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IGP Flexible Algorithms (Flexalgo) In IP Networks
draft-bonica-lsr-ip-flexalgo-00

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors William Britto , Shraddha Hegde , Parag Kaneriya , Rajesh Shetty , Ron Bonica
Last updated 2020-09-29
Replaced by draft-ietf-lsr-ip-flexalgo, RFC 9502
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draft-bonica-lsr-ip-flexalgo-00
LSR Working Group                                              W. Britto
Internet-Draft                                                  S. Hegde
Intended status: Standards Track                             P. Kaneriya
Expires: April 2, 2021                                         R. Shetty
                                                               R. Bonica
                                                        Juniper Networks
                                                      September 29, 2020

           IGP Flexible Algorithms (Flexalgo) In IP Networks
                    draft-bonica-lsr-ip-flexalgo-00

Abstract

   An IGP Flexible Algorithm computes a constraint-based path and maps
   that path to an identifier.  As currently defined, Flexalgo can only
   map the paths that it computes to Segment Routing (SR) identifiers.
   Therefore, Flexalgo cannot be deployed in the absence of SR.

   This document extends Flexalgo, so that it can map the paths that it
   computes to IP addresses.  This allows Flexalgo to be deployed in any
   IP network, even in the absence of SR.

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 April 2, 2021.

Copyright Notice

   Copyright (c) 2020 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

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   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.  Egress Node Procedures  . . . . . . . . . . . . . . . . . . .   3
   4.  Advertising Flexible Algorithm Definitions (FAD)  . . . . . .   3
   5.  Advertising IP Reachability Using a Flexalgo  . . . . . . . .   4
     5.1.  The ISIS IPv4 Flexalgo Prefix Reachability TLV  . . . . .   4
     5.2.  The ISIS IPv6 Flexalgo Prefix Reachability TLV  . . . . .   5
     5.3.  The ISIS MT IPv4 Flexalgo Prefix Reachability TLV . . . .   5
     5.4.  The ISIS MT IPv6 Flexalgo Prefix Reachability TLV . . . .   6
     5.5.  The OSPFv2 Flexalgo IP Prefix Opaque LSA  . . . . . . . .   6
   6.  Advertising IGP Algorithm Support . . . . . . . . . . . . . .   8
     6.1.  The ISIS IGP Algorithm Sub-TLV  . . . . . . . . . . . . .   8
     6.2.  The OSPFv2 IGP Algorithm TLV  . . . . . . . . . . . . . .   9
   7.  Advertising Link Attributes . . . . . . . . . . . . . . . . .  10
   8.  Calculating Constraint-Based Paths  . . . . . . . . . . . . .  10
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  11
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     12.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   An IGP Flexible Algorithm (Flexalgo) [I-D.ietf-lsr-flex-algo]:

   o  Computes a constraint-based path to an egress node.

   o  Maps that path to an identifier.

   As currently defined, Flexalgo can only map the paths that it
   computes to:

   o  A Segment Routing (SR) [RFC8402] Segment Identifier (SID).

   o  An SRv6 [I-D.ietf-spring-srv6-network-programming] locator.

   Therefore, Flexalgo cannot be deployed in the absence of SR and SRv6.

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   This document extends Flexalgo, allowing it to map the paths that it
   computes to:

   o  An IPv4 [RFC0791] address.

   o  An IPv6 [RFC8200] address.

   This allows Flexalgo to be deployed in any IP network, even in the
   absence of SR and SRv6.

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

3.  Egress Node Procedures

   Network operators configure multiple loopback interfaces on an egress
   node.  They can associate each loopback interface with:

   o  Zero or more IP addresses.

   o  Zero or one Flexible Algorithms.

   If an IP address and a Flexible Algorithm are associated with the
   same interface, they are also associated with one another.  An IP
   address MAY be associated with, at most, one interface.

   If a packet is sent to a loopback address, and the loopback address
   is not associated with a Flexible Algorithm, the packet follows the
   IGP least-cost path to the egress node.  If a packet is sent to a
   loopback address, and the loopback address is associated with a
   Flexible Algorithm, the packet follows the constraint-base path that
   the Flexible Algorithm calculated.

4.  Advertising Flexible Algorithm Definitions (FAD)

   To guarantee loop free forwarding, all routers that participate in a
   Flexible Algorithm MUST agree on the Flexible Algorithm Definition
   (FAD).

   Selected nodes within the IGP domain MUST advertise FADs as described
   in Sections 5, 6 and 7 of [I-D.ietf-lsr-flex-algo].

