Internet DRAFT - draft-ketant-idr-bgp-ls-app-specific-attr
draft-ketant-idr-bgp-ls-app-specific-attr
Inter-Domain Routing K. Talaulikar
Internet-Draft P. Psenak
Intended status: Standards Track Cisco Systems
Expires: August 26, 2019 J. Tantsura
Apstra
February 22, 2019
Application Specific Attributes Advertisement with BGP Link-State
draft-ketant-idr-bgp-ls-app-specific-attr-01
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 which 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.
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.
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
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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 August 26, 2019.
Copyright Notice
Copyright (c) 2019 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Application Specific Link Attributes TLV . . . . . . . . . . 3
3. Application Specific Link Attributes . . . . . . . . . . . . 5
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Backward Compatibility . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Manageability Considerations . . . . . . . . . . . . . . . . 10
7.1. Operational Considerations . . . . . . . . . . . . . . . 10
7.2. Management Considerations . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11
10.2. 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.
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In recent years new applications have been introduced which 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
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 which 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 which 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 describe 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.
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
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 to be defined in an
application specific scope.
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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 Bit-Mask (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User Defined Application Bit-Mask (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attribute sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Application Specific Link Attributes TLV
where:
o Type: TBD (see IANA Considerations Section 6)
o Length: variable.
o SABML : 1 octet value carrying the Standard Application Bit-Mask
Length in multiples of 4 octets. If the Standard Application Bit-
Mask is not present, the SABML MUST be set to 0.
o UDABML : 1 octet value carrying the User Defined Application Bit-
Mask Length in multiples of 4 octets. If the User Defined
Application Bit-Mask is not present, the UDABML MUST be set to 0.
o Standard Application Bit-Mask : variable size in multiple of 4
octets and 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].
o User Defined Application Bit-Mask : variable size in multiple of 4
octets and 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 are left to
implementation specifics.
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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 specific bitmasks) indicate 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 is
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 which 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) | |
| 1090 | Max Reservable | [RFC7752] |
| | Bandwidth | |
| 1091 | Unreserved Bandwidth | [RFC7752] |
| 1092 | TE Metric | [RFC7752] |
| 1096 | SRLG | [RFC7752] |
| 1114 | Unidirectional link | [I-D.ietf-idr-te-pm-bgp] |
| | delay | |
| 1115 | Min/Max | [I-D.ietf-idr-te-pm-bgp] |
| | Unidirectional link | |
| | delay | |
| 1116 | Unidirectional link | [I-D.ietf-idr-te-pm-bgp] |
| | delay variation | |
| 1117 | Unidirectional | [I-D.ietf-idr-te-pm-bgp] |
| | packet loss | |
| 1118 | Unidirectional | [I-D.ietf-idr-te-pm-bgp] |
| | residual bandwidth | |
| 1119 | Unidirectional | [I-D.ietf-idr-te-pm-bgp] |
| | available bandwidth | |
| 1120 | Unidirectional | [I-D.ietf-idr-te-pm-bgp] |
| | 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 be continued to be used at the top-level in the BGP-LS
Attribute for carrying attributes specific to RSVP-TE/GMPLS
application 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, down the line,
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.
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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.
Only application specific link attributes need to be advertised
within the ASLA TLV. Link attributes which 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 is described further in Section 5.
The BGP-LS originator learns of the association of an application
specific attribute to one or more set of applications from either the
underlying IGP protocol LSA/LSPs from which it is sourcing 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 flooding of 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 respective protocols.
A BGP-LS originator node which is sourcing link-state information
from the underlying IGP determines the mechanism of flooding
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 only (i.e. without any
ASLA sub-TLV) MUST be encoded using the respective BGP-LS top-
level TLVs listed in Table 1 (i.e. not within ASLA TLV). When
the IGP node is also SR enabled then another copy of application
specific link attributes SHOULD be also encoded as ASLA sub-TLVs
with the SR application bit for them. Further rules do not apply
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for such IGP nodes that do not use ASLA sub-TLVs in their
advertisements.
2. In case of IS-IS, when application specific link attributes are
received from a node with the L bit set in the ASLA sub-TLV then
the application specific link attributes are picked up from the
legacy ISIS TLVs/sub-TLVs and MUST be encoded within the BGP-LS
ASLA TLV as sub-TLVs with the application bitmask set as per the
IGP ASLA sub-TLV. When the ASLA sub-TLV with the L bit set also
has the RSVP-TE application bit set then the link attributes from
such an ASLA sub-TLV MUST be also encoded using the respective
BGP-LS top-level TLVs listed in Table 1 (i.e. not within ASLA
TLV).
3. In case of OSPFv2/v3, when application specific link attributes
are received from a node via TE LSAs then the application
specific link attributes from those LSAs MUST be encoded using
the respective BGP-LS TLVs listed in Table 1 (i.e. not within
ASLA TLV).
4. Application specific link attributes received from an IGP node
within its ASLA sub-TLV MUST be encoded in the BGP-LS ASLA TLV as
sub-TLVs with the application bitmask set as per the IGP
advertisement.
