metric in the OSPFv3 Router-Link in the OSPFv3 Router-Link TLV, TLV type 22 is used.
TLV, TLV type 22 is used.
7. Maximum Link Bandwidth 7. Maximum Link Bandwidth
Maximum link bandwidth is an application-independent attribute of the Maximum link bandwidth is an application-independent attribute of the
link that is defined in [RFC3630]. Because it is an application- link that is defined in [RFC3630]. Because it is an application-
independent attribute, it MUST NOT be advertised in the ASLA sub-TLV. independent attribute, it MUST NOT be advertised in the ASLA sub-TLV.
Instead, it MAY be advertised as a sub-TLV of the Extended Link TLV Instead, it MAY be advertised as a sub-TLV of the Extended Link TLV
in the Extended Link Opaque LSA in OSPFv2 [RFC7684] or as a sub-TLV in the Extended Link Opaque LSA in OSPFv2 [RFC7684] or as a sub-TLV
of the Router-Link TLV in the E-Router-LSA Router-Link TLV in OSPFv3 of the Router-Link TLV in the E-Router-LSA Router-Link TLV in OSPFv3
[RFC8362]. [RFC8362].
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In the case of LFA, the advertisement of application-specific link In the case of LFA, the advertisement of application-specific link
attributes does not indicate enablement of LFA on that link. attributes does not indicate enablement of LFA on that link.
Enablement is controlled by local configuration. Enablement is controlled by local configuration.
In the future, if additional standard applications are defined to use In the future, if additional standard applications are defined to use
this mechanism, the specification defining this use MUST define the this mechanism, the specification defining this use MUST define the
relationship between application-specific link attribute relationship between application-specific link attribute
advertisements and enablement for that application. advertisements and enablement for that application.
This document allows the advertisement of application-specific link This document allows the advertisement of application-specific link
attributes with no application identifiers, i.e., both the Standard attributes with no application identifiers, i.e., both the SABM and
Application Identifier Bit Mask and the User-Defined Application the UDABM are not present (see Section 5). This supports the use of
Identifier Bit Mask are not present (see Section 5). This supports the link attribute by any application. In the presence of an
the use of the link attribute by any application. In the presence of application where the advertisement of link attributes is used to
an application where the advertisement of link attributes is used to
infer the enablement of an application on that link (e.g., RSVP-TE), infer the enablement of an application on that link (e.g., RSVP-TE),
the absence of the application identifier leaves ambiguous whether the absence of the application identifier leaves ambiguous whether
that application is enabled on such a link. This needs to be that application is enabled on such a link. This needs to be
considered when making use of the "any application" encoding. considered when making use of the "any application" encoding.
12. Deployment Considerations 12. Deployment Considerations
12.1. Use of Legacy RSVP-TE LSA Advertisements 12.1. Use of Legacy RSVP-TE LSA Advertisements
Bit identifiers for standard applications are defined in Section 5. Bit identifiers for standard applications are defined in Section 5.
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advertisements defined in this document MUST NOT make use of RSVP-TE advertisements defined in this document MUST NOT make use of RSVP-TE
LSA advertisements. This simplifies deployment of new applications LSA advertisements. This simplifies deployment of new applications
by eliminating the need to support multiple ways to advertise by eliminating the need to support multiple ways to advertise
attributes for the new applications. attributes for the new applications.
12.2. Use of Zero-Length Application Identifier Bit Masks 12.2. Use of Zero-Length Application Identifier Bit Masks
Link attribute advertisements associated with zero-length Application Link attribute advertisements associated with zero-length Application
Identifier Bit Masks for both standard applications and user-defined Identifier Bit Masks for both standard applications and user-defined
applications are usable by any application, subject to the applications are usable by any application, subject to the
restrictions specified in Section 4.2. If support for a new restrictions specified in Section 5. If support for a new
application is introduced on any node in a network in the presence of application is introduced on any node in a network in the presence of
such advertisements, the new application will use these such advertisements, the new application will use these
advertisements, when the aforementioned restrictions are met. If advertisements when the aforementioned restrictions are met. If this
this is not what is intended, then existing link attribute is not what is intended, then existing link attribute advertisements
advertisements MUST be readvertised with an explicit set of MUST be readvertised with an explicit set of applications specified
applications specified before a new application is introduced. before a new application is introduced.
