Inter-Domain Routing K. Talaulikar
Internet-Draft P. Psenak
Intended status: Standards Track Cisco Systems
Expires: January 26, 2021 J. Tantsura
Apstra
July 25, 2020
Application-Specific Attributes Advertisement with BGP Link-State
draft-ietf-idr-bgp-ls-app-specific-attr-03
Abstract
Various link attributes have been defined in link-state routing
protocols like OSPF and IS-IS in the context of the MPLS Traffic
Engineering (TE) and GMPLS. BGP Link-State (BGP-LS) extensions have
been defined to distribute these attributes along with other topology
information from these link-state routing protocols. Many of these
link attributes can be used for applications other than MPLS-TE or
GMPLS.
Extensions to link-state routing protocols have been defined for such
link attributes that enable distribution of their application-
specific values. This document defines extensions to BGP-LS address-
family to enable advertisement of these application-specific
attributes as a part of the topology information from the network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 26, 2021.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Application Specific Link Attributes TLV . . . . . . . . . . 3
3. Application Specific Link Attributes . . . . . . . . . . . . 5
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 9
6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Manageability Considerations . . . . . . . . . . . . . . . . 10
8.1. Operational Considerations . . . . . . . . . . . . . . . 10
8.2. Management Considerations . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Various link attributes have been defined in link-state routing
protocols (viz., IS-IS [RFC1195], OSPFv2 [RFC2328] and OSPFv3
[RFC5340] ) in the context of the MPLS traffic engineering and GMPLS.
All these attributes are distributed by these protocols using TLVs
that were originally defined for traditional MPLS Traffic Engineering
(i.e., using RSVP-TE [RFC3209]) or GMPLS [RFC4202] applications.
In recent years new applications have been introduced that have use
cases for many of the link attributes historically used by RSVP-TE
and GMPLS. Such applications include Segment Routing (SR) [RFC8402]
and Loop Free Alternates (LFA) [RFC5286]. This has introduced
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ambiguity in that if a deployment includes a mix of RSVP-TE support
and SR support (for example) it is not possible to unambiguously
indicate which advertisements are to be used by RSVP-TE and which
advertisements are to be used by SR. If the topologies are fully
congruent this may not be an issue, but any incongruence leads to
ambiguity. An additional issue arises in cases where both
applications are supported on a link but the link attribute values
associated with each application differ. Current advertisements do
not support advertising application-specific values for the same
attribute on a specific link. IGP Flexible Algorithm
[I-D.ietf-lsr-flex-algo] is one such application use case that MAY
use application-specific link attributes.
[I-D.ietf-ospf-te-link-attr-reuse] and [I-D.ietf-isis-te-app] define
extensions for OSPF and IS-IS respectively that address these issues.
Also, as evolution of use cases for link attributes can be expected
to continue in the years to come, these documents define a solution
that is easily extensible to the introduction of new applications and
new use cases.
BGP Link-State extensions [RFC7752] have been specified to enable
distribution of the link-state topology information from the IGPs to
an application like a controller or Path Computation Engine (PCE) via
BGP. The controller/PCE gets the end-to-end topology information
across IGP domains so it can perform path computations for use cases
like end-to-end traffic engineering (TE) using RSVP-TE or SR-based
mechanisms. A similar challenge to what was described above is hence
also faced by such centralized computation entities.
There is thus a need for BGP-LS extensions to also report link
attributes on a per-application basis on the same lines as introduced
in the link-state routing protocols. This document defines these
BGP-LS extensions and also covers the backward compatibility issues
related to existing BGP-LS deployments.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Application Specific Link Attributes TLV
The BGP-LS [RFC7752] specifies the Link NLRI for advertisement of
links and their attributes using the BGP-LS Attribute. The
Application-Specific Link Attributes (ASLA) TLV is a new optional
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top-level BGP-LS Attribute TLV that is introduced for Link NLRIs. It
is defined such that it may act as a container for certain existing
and future link attributes that require application-specific
definition.
The format of this TLV is as follows and is similar to the
corresponding ASLA sub-TLVs defined for OSPF and IS-IS in
[I-D.ietf-ospf-te-link-attr-reuse] and [I-D.ietf-isis-te-app]
respectively.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SABML | UDABML | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Standard Application Identifier Bit Mask (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User-Defined Application Identifier Bit Mask (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attribute sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Application-Specific Link Attributes TLV
where:
o Type: 1122
o Length: variable.
o SABML : Standard Application Identifier Bit Mask Length in octets.
