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Versions: 00 01                                                         
IDR                                                            S. Sangli
Internet-Draft                                                  S. Hegde
Intended status: Standards Track                                  R. Das
Expires: January 10, 2022                          Juniper Networks Inc.
                                                             B. Decraene
                                                                  Orange
                                                           July 09, 2021


                 Generic Metric for the AIGP attribute
              draft-ssangli-idr-bgp-generic-metric-aigp-00

Abstract

   This document defines extensions to the AIGP attribute to carry
   Generic Metric sub-types.  This is applicable when multiple domains
   exchange BGP routing information.  The extension will aid in intent-
   based end-to-end path selection.

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 10, 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Multiple Metric types . . . . . . . . . . . . . . . . . . . .   4
   4.  Generic Metric TLV  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Usage of Generic-Metric TLV . . . . . . . . . . . . . . . . .   5
   6.  Updates to Decision Procedure . . . . . . . . . . . . . . . .   6
   7.  Use-case: Different Metrics across Domains  . . . . . . . . .   7
   8.  Deployment Considerations . . . . . . . . . . . . . . . . . .   8
   9.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     13.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Large Networks belonging to an enterprise may consist of nodes in the
   order of thousands and may span across multiple IGP domains where
   each domain can run separate IGPs or levels/areas.  BGP may be used
   to interconnect such IGP domains, with one or more IGP domains within
   an Autonomous System.  The enterprise network can have multiple
   Autonomous Systems and BGP may be employed to provide connectivity
   between these domains.  Furthermore, BGP can be used to provide
   routing over a large number of such independent administrative
   domains.

   The traffic types have evolved over years and operators have resorted
   to defining different metric types within a IGP domain (ISIS or OSPF)
   for IGP path computation.  An operator may wish for intent-based end-
   to-end path selection.  The intent can be bandwidth or delay for
   example, and need to select paths across multiple domains satisfying
   the high-bandwidth or low-delay paths.  The intent is expressed as
   metric types and metric values.  Some metrics can be assigned
   administratively by an operator and they are described in the base
   ISIS, OSPF specifications.  Other metrics, for example, are the
   Traffic Engineering Default Metric defined in [RFC5305] and
   [RFC3630], Min Unidirectional delay metric defined in [RFC8570] and
   [RFC7471].  There may be other metrics such as jitter, reliability,
   fiscal cost, etc. that an operator may wish to express as the cost of




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   a link.  The procedures mentioned in the above specifications
   describe the IGP path computation within IGP domains.

   With the advent of 5G applications and Network Slicing applications,
   an operator may wish to provision end-to-end paths across multiple
   domains to cater to traffic constraints.  This is also known as
   intent-based inter-domain routing and there are certain architectures
   being developed as described in
   [I-D.hegde-spring-seamless-sr-architecture] and
   [I-D.dskc-bess-bgp-car-problem-statement].  The transport planes as
   described in [I-D.kaliraj-idr-bgp-classful-transport-planes] and
   color-based routing as described in [I-D.dskc-bess-bgp-car] describe
   how end-to-end intent-based paths can be established.  The proposal
   described in this document can be used in conjunction with such
   architectures.

   When multiple domains are interconnected via BGP, protocol extensions
   for advertising best-external path and/or ADDPATH as described in
   [RFC7911] are employed to take advantage of network connectivity thus
   providing alternate paths.  The color-based routing and Transport
   Plane routing proposals result in alternate paths for a reaching a
   destination.  During the BGP bestpath computation, the step(e) as per
   section 9.1.2.2 of [RFC4271], the interior cost of a route as
   determined via the IGP metric value can be used to break the tie.  In
   a network spanning multiple IGP domains, the AIGP TLV encoded within
   the AIGP attribute described in [RFC7311] can be used to compute the
   AIGP-enhanced interior cost to be used in the decision process for
   selecting the bestpath as documented in section 2 of [RFC7311].  The
   [RFC7311] specifies how AIGP TLV can carry the accumulated IGP metric
   value.