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5.  Advertising IP Reachability Using a Flexalgo

   ISIS [ISO10589] nodes use the following TLVs to advertise prefix
   reachability to prefixes that are associated with a Flexible
   Algorithm.

   o  The IPv4 Flexalgo Prefix Reachability TLV

   o  The IPv6 Flexalgo Prefix Reachability TLV

   o  The MT IPv4 Flexalgo Prefix Reachability TLV

   o  The MT IPv6 Flexalgo Prefix Reachability TLV

   OSPFv2 [RFC2328] nodes use the OSPFv2 Flexalgo IP Prefix Opaque LSA
   to advertise prefix reachability to prefixes that are associated with
   a Flexible Algorithm.

5.1.  The ISIS IPv4 Flexalgo Prefix Reachability TLV

      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     |U|   Reserved  |Flex-Algorithm |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Metric                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Prefix Len   |  Prefix ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Sub-TLV Len(*) | Sub-TLVs(*) ...

      * - if present

         Figure 1: The ISIS IPv4 Flexalgo Prefix Reachability TLV

   Figure 1 represents the ISIS IPv4 Flexalgo Prefix Reachability TLV.
   It contains the following fields:

   o  Type (8 bits): IPv4 Flexalgo Prefix Reachability TLV.  Value TBD
      by IANA.

   o  Length (8 bits) : TLV length.  Measured in bytes.

   o  U (1 bit): Set indicates up.  Clear indicates down.

   o  Reserved (7 bits): SHOULD be set to 0 by sender.  MUST be ignored
      by receiver.

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   o  Flex-Algorithm (8 bits): Flexible Algorithm mapped to a prefix.

   o  Metric (32 bits): As described in [RFC5305].

   o  Prefix Len (8 bits): Prefix length measured in bits.

   o  Prefix (variable length): Prefix mapped to Flexible Algorithm.

   o  Sub-TLV Len (8 bits): Optional.  Sub-TLV length in bytes.

   o  Sub-TLVs (variable length): Optional

5.2.  The ISIS IPv6 Flexalgo Prefix Reachability TLV

   The ISIS IPv6 Flexalgo Prefix Reachability TLV is identical to the
   ISIS IPv4 Flexalgo Prefix Reachability TLV except that it has a
   unique type, The type is TBD by IANA.

5.3.  The ISIS MT IPv4 Flexalgo Prefix Reachability TLV

        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     |     Reserved  |     MTID      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Flex-Algorithm |U|  Reserved   |            Metric ..          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         .. Metric             |  Prefix Len   |  Prefix ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Sub-TLV Len(*) | Sub-TLVs(*) ...

       * - if present

        Figure 2: The ISIS MT IPv4 Flexalgo Prefix Reachability TLV

   Figure 2 represents the ISIS MT IPv4 Flexalgo Prefix Reachability
   TLV.  It contains the following fields:

   o  Type (8 bits): MT IPv4 Flexalgo Prefix Reachability TLV.  Value
      TBD by IANA.

   o  Length (8 bits) : TLV length.  Measured in bytes.

   o  Reserved (8 bits): SHOULD be set to 0 by sender.  MUST be ignored
      by receiver.

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   o  MTID: Multitopology Identifier as defined in [RFC5120].  Note that
      the value 0 is legal.

   o  Flex-Algorithm (8 bits): Flexible Algorithm mapped to a prefix.

   o  U (1 bit): Set indicates up.  Clear indicates down.

   o  Reserved (7 bits): SHOULD be set to 0 by sender.  MUST be ignored
      by receiver.

   o  Metric (32 bits): As described in [RFC5305].

   o  Prefix Len (8 bits): Prefix length measured in bits.

   o  Prefix (variable length): Prefix mapped to Flexible Algorithm.

   o  Sub-TLV Len (8 bits): Optional.  Sub-TLV length in bytes.

   o  Sub-TLVs (variable length): Optional

5.4.  The ISIS MT IPv6 Flexalgo Prefix Reachability TLV

   The ISIS MT IPv6 Flexalgo Prefix Reachability TLV is identical to the
   ISIS MT IPv4 Flexalgo Prefix Reachability TLV except that it has a
   unique type, The type is TBD by IANA.

5.5.  The OSPFv2 Flexalgo IP Prefix Opaque LSA

   The Flexalgo IP Prefix Opaque LSA begins with the standard LSA header
   (Figure 3).  It contains the OSPFv2 Flexalgo IP Prefix TLV
   (Figure 4).