The values MUST be 0, 4, or 8. If the Standard Application
Identifier Bit Mask is not present, the SABML MUST be set to 0.
o UDABML : User-Defined Application Identifier Bit Mask Length in
octets. The values MUST be 0, 4, or 8. If the User-Defined
Application Identifier Bit Mask is not present, the UDABML MUST be
set to 0.
o Standard Application Identifier Bit Mask : of size 0, 4, or 8
octets as indicated by the SABML. Optional set of bits, where
each bit represents a single standard application. The bits are
defined in the IANA "IGP Parameters" registries under the "Link
Attribute Applications" registry [I-D.ietf-isis-te-app].
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o User-Defined Application Identifier Bit Mask : of size 0, 4, or 8
octets as indicated by the UDABML. Optional set of bits, where
each bit represents a single user-defined application. The bits
are not managed or assigned by IANA or any other standards body
and definition is left to the implementation.
o sub-TLVs : BGP-LS Attribute TLVs corresponding to the Link NLRI
that are application-specific (as specified in Section 3) are
included as sub-TLVs of the ASLA TLV.
An ASLA TLV with both the SABML and UDABML set to 0 (i.e. without any
application identifier bit masks) indicates that the link attribute
sub-TLVs that it encloses are applicable for all applications.
The ASLA TLV and its sub-TLVs can only be added to the BGP-LS
Attribute associated with the Link NLRI of the node that originates
the underlying IGP link attribute TLVs/sub-TLVs. The procedures for
originating link attributes in the ASLA TLV from underlying IGPs are
specified in Section 4.
When the node is not running any of the IGPs but running a protocol
like BGP, then the link attributes for the node's local links MAY be
originated as part of the BGP-LS Attribute using the ASLA TLV and its
sub-TLVs within the Link NLRI corresponding to the local node.
3. Application Specific Link Attributes
Several BGP-LS Attribute TLVs corresponding to the Link NLRI are
defined in BGP-LS and more may be added in the future. The following
types of link attributes are required to be considered as application
specific.
o those that have different values for different applications (e.g.,
a different TE metric value used for RSVP-TE than for SR TE)
o those that are applicable to multiple applications but need to be
used only by specific application (e.g., certain SRLG values are
configured on a node for LFA but the same do not need to be used
for RSVP-TE)
The following table lists the currently defined BGP-LS Attributes
TLVs corresponding to Link NLRI that have application-specific
semantics. They were originally defined with semantics for RSVP-TE
and GMPLS applications.
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+----------+----------------------+---------------------------------+
| TLV Code | Description | Reference Document |
| Point | | |
+----------+----------------------+---------------------------------+
| 1088 | Administrative group | [RFC7752] |
| | (color) | |
| 1092 | TE Metric | [RFC7752] |
| 1096 | SRLG | [RFC7752] |
| 1114 | Unidirectional link | [RFC8571] |
| | delay | |
| 1115 | Min/Max | [RFC8571] |
| | Unidirectional link | |
| | delay | |
| 1116 | Unidirectional link | [RFC8571] |
| | delay variation | |
| 1117 | Unidirectional | [RFC8571] |
| | packet loss | |
| 1118 | Unidirectional | [RFC8571] |
| | residual bandwidth | |
| 1119 | Unidirectional | [RFC8571] |
| | available bandwidth | |
| 1120 | Unidirectional | [RFC8571] |
| | bandwidth | |
| | utilization | |
| 1173 | Extended | [I-D.ietf-idr-eag-distribution] |
| | Administrative group | |
| | (color) | |
+----------+----------------------+---------------------------------+
Table 1: BGP-LS Attribute TLVs also used as sub-TLVs of ASLA TLV
All the BGP-LS Attribute TLVs defined in the table above are
RECOMMENDED to continue to be advertised at the top-level in the BGP-
LS Attribute for carrying attributes specific to RSVP-TE without the
use of the ASLA TLV.
When a new link attribute is introduced, it may be thought of as
being specific to only a single application. However, subsequently,
it may be also shared by other applications and/or require
application-specific values. In such cases, it is RECOMMENDED to err
on the side of caution and define such attributes as application-
specific to ensure flexibility in the future.
BGP-LS Attribute TLVs corresponding to Link NLRI that are defined in
the future MUST specify if they are application-specific and hence
are REQUIRED to be encoded within an ASLA TLV.
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Only application-specific link attributes need to be advertised
within the ASLA TLV. Link attributes that do not have application-
specific semantics SHOULD NOT be advertised within the ASLA TLV.
Receivers SHOULD ignore any non-application-specific attribute sub-
TLVs within the ASLA TLV.