12.3. Interoperability, Backwards Compatibility, and Migration Concerns 12.3. Interoperability, Backwards Compatibility, and Migration Concerns
Existing deployments of RSVP-TE, SR Policy, and/or LFA utilize the Existing deployments of RSVP-TE, SR Policy, and/or LFA utilize the
legacy advertisements listed in Section 3. Routers that do not legacy advertisements listed in Section 3. Routers that do not
support the extensions defined in this document will only process support the extensions defined in this document will only process
legacy advertisements and are likely to infer that RSVP-TE is enabled legacy advertisements and are likely to infer that RSVP-TE is enabled
on the links for which legacy advertisements exist. It is expected on the links for which legacy advertisements exist. It is expected
that deployments using the legacy advertisements will persist for a that deployments using the legacy advertisements will persist for a
significant period of time. Therefore, deployments using the significant period of time. Therefore, deployments using the
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Implementations must ensure that if any of the TLVs and sub-TLVs Implementations must ensure that if any of the TLVs and sub-TLVs
defined in this document are malformed, they are detected and do not defined in this document are malformed, they are detected and do not
facilitate a vulnerability for attackers to crash or otherwise facilitate a vulnerability for attackers to crash or otherwise
compromise the OSPF router or routing process. Reception of a compromise the OSPF router or routing process. Reception of a
malformed TLV or sub-TLV SHOULD be counted and/or logged for further malformed TLV or sub-TLV SHOULD be counted and/or logged for further
analysis. Logging of malformed TLVs and sub-TLVs SHOULD be rate- analysis. Logging of malformed TLVs and sub-TLVs SHOULD be rate-
limited to prevent a denial-of-service (DoS) attack (distributed or limited to prevent a denial-of-service (DoS) attack (distributed or
otherwise) from overloading the OSPF control plane. otherwise) from overloading the OSPF control plane.
This document defines a new way to advertise link attributes. This document defines an improved way to advertise link attributes.
Tampering with the information defined in this document may have an Tampering with the information defined in this document may have an
effect on applications using it, including impacting traffic effect on applications using it, including impacting TE, which uses
engineering, which uses various link attributes for its path various link attributes for its path computation. This is similar in
computation. This is similar in nature to the impacts associated nature to the impacts associated with, for example, [RFC3630]. As
with, for example, [RFC3630]. As the advertisements defined in this the advertisements defined in this document limit the scope to
document limit the scope to specific applications, the impact of specific applications, the impact of tampering is similarly limited
tampering is similarly limited in scope. in scope.
14. IANA Considerations 14. IANA Considerations
This specification updates two existing registries: This specification updates two existing registries:
* the "OSPFv2 Extended Link TLV Sub-TLVs" registry * the "OSPFv2 Extended Link TLV Sub-TLVs" registry
* the "OSPFv3 Extended-LSA Sub-TLVs" registry * the "OSPFv3 Extended-LSA Sub-TLVs" registry
The new values defined in this document have been allocated using the The values defined in this document have been allocated using the
IETF Review procedure as described in [RFC8126]. IETF Review procedure as described in [RFC8126].
14.1. OSPFv2 14.1. OSPFv2
The "OSPFv2 Extended Link TLV Sub-TLVs" registry [RFC7684] defines The "OSPFv2 Extended Link TLV Sub-TLVs" registry [RFC7684] defines
sub-TLVs at any level of nesting for OSPFv2 Extended Link TLVs. IANA sub-TLVs at any level of nesting for OSPFv2 Extended Link TLVs. IANA
has assigned the following sub-TLV types from the "OSPFv2 Extended has assigned the following sub-TLV types in the "OSPFv2 Extended Link
Link TLV Sub-TLVs" registry: TLV Sub-TLVs" registry:
10: Application-Specific Link Attributes 10: Application-Specific Link Attributes
11: Shared Risk Link Group 11: Shared Risk Link Group
12: Unidirectional Link Delay 12: Unidirectional Link Delay
13: Min/Max Unidirectional Link Delay 13: Min/Max Unidirectional Link Delay
14: Unidirectional Delay Variation 14: Unidirectional Delay Variation
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20: Extended Administrative Group 20: Extended Administrative Group
22: TE Metric 22: TE Metric
23: Maximum link bandwidth 23: Maximum link bandwidth
14.2. OSPFv3 14.2. OSPFv3
The "OSPFv3 Extended-LSA Sub-TLVs" registry [RFC8362] defines sub- The "OSPFv3 Extended-LSA Sub-TLVs" registry [RFC8362] defines sub-
TLVs at any level of nesting for OSPFv3 Extended LSAs. IANA has TLVs at any level of nesting for OSPFv3 Extended LSAs. IANA has
assigned the following sub-TLV types from the "OSPFv3 Extended-LSA assigned the following sub-TLV types in the "OSPFv3 Extended-LSA Sub-
Sub-TLVs" registry: TLVs" registry:
11: Application-Specific Link Attributes 11: Application-Specific Link Attributes
12: Shared Risk Link Group 12: Shared Risk Link Group
13: Unidirectional Link Delay 13: Unidirectional Link Delay
14: Min/Max Unidirectional Link Delay 14: Min/Max Unidirectional Link Delay
15: Unidirectional Delay Variation 15: Unidirectional Delay Variation
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23: Maximum link bandwidth 23: Maximum link bandwidth
24: Local Interface IPv6 Address 24: Local Interface IPv6 Address
25: Remote Interface IPv6 Address 25: Remote Interface IPv6 Address
15. Changes to RFC 8920 15. Changes to RFC 8920
Discussion within the LSR WG indicated that there was confusion Discussion within the LSR WG indicated that there was confusion
regarding the use of ASLA advertisements that had a zero length SABM/ regarding the use of ASLA advertisements that had a zero-length SABM/
UDABM. The discussion can be seen by searching the LSR WG mailing UDABM. The discussion can be seen by searching the LSR WG mailing
list archives for the thread "Proposed Errata for RFCs 8919/8920" list archives for the thread "Proposed Errata for RFCs 8919/8920"
starting on 15 June 2021. starting on 15 June 2021.