These rules ensure that a BGP-LS originator performs the translation
for all application specific link attributes from the IGP nodes into
the new BGP-LS ASLA TLVs irrespective of the IGP node supporting the
ASLA extension. Furthermore, it also ensures that BGP-LS TLVs
defined for RSVP-TE and GMPLS applications continue to be used for
those respective applications.
A BGP-LS consumer node always gets all 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.
5. Backward Compatibility
When it comes to BGP-LS, the backward compatibility aspects are
associated with the originators (i.e. nodes) and consumers (e.g.
PCE, controllers, applications, etc.) of the topology information.
The originators of BGP-LS information need to ensure that their
encoding of application specific link attributes is done such that
consumers running BGP-LS implementations without this specification
support can still support existing applications like RSVP-TE and SR.
The consumers running BGP-LS implementations that support this
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specification should also be able to work with BGP-LS originators
that do not support this specification and vice versa.
BGP-LS implementations have been originating link attributes and
consuming them without any application specific scoping. While the
ASLA TLV can be used without any backward compatibility
considerations for any new application (e.g. IGP Flexible Algorithm)
specific attribute advertisements, for existing applications like
RSVP-TE and SR some backward compatibility aspects need to be taken
care of.
This requires the introduction of a "compatibility mode" of
operations at originators of BGP-LS information for encoding of
information such that older implementations of BGP-LS consumers can
still support applications like RSVP-TE and SR. In addition to the
rules specified in Section 4, the following rules are to be followed
when operating in "compatibility mode" :
o Application specific link attribute received in IGP ASLA sub-TLVs,
corresponding to RSVP-TE or SR applications, MUST be also encoded
in their existing top level TLVs (as listed in Table 1) outside of
the ASLA TLV in addition to them being also advertised within the
ASLA TLV
o When the same application specific attribute, received in IGP ASLA
sub-TLVs, has different values for RSVP-TE and SR applications
then the value for RSVP-TE application SHOULD be preferred over
the value for SR application for advertisement as the top level
TLV (as listed in Table 1). An implementation MAY provide a knob
to reverse this preference.
It is RECOMMENDED that implementations operate in "compatibility
mode" by default. Implementations SHOULD have a knob for turning the
"compatibility mode" on or off. Operators MAY turn the
"compatibility mode" off when they are assured that all BGP-LS
consumers have been upgraded to support the extensions in this
document.
It is RECOMMENDED that the nodes which support this specification are
selected as originators of BGP-LS information when sourced from the
IGPs.
A BGP-LS consumer which does not implement this specification will
ignore the ASLA TLV and instead continue to use the attributes from
the existing top level TLVs.
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A BGP-LS consumer which implements this specification SHOULD prefer
the application specific attribute value received via sub-TLVs within
the ASLA TLV over the value received via the top level TLVs.
6. IANA Considerations
This document requests assigning code-points from the registry "BGP-
LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs" based on table below. 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 |
+------------+------------------------------------------+----------+
| TBD | Application Specific Link Attributes TLV | variable |
+------------+------------------------------------------+----------+
7. Manageability Considerations
This section is structured as recommended in [RFC5706].
The new protocol extensions introduced in this document augment the
existing IGP topology information that was distributed via [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 new TLVs for the
BGP-LS NLRI in this document.
7.1. Operational Considerations
No additional operation considerations are defined in this document.
7.2. Management Considerations
No additional management considerations are defined in this document.
8. Security Considerations
The new protocol extensions introduced in this document augment the
existing IGP topology information that was distributed via [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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9. Acknowledgements
The authors would like to thank Les Ginsberg for his review and
contributions to this work.
10. References
10.1. Normative References
[I-D.ietf-isis-te-app]
Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS TE Attributes per application", draft-
ietf-isis-te-app-05 (work in progress), October 2018.
[I-D.ietf-ospf-te-link-attr-reuse]
Psenak, P., Lindem, A., Ginsberg, L., Henderickx, W.,
Tantsura, J., Gredler, H., and J. Drake, "OSPF Link
Traffic Engineering (TE) Attribute Reuse", draft-ietf-
ospf-te-link-attr-reuse-06 (work in progress), November
2018.
[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>.
10.2. Informative References
[I-D.ietf-idr-eag-distribution]
Wang, Z., Wu, Q., and J. Tantsura, "Distribution of MPLS-
TE Extended admin Group Using BGP", draft-ietf-idr-eag-
distribution-08 (work in progress), October 2018.
[I-D.ietf-idr-te-pm-bgp]
Ginsberg, L., Previdi, S., Wu, Q., Tantsura, J., and C.
Filsfils, "BGP-LS Advertisement of IGP Traffic Engineering
Performance Metric Extensions", draft-ietf-idr-te-pm-
bgp-18 (work in progress), December 2018.
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[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-01 (work in progress), November 2018.
[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>.
Authors' Addresses
Ketan Talaulikar
Cisco Systems
Email: ketant@cisco.com
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Peter Psenak
Cisco Systems
Slovakia
Email: ppsenak@cisco.com
Jeff Tantsura
Apstra
Email: jefftant.ietf@gmail.com
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