4. Procedures
The procedures described in this section apply to networks where all
BGP-LS originators and consumers support this specification. The
backward compatibility aspects and operations in deployments where
there are some BGP-LS originators or consumers that do not support
this specification are described further in Section 6.
The BGP-LS originator learns of the association of an application-
specific attribute to one or more applications from either the
underlying IGP protocol LSA/LSPs from which it is advertising the
topology information or from the local node configuration when
advertising attributes for the local node only.
The association of an application-specific link attribute with a
specific application context when advertising attributes for the
local node only (e.g., when running BGP as the only routing protocol)
is an implementation specific matter and outside the scope of this
document.
[I-D.ietf-ospf-te-link-attr-reuse] and [I-D.ietf-isis-te-app] specify
the mechanisms for advertising application-specific link attributes
in OSPFv2/v3 and IS-IS respectively. These IGP specifications also
describe the backward compatibility aspects and the existing RSVP-TE/
GMPLS specific TLV encoding mechanisms in the respective protocols.
A BGP-LS originator node that is advertising link-state information
from the underlying IGP determines the protocol encoding of
application-specific link attributes based on the following rules:
1. Application-specific link attributes received from an IGP node
using existing RSVP-TE/GMPLS encodings MUST be encoded using the
respective BGP-LS top-level TLVs listed in Table 1.
2. Application-specific link attributes received from an IGP node
using ASLA sub-TLV MUST be encoded in the BGP-LS ASLA TLV as sub-
TLVs.
3. In case of IS-IS, the following specific procedures are to be
followed:
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* When application-specific link attributes are received from a
node with the L bit set in the ASLA sub-TLV AND application
bits other than RSVP-TE are set in the application bit masks
then the application-specific link attributes advertised in
the corresponding legacy IS-IS TLVs/sub-TLVs MUST be encoded
within the BGP-LS ASLA TLV as sub-TLVs with the application
bits, other than the RSVP-TE bit, copied from the IS-IS ASLA
sub-TLV. The link attributes advertised in the legacy IS-IS
TLVs/sub-TLVs are also advertised in BGP-LS top-level TLVs
listed in Table 1. Note that this is true regardless of
whether the RSVP-TE bit was set in the IS-IS ASLA TLV/sub-TLV.
* When the ASLA sub-TLV has the RSVP-TE application bit set,
then the link attributes for the corresponding ASLA sub-TLV
MUST be encoded using the respective BGP-LS top-level TLVs
listed in Table 1.
* [I-D.ietf-isis-te-app] allows the advertisement of the Maximum
Link Bandwidth within an ASLA sub-TLV even though it is not an
application-specific attribute. However, when originating the
Maximum Link Bandwidth into BGP-LS, the attribute MUST be
encoded only in the top-level BGP-LS Maximum Link Bandwidth
TLV (1089) and not within the BGP-LS ASLA TLV.
* [I-D.ietf-isis-te-app] also allows the advertisement of the
Maximum Reservable Link Bandwidth and the Unreserved Bandwidth
within an ASLA sub-TLV even though these attributes are
specific to RSVP-TE application. However, when originating
the Maximum Reservable Link Bandwidth and Unreserved Bandwidth
into BGP-LS, these attributes MUST be encoded only in the BGP-
LS top-level Maximum Reservable Link Bandwidth TLV (1090) and
Unreserved Bandwidth TLV (1091) respectively and not within
the BGP-LS ASLA TLV.
These rules ensure that a BGP-LS originator performs the
advertisement for all application-specific link attributes from the
IGP nodes that support or do not support the ASLA extension.
Furthermore, it also ensures that the top-level BGP-LS TLVs defined
for RSVP-TE and GMPLS applications continue to be used for
advertisement of their application-specific attributes.
A BGP-LS consumer node would normally receive all the application-
specific link attributes corresponding to RSVP-TE and GMPLS
applications as existing top-level BGP-LS TLVs while for other
applications they are encoded in ASLA TLV(s) with appropriate
applicable bit mask setting. A BGP-LS consumer that implements this
specification SHOULD prefer the application-specific attribute value
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received via sub-TLVs within the ASLA TLV over the value received via
the top level TLVs.
5. Deployment Considerations
SR-TE and LFA applications have been deployed in some networks using
the IGP link attributes defined originally for RSVP-TE as discussed
in [I-D.ietf-ospf-te-link-attr-reuse] and [I-D.ietf-isis-te-app].