   There is a need to synchronize the metric-type values carried between
   IGP and BGP in order to avoid operational overhead of translation
   between them.  The existing AIGP TLV carries a TLV type and metric-
   value where TLV type does not map to IGP metric-types defined in the
   IGP metric-type registry.  Hence there is a need to provide a generic
   metric template to embed the IGP metric-type values within the AIGP
   attribute.  This document extends the AIGP attribute for carrying
   Generic-Metric TLV and the well-defined sub metric types.  This
   document also provides procedures for handling Generic-Metric during
   the BGP bestpath computation.

2.  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




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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Multiple Metric types

   Consider the network as shown in Figure 1.  The network has multiple
   domains.  Each domain runs a separate IGP instance.  Within each
   domain iBGP sessions are established between the PE routers. eBGP
   sessions are established between the Border Routers across domains.
   An operator wishes to compute end-to-end path optimized for a metric-
   type delay.  Each domain will be enabled to compute the IGP paths
   based on metric-type delay.  Such values should also be propagated to
   the adjacent domains for effective end-to-end path computation.


              ------IBGP-----EBGP------IBGP------EBGP------IBGP-----
              |             |     |             |     |             |

              +-------------+     +-------------+     +-------------+
              |             |     |             |     |             |
              |          ASBR1+--+ASBR2      ASBR3+--+ASBR4         |
              |             | . . |             | . . |             |
           PE1+   Domain1   |  .  |   Domain2   |  .  |   Domain3   +PE2
              |             | . . |             | . . |             |
              |          ASBR5+--+ASBR6      ASBR7+--+ASBR8         |
              |             |     |             |     |             |
              +-------------+     +-------------+     +-------------+


              |----ISIS1----|     |----ISIS2----|     |----ISIS3----|




                           Figure 1: WAN Network

   The AIGP TLV in the AIGP attribute as specified in [RFC7311] supports
   the IGP default metric.  If all domains use IGP cost as the metric,
   then one can compute the end-to-end path with shortest IGP cost.
   However if an operator wishes to compute the end-to-end path with
   metric other than IGP cost, we need additional extensions to the AIGP
   attribute for carry the metric-types and metric values.

   The [I-D.ietf-lsr-flex-algo-bw-con] proposes a generic metric type
   that can embed multiple metric types within it.  It supports both
   standard metric-types and user-defined metric-types.  This document
   leverages the generic-metric draft and proposes extensions to the
   AIGP attribute to carry Generic Metric TLV as specified below.



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4.  Generic Metric TLV

   This document proposes a new TLV : Generic-Metric TLV in the AIGP
   attribute.  This will carry the metric type and metric value used in
   the network.  The format is shown below.


        0                 1                   2                   3
        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 2
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |     Type    |             Length            |  metric-type  |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |              metric-value                                   |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+..........................


                       Figure 2: Generic-Metric TLV

      Generic-Metric TLV Type (1 octet): Code point to be assigned by
      IANA

      Generic-Metric TLV Length (2 octets): 9 or more

      Generic-Metric TLV Value (9 octets): 2 sub-fields as shown below:

      1. metric-type (1 octet): Value from IGP metric-type registry.

      2. metric-value (8 octets): Value range (0 - 0xffffffffffffffff)

5.  Usage of Generic-Metric TLV

   When a BGP speaker wishes to generate AIGP attribute with Generic-
   Metric TLV for a prefix, it MUST perform the following procedures.

      1.  The procedures specified in [RFC7311] section 3.4 should be
      followed that describes creation of attribute, modifications by
      the originator and non-originator of the route.

      2.  If the difference between the new metric-value and the
      advertised metric-value is less than the configured threshold, the
      update MAY be suppressed.  If the new metric-value is above the
      configured threshold, a new BGP update containing the new metric-
      value SHOULD be advertised.