Changes to Section 5 have been introduced to clarify normative Changes to Section 5 have been introduced to clarify normative
behavior in the presence of such advertisements. RFC 8920 defines behavior in the presence of such advertisements. [RFC8920] defines
advertising link attributes with zero length Standard Application Bit advertising link attributes with zero-length SABM and zero-length
Mask (SABM) and zero length User Defined ApplicationBit Mask (UDABM) UDABM as a means of advertising link attributes that can be used by
as a means of advertising link attributes that can be used by any any application. However, the text uses the word "permitted",
application. However, the text uses the word "permitted", suggesting suggesting that the use of such advertisements is "optional". Such
that the use of such advertisements is "optional". Such an an interpretation could lead to interoperability issues and is not
interpretation could lead to interoperability issues and is not what what was intended.
was intended.
The replacement text makes explicit the specific conditions when such The replacement text makes explicit the specific conditions when such
advertisements MUST be used and the specific conditions under which advertisements MUST be used and the specific conditions under which
they MUST NOT be used. they MUST NOT be used.
A new subsection discussing the use of zero-length Application A subsection discussing the use of zero-length Application Identifier
Identifier Bit Masks has been added for greater consistency with Bit Masks has been added for greater consistency with [RFC9479]. See
[RFC8919]. See Section 12.2. Section 12.2.
16. References 16. References
16.1. Normative References 16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 21, line 29 skipping to change at line 950
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA) F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>. 2018, <https://www.rfc-editor.org/info/rfc8362>.
[RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and [RFC9479] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS Application-Specific Link Attributes", J. Drake, "IS-IS Application-Specific Link Attributes",
RFC 8919, DOI 10.17487/RFC8919, October 2020, RFC 9479, DOI 10.17487/RFC9479, October 2023,
<https://www.rfc-editor.org/info/rfc8919>. <https://www.rfc-editor.org/info/rfc9479>.
16.2. Informative References 16.2. Informative References
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>. <https://www.rfc-editor.org/info/rfc3209>.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
skipping to change at page 22, line 35 skipping to change at line 1001
Litkowski, S., Horneffer, M., and R. Shakir, "Source Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <https://www.rfc-editor.org/info/rfc7855>. 2016, <https://www.rfc-editor.org/info/rfc7855>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[SEGMENT-ROUTING] [RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and J., and J. Drake, "OSPF Application-Specific Link
P. Mattes, "Segment Routing Policy Architecture", STD 54, Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020,
RFC 9256, DOI 10.17487/RFC9256, 24 July 2022, <https://www.rfc-editor.org/info/rfc8920>.
<https://www.rfc-editor.org/rfc/rfc9256>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
Acknowledgments Acknowledgments
RFC 8920 included the following acknowledgments: The following acknowledgments are included in [RFC8920]:
Thanks to Chris Bowers for his review and comments. Thanks to Chris Bowers for his review and comments.
Thanks to Alvaro Retana for his detailed review and comments. Thanks to Alvaro Retana for his detailed review and comments.
For the new version, the authors would like to thank Bruno Decraene. For this document, the authors would like to thank Bruno Decraene.
Contributors Contributors
The following people contributed to the content of this document and The following people contributed to the content of this document and
should be considered as coauthors: should be considered as coauthors:
Acee Lindem Acee Lindem
Cisco Systems LabN Consulting, L.L.C.
United States of America United States of America
Email: acee@cisco.com Email: acee.ietf@gmail.com
Ketan Talaulikar Ketan Talaulikar
Arrcus, Inc. Cisco Systems
India India
Email: ketant.ietf@gmail.com Email: ketant.ietf@gmail.com
Hannes Gredler Hannes Gredler
RtBrick Inc. RtBrick Inc.
Email: hannes@rtbrick.com Email: hannes@rtbrick.com
Authors' Addresses Authors' Addresses
Peter Psenak (editor) Peter Psenak (editor)
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