The corresponding BGP-LS top-level link attribute TLVs originally
defined for RSVP-TE have also been similarly used for SR-TE and LFA
applications by BGP-LS consumers. Such usage MAY continue without
requiring the support of the application-specific link attribute
encodings described in this document as long as the following
conditions are met:
o The application is SRTE or LFA and RSVP-TE is not deployed
anywhere in the network
o The application is SRTE or LFA, RSVP-TE is deployed in the
network, and both the set of links on which SRTE and/or LFA
advertisements are required and the attribute values used by SRTE
and/or LFA on all such links is fully congruent with the links and
attribute values used by RSVP-TE
6. Backward Compatibility
The backward compatibility aspects for BGP-LS are associated with the
originators (i.e., nodes) and consumers (e.g., PCE, controllers,
applications, etc.) of the topology information. BGP-LS
implementations have been originating link attributes and consuming
them without any application-specific scoping prior to the extensions
specified in this document.
IGP backwards compatibility aspects associated with application-
specific link attributes for RSVP-TE, SRTE and LFA applications are
discussed in the Backward Compatibility sections of
[I-D.ietf-ospf-te-link-attr-reuse] and [I-D.ietf-isis-te-app]. While
the backwards compatibility aspects ensure compatibility of IGP
advertisements, they also serve to ensure the backward compatibility
of the BGP-LS advertisements used by BGP-LS consumers. In
deployments where the BGP-LS originators or consumers do not support
the extensions specified in this document, the IGPs need to continue
to advertise link attributes intended for use by SRTE and LFA
applications using the RSVP-TE/GMPLS encodings. This allows BGP-LS
advertisements to be consistent with the behavior prior to the
extensions defined in this document
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It is RECOMMENDED that nodes that support this specification are
selected as originators of BGP-LS information when advertising the
link-state information from the IGPs.
7. IANA Considerations
This document requests assignment of code-points from the registry
"BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and
Attribute TLVs" based on table below which reflects the values
assigned via the early allocation process. The column "IS-IS TLV/
Sub-TLV" defined in the registry does not require any value and
should be left empty.
+------------+------------------------------------------+----------+
| Code Point | Description | Length |
+------------+------------------------------------------+----------+
| 1122 | Application-Specific Link Attributes TLV | variable |
+------------+------------------------------------------+----------+
8. Manageability Considerations
This section is structured as recommended in [RFC5706].
The new protocol extensions introduced in this document augment the
existing IGP topology information defined in [RFC7752]. Procedures
and protocol extensions defined in this document do not affect the
BGP protocol operations and management other than as discussed in the
Manageability Considerations section of [RFC7752]. Specifically, the
malformed NLRIs attribute tests in the Fault Management section of
[RFC7752] now encompass the BGP-LS TLVs defined in this document.
8.1. Operational Considerations
No additional operation considerations are defined in this document.
8.2. Management Considerations
No additional management considerations are defined in this document.
9. Security Considerations
The new protocol extensions introduced in this document augment the
existing IGP topology information defined in [RFC7752]. Procedures
and protocol extensions defined in this document do not affect the
BGP security model other than as discussed in the Security
Considerations section of [RFC7752].
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10. Acknowledgements
The authors would like to thank Les Ginsberg, Baalajee S, Amalesh
Maity, and Acee Lindem for their review and feedback on this
document.
11. References
11.1. Normative References
[I-D.ietf-isis-te-app]
Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS Application-Specific Link Attributes",
draft-ietf-isis-te-app-19 (work in progress), June 2020.
[I-D.ietf-ospf-te-link-attr-reuse]
Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J.,
and J. Drake, "OSPF Application-Specific Link Attributes",
draft-ietf-ospf-te-link-attr-reuse-16 (work in progress),
June 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[I-D.ietf-idr-eag-distribution]
Wang, Z., WU, Q., Tantsura, J., and K. Talaulikar,
"Distribution of Traffic Engineering Extended Admin Groups
using BGP-LS", draft-ietf-idr-eag-distribution-12 (work in
progress), May 2020.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-08 (work in progress), July 2020.
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[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
<https://www.rfc-editor.org/info/rfc4202>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/info/rfc5286>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC5706, November 2009,
<https://www.rfc-editor.org/info/rfc5706>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
IGP Traffic Engineering Performance Metric Extensions",
RFC 8571, DOI 10.17487/RFC8571, March 2019,
<https://www.rfc-editor.org/info/rfc8571>.
Authors' Addresses
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Ketan Talaulikar
Cisco Systems
India
Email: ketant@cisco.com
Peter Psenak
Cisco Systems
Slovakia
Email: ppsenak@cisco.com
Jeff Tantsura
Apstra
Email: jefftant.ietf@gmail.com
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