      3.  If the domain uses a metric type other than IGP cost for the
      IGP path computation, the BGP speaker MAY add Generic-Metric TLV
      to the AIGP attribute before advertising to a neighboring BGP
      speaker.



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      4.  The metric-type sub-field in the Generic-Metric TLV will carry
      the value indicating the type of the metric as specified in the
      IGP metric-type registry.

      5.  The value of the metric or cost to reach the prefix being
      advertised will be encoded in the metric-value sub-field.  This is
      the cost or the distance to the destination prefix from the
      advertising BGP speaker which sets itself as the next hop as
      described in section 3.4 of [RFC7311].

      6.  Procedures for defining the cost to reach a next hop for
      various metric-types is outside the scope of this document.

   When a BGP speaker wishes to send a BGP update attaching the AIGP
   attribute, it must validate if that session has been enabled for
   sending the AIGP attribute as per procedures mentioned in [RFC7311].

   When a BGP speaker receives a BGP update that has the AIGP attribute
   with Generic-Metric TLV it MUST perform the following procedures.

      1.  It must validate if that session has been enabled to receive
      the AIGP attribute as per rules mentioned in [RFC7311].

      2.  If the BGP speaker does not recognize the Generic-Metric TLV
      or type of metric encoded in metric-type subfield of the TLV, then
      the BGP speaker will ignore the Generic-Metric TLV and follow the
      BGP decision procedure as specified in [RFC7311].

      3.  If the metric-type matches with the type of the metric
      configured on the router, then the metric-value sub-field MUST be
      used in the AIGP-enhanced interior cost computation as specified
      in the next section.

      4.  If the metric-type does not match with the type of the metric
      configured on the router, then the BGP speaker may translate cost
      encoded in the metric-value field for computing the AIGP-enhanced
      interior cost specified in [RFC7311].  A policy may be used to
      provide the metric translation.

6.  Updates to Decision Procedure

   When a route has the AIGP attribute with Generic-Metric TLV and the
   metric-type sub-field matches with the type of the metric used in the
   current domain, the AIGP-enhanced interior cost should be computed as
   below.

      Let A be the value of the value of the metric-value sub-field of
      the Generic-Metric TLV.



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      Let m be the cost to reach the next hop that IGP uses for its path
      computation as described in [RFC7311].

      The AIGP-enhanced interior cost will be A+m as described in
      [RFC7311].

   If the type of the metric used in the domain does not match the
   metric-type sub-field of the Generic-Metric TLV, the metric-value may
   be translated to the type of the metric used in the domain.  The
   translated metric value can be zero.

   The translated metric value MUST be used in the AIGP-enhanced
   interior cost computation which will be used in the decision process
   as described in [RFC7311].

7.  Use-case: Different Metrics across Domains


                                   +--------------+
                                   |   Domain2    |
                                   |              |
                             ......+ASBR21  ASBR22+....
                             .     |              |   .
              +------------+ .     |  igp-metric  |   . +--------------+
              |  Domain1   | .     +--------------+   . |    Domain4   |
              |            | .                        . |              |
              |      ASBR11+..                        ..+ASBR41        |
              +PE1         |                            |           PE2+
              |      ASBR12+..                        ..+ASBR42        |
              |            | .                        . |              |
              | IGP-metric | .                        . | delay-metric |
              +------------+ .     +--------------+   . +--------------+
                             .     |   Domain3    |   .
                             .     |              |   .
                             ......+ASBR31  ASBR32+....
                                   |              |
                                   | delay-metric |
                                   +--------------+


                 Figure 3: Different metric across network

   Each domain is a separate Autonomous System.  Within each domain,
   ASBR and PE form iBGP peering.  The IGP within each domain uses
   domain specific metric.  Domain3 and Domain4 use delay as the metric
   while Domain1 and Domain2 use IGP cost as the metric.  ASBRs across
   domains form eBGP peering.  The use-case is to find delay-based end-
   to-end path from Domain1 to Domain4.