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        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            LS age             |     Options   |    10 or 11   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      11       |                    0                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Advertising Router                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     LS sequence number                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         LS checksum           |             length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +-                            TLVs                             -+
       |                             ...                               |

                       Figure 3: Standard LSA Header

             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(1)          |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Reserved   |  Prefix Length  |     MT-ID     |Flex-Algorithm |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Metric                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Prefix (variable)                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Sub-TLVs (variable)                      |
    +-                                                             -+
    |                             ...                               |

                  Figure 4: OSPFv2 Flexalgo IP Prefix TLV

   Figure 4 represents the OSPFv2 Flexalgo IP Prefix TLV.  It contains
   the following fields:

   o  Type (8 bits): MT IPv4 Flexalgo Prefix Reachability TLV.  Value
      TBD by IANA.

   o  Length (8 bits) : TLV length.  Measured in bytes.

   o  Reserved (8 bits): SHOULD be set to 0 by sender.  MUST be ignored
      by receiver.

   o  Prefix Len (8 bits): Prefix length measured in bits.

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   o  MTID: Multitopology Identifier as defined in [RFC4915].  Note that
      the value 0 is legal.

   o  Flex-Algorithm (8 bits): Flexible Algorithm mapped to a prefix.

   o  Metric (32 bits): As described in [RFC3630].

   o  Prefix (variable length): Prefix mapped to Flexible Algorithm.

   o  Sub-TLVs (variable length): Optional

6.  Advertising IGP Algorithm Support

   A node may use various algorithms when calculating paths.  Algorithm
   values are defined in the IGP Algorithm Type Registry [IANA-ALG].
   The following values have been defined:

   1.  SPF algorithm based on link metric.  This is the well-known
       shortest path algorithm as computed by the IS-IS Decision
       Process.  Consistent with the deployed practice for link-state
       protocols, algorithm 0 permits any node to overwrite the SPF path
       with a different path based on local policy.

   2.  Strict SPF algorithm based on link metric.  The algorithm is
       identical to algorithm 0, but algorithm 1 requires that all nodes
       along the path will honor the SPF routing decision.  Local policy
       MUST NOT alter the forwarding decision computed by algorithm 1 at
       the node claiming to support algorithm 1.

   ISIS and OSPFv2 use an IGP Algorithm TLV or sub-TLV to advertise IGP
   Algorithms that they support.

6.1.  The ISIS IGP Algorithm Sub-TLV

   The IGP Algorithm Sub-TLV is advertised in the ISIS Router Capability
   TLV.  The Router Capability TLV specifies flags that control its
   advertisement.  The IGP Algorithm MUST be propagated throughout the
   level and MUST NOT be advertised across level boundaries.  Therefore,
   Router Capability TLV distribution flags are set accordingly, i.e.,
   the S-Flag MUST NOT be set.

   The IGP Algorithm sub-TLV is optional.  It MUST NOT be advertised
   more than once at a given level.  A router receiving multiple IGP
   Algorithm sub-TLVs from the same originator SHOULD select the first
   advertisement in the lowest-numbered LSP.

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   When the originating router does not advertise the IGP Algorithm sub-
   TLV, it implies that algorithm 0 is the only algorithm supported by
   the routers that support the extensions defined in this document.

   When the originating router does advertise the IGP Algorithm sub-TLV,
   then algorithm 0 MUST be present while non-zero algorithms MAY be
   present.

        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    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Algorithm 1   |  Algorithm 2  | Algorithm ... |  Algorithm n  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 5: ISIS IGP Algorithm Sub-TLV

   Figure 5 depicts the IGP Algorithm Sub-TLV where:

   o  Type: IGP Algorithm (Value TBD by IANA)

   o  Length: Variable

   o  Algorithm: 1 octet of algorithm.

6.2.  The OSPFv2 IGP Algorithm TLV

   The IGP Algorithm TLV is a top-level TLV of the Router Information
   Opaque LSA [RFC7770].

   The IGP Algorithm TLV is optional.  It SHOULD only be advertised once
   in the Router Information Opaque LSA.  If the IGP Algorithm TLV is
   not advertised by the node, the node is assumed to support algorithm
   0 only.

   When multiple IGP Algorithm TLVs are received from a given router,
   the receiver MUST use the first occurrence of the TLV in the Router
   Information Opaque LSA.  If the IGP Algorithm TLV appears in multiple
   Router Information Opaque LSAs that have different flooding scopes,
   the IGP Algorithm TLV in the Router Information Opaque LSA with the
   area-scoped flooding scope MUST be used.  If the IGP Algorithm TLV
   appears in multiple Router Information Opaque LSAs that have the same
   flooding scope, the IGP Algorithm TLV in the Router Information (RI)
   Opaque LSA with the numerically smallest Instance ID MUST be used and
   subsequent instances of the IGP Algorithm TLV MUST be ignored.