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   This can be achieved by the advertising router to add the AIGP
   attribute with metric type 1 that represents delay metric.  In the
   above network diagram, ASBR41 (and ASBR42) will advertise prefix
   PE2-loopback with Generic-Metric TLV with metric-type 1.  The metric-
   value sub-field of the Generic-Metric TLV will represent the cost to
   reach PE2's loopback end-point from the advertising router as they
   will do next hop self.

   In Domain3, when ASRB32 advertises the prefix PE2-loopback within the
   local domain, it may add cost to the metric-value, the value
   representing the delay introduced by the DMZ link between ASRB32 to
   ASBR42.  When ASRBR31 advertises the prefix PE2-lookback, it will
   perform the following procedures.

      1.  Compute the delay d of the path to reach ASBR32 from which it
      has chosen the bestpath.

      2.  Add the above d value to the metric-value sub-field of the
      Generic-Metric TLV.

   In Domain2 however, the local metric type IGP cost.  The ASBR22 may
   follow the procedure similar to ASBR32 and add the delay value
   corresponding to the DMZ link between ASBR22 and ASBR41 before
   advertising the path internally in Domain2.  When ASBR21 computes the
   AIGP-enhanced interior cost, as mentioned before, it may translate
   the igp cost to reach ASBR22 and may add the translated value to the
   delay-metric.  In the above network example, the delay cost from
   ASBR21 to ASBR22 is negligible and hence delay-metric value will be
   unchanged.

   The procedures for AIGP-enhanced interior cost computation at ASBR11
   (and ASBR12) will follow DMZ delay computation procedure described
   above.  PE1 will have two paths to reach PE2-loopback: P1 via ASBR11
   (and domain2) and P2 via ASBR12 (and domain3), each having respective
   AIGP-enhanced interior cost representing end-to-end delay.  The BGP
   decision process described in [RFC7311] will result in delay
   optimized end-to-end path for PE2-loopback on PE1 that can be used to
   resolve the service prefixes.

8.  Deployment Considerations

   It can be noted that a domain may translate the metric-value of the
   metric-type used in the local domain to the metric-type present in
   the Generic-Metric TLV.  The idea is to propagate the cost of
   reaching the prefix through the domain while maintaining the metric-
   type chosen by the originating router and domain.  The translation of
   metric types to the one carried in the AIGP attribute can be done via
   policy.  Definition of such policies and how they can be enforced is



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   outside the scope of this document.  In topologies where there is a
   common router between adjacent domains that do iBGP peering, the
   Border router can provide the translation.

   All routers of a domain MUST compute the AIGP-enhanced interior cost
   as described above to be used during decision process.  Within a
   domain, if one router R1 applies AIGP-enhanced interior cost while R2
   does not, it may lead to routing loop unless some sort of tunnelling
   technology viz MPLS, SRv6, IP, etc. is adopted to reach the next hop.
   In a network where any tunnelling technology is used, one can
   incrementally deploy the Generic-Metric functionality.  In a network
   without any tunnelling technology, it is recommended that all routers
   should support Generic-Metric based AIGP-enhanced interior cost
   computation.

9.  Backward Compatibility

   When a BGP speaker receives an update with the AIGP attribute it may
   have Generic-Metric TLV.  If the BGP speaker understands the AIGP
   attribute but does not understand the Generic-Metric TLV, it will
   process the AIGP attribute as per [RFC7311].  However when it needs
   to advertise the prefix to its peers it will pass on the AIGP
   attribute with all the TLVs including the unknown Generic-Metric TLV
   as per [RFC7311].  If a BGP speaker does not understand the Generic-
   Metric TLV, it may chose sub-optimal BGP path.

10.  Security Considerations

   This document does not introduce any new security considerations
   beyond those already specified in [RFC4271], [RFC7311].

11.  IANA Considerations

   IANA is requested to assign a code point for Generic Metric TLV.  The
   metric-type field refers to the IGP metric-type registry defined in
   [I-D.ietf-lsr-flex-algo-bw-con]

12.  Acknowledgements

   The authors would like to thank John Scudder and Jeff Haas for
   careful review and suggestions.

13.  References








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13.1.  Normative References

   [I-D.dskc-bess-bgp-car]
              Rao, D., Agrawal, S., Filsfils, C., Talaulikar, K.,
              Steinberg, D., Jalil, L., Su, Y., Guichard, J., Patel, K.,
              and H. Wang, "BGP Color-Aware Routing (CAR)", draft-dskc-
              bess-bgp-car-02 (work in progress), May 2021.

   [I-D.dskc-bess-bgp-car-problem-statement]
              Rao, D., Agrawal, S., Filsfils, C., Talaulikar, K.,
              Decraene, B., Steinberg, D., Jalil, L., Guichard, J.,
              Patel, K., and W. Henderickx, "BGP Color-Aware Routing
              Problem Statement", draft-dskc-bess-bgp-car-problem-
              statement-03 (work in progress), May 2021.

   [I-D.hegde-spring-seamless-sr-architecture]
              Hegde, S., Bowers, C., Xu, X., Gulko, A., Bogdanov, A.,
              Uttaro, J., Jalil, L., Khaddam, M., and A. Alston,
              "Seamless Segment Routing Architecture", draft-hegde-
              spring-seamless-sr-architecture-00 (work in progress),
              February 2021.

   [I-D.ietf-lsr-flex-algo-bw-con]
              Hegde, S., J, W. B. A., Shetty, R., Decraene, B., Psenak,
              P., and T. Li, "Flexible Algorithms: Bandwidth, Delay,
              Metrics and Constraints", draft-ietf-lsr-flex-algo-bw-
              con-00 (work in progress), May 2021.

   [I-D.kaliraj-idr-bgp-classful-transport-planes]
              Vairavakkalai, K., Venkataraman, N., Rajagopalan, B.,
              Mishra, G., Khaddam, M., Xu, X., and R. J. Szarecki, "BGP
              Classful Transport Planes", draft-kaliraj-idr-bgp-
              classful-transport-planes-07 (work in progress), February
              2021.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [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>.

   [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>.




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   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

13.2.  Informative References

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4659]  De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
              "BGP-MPLS IP Virtual Private Network (VPN) Extension for
              IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006,
              <https://www.rfc-editor.org/info/rfc4659>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC7311]  Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro,
              "The Accumulated IGP Metric Attribute for BGP", RFC 7311,
              DOI 10.17487/RFC7311, August 2014,
              <https://www.rfc-editor.org/info/rfc7311>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <https://www.rfc-editor.org/info/rfc7471>.







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   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <https://www.rfc-editor.org/info/rfc7911>.

   [RFC8277]  Rosen, E., "Using BGP to Bind MPLS Labels to Address
              Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
              <https://www.rfc-editor.org/info/rfc8277>.

   [RFC8570]  Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
              D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
              Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
              2019, <https://www.rfc-editor.org/info/rfc8570>.

Authors' Addresses

   Srihari Sangli
   Juniper Networks Inc.
   Exora Business Park
   Bangalore, KA  560103
   India

   Email: ssangli@juniper.net


   Shraddha Hegde
   Juniper Networks Inc.
   Exora Business Park
   Bangalore, KA  560103
   India

   Email: shraddha@juniper.net


   Reshma Das
   Juniper Networks Inc.
   1133 Innovation Way
   Sunnyvale, CA  94089
   USA

   Email: dreshma@juniper.net


   Bruno Decraene
   Orange
   France

   Email: bruno.decraene@orange.com



Sangli, et al.          Expires January 10, 2022               [Page 12]