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   The RI LSA can be advertised at any of the defined opaque flooding
   scopes (link, area, or Autonomous System (AS)).  For the purpose of
   IGP Algorithm TLV advertisement, area-scoped flooding is REQUIRED.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Algorithm 1 | Algorithm...  |   Algorithm n |               |
      +-                                                             -+
      |                                                               |
      +                                                               +

                    Figure 6: OSPFv2 IGP Algorithm TLV

   Figure 6 depicts the IGP Algorithm TLV where:

   o  Type: IGP Algorithm (Value TBD by IANA)

   o  Length: Variable

   o  Algorithm: 1 octet of algorithm.

7.  Advertising Link Attributes

   Various link attributes may be used during the Flex-Algorithm path
   calculation.  Section 12 of [I-D.ietf-lsr-flex-algo] describes link
   advertisement procedures.

8.  Calculating Constraint-Based Paths

   Nodes calculate constraint-based paths as described in Section 12 of
   [I-D.ietf-lsr-flex-algo].

9.  IANA Considerations

   This specification updates the OSPF Router Information (RI) TLVs
   Registry as follows:

                 +-------+---------------+---------------+
                 | Value | TLV Name      | Reference     |
                 +-------+---------------+---------------+
                 | TBD   | IGP Algorithm | This Document |
                 +-------+---------------+---------------+

   This document also updates the "Sub-TLVs for TLV 242" registry as
   follows:

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                 +-------+---------------+---------------+
                 | Value | TLV Name      | Reference     |
                 +-------+---------------+---------------+
                 | TBD   | IGP Algorithm | This Document |
                 +-------+---------------+---------------+

   This document also updates the "ISIS TLV Codepoints Registry"
   registry as follows:

   +-------+------------------------------------------+---------------+
   | Value | TLV Name                                 | Reference     |
   +-------+------------------------------------------+---------------+
   | TBD   | IPv4 Flexalgo Prefix Reachability TLV    | This document |
   | TBD   | IPv6 Flexalgo Prefix Reachability TLV    | This document |
   | TBD   | MT IPv4 Flexalgo Prefix Reachability TLV | This document |
   | TBD   | MT IPv6 Flexalgo Prefix Reachability TLV | This document |
   +-------+------------------------------------------+---------------+

   This document updates the "Opaque Link-State Advertisements (LSA)
   Option Types" registry as follows::

     +-------+---------------------------------------+---------------+
     | Value | TLV Name                              | Reference     |
     +-------+---------------------------------------+---------------+
     | TBD   | OSPFvv2 Flexalgo IP Prefix Opaque LSA | This Document |
     +-------+---------------------------------------+---------------+

10.  Security Considerations

   TBD

11.  Acknowledgements

   TBD.

12.  References

12.1.  Normative References

   [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-11 (work in progress), September 2020.

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   [ISO10589]
              IANA, "Intermediate system to Intermediate system routing
              information exchange protocol for use in conjunction with
              the Protocol for providing the Connectionless-mode Network
              Service (ISO 8473)", August 1987, <ISO/IEC 10589:2002>.

   [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>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [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>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [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>.

   [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>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

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   [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>.

   [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>.

12.2.  Informative References

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-20 (work in
              progress), September 2020.

   [IANA-ALG]
              IANA, "Sub-TLVs for TLV 242 (IS-IS Router CAPABILITY
              TLV)", August 1987, <https://www.iana.org/assignments/igp-
              parameters/igp-parameters.xhtml#igp-algorithm-types>.

   [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

   William Britto
   Juniper Networks
   Elnath-Exora Business Park Survey
   Bangalore, Karnataka  560103
   India

   Email: bwilliam@juniper.net

   Shraddha Hegde
   Juniper Networks
   Elnath-Exora Business Park Survey
   Bangalore, Karnataka  560103
   India

   Email: shraddha@juniper.net

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   Parag Kaneriya
   Juniper Networks
   Elnath-Exora Business Park Survey
   Bangalore, Karnataka  560103
   India

   Email: pkaneria@juniper.net

   Rejesh Shetty
   Juniper Networks
   Elnath-Exora Business Park Survey
   Bangalore, Karnataka  560103
   India

   Email: mrajesh@juniper.net

   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia  20171
   USA

   Email: rbonica@juniper.net

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