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IGP Flexible Algorithm with Link Loss
draft-wang-lsr-flex-algo-link-loss-02

Document Type Active Internet-Draft (individual)
Authors Wang Yifan , Guoqi Xu , Xuesong Geng , Jie Dong
Last updated 2024-03-22
Replaces draft-xu-lsr-flex-algo-link-loss
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draft-wang-lsr-flex-algo-link-loss-02
Network Working Group                                            Y. Wang
Internet-Draft                                                     G. Xu
Intended status: Standards Track                                 X. Geng
Expires: 23 August 2024                                          J. Dong
                                                                  Huawei
                                                        20 February 2024

                 IGP Flexible Algorithm with Link Loss
                 draft-wang-lsr-flex-algo-link-loss-02

Abstract

   IGP Flexible Algorithms allow IGPs to compute constraint-based paths.
   Since link packet loss rate plays an important role in network
   evaluation, links with high packet loss rate should be bypassed
   during forwarding.  This draft proposes a path computation method
   based on a maximum link loss constraint to prune unsatisfied links in
   Flexible Algorithms.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD 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
   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 23 August 2024.

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Copyright Notice

   Copyright (c) 2024 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 carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Exclude Maximum Link Loss Sub-TLV . . . . . . . . . . . . . .   3
     2.1.  IS-IS Exclude Maximum Link Loss Sub-TLV . . . . . . . . .   4
     2.2.  OSPF Exclude Maximum Link Loss Sub-TLV  . . . . . . . . .   5
   3.  Calculation of Flexible Algorithm Paths . . . . . . . . . . .   5
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  OSPF Sub-Sub-TLVs for Flexible Algorithm Definition
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Link packet loss rate (link loss) is a measure of the percentage of
   data packets that are lost during transmission over a network.  It is
   an important performance metric that directly impacts the quality of
   service, network congestion, security, and overall network
   efficiency.  Ensuring a low packet loss rate is essential for
   maintaining efficient and secure network operations.  Consequently,
   It is necessary to avoid passing through links with a high packet
   loss rate during forwarding.

   The link loss is advertised by the Unidirectional Link Loss Sub-TLV
   defined in [RFC8570] by IS-IS and [RFC7471] by OSPF, which describes
   the loss (as a packet percentage) between two directly connected IS-
   IS neighbors.  This Sub-TLV is carried in the Application-Specific
   Link Attributes Sub-TLV advertised by IS-IS [RFC9479] or OSPF

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   [RFC9492].  The link packet loss rate can be measured by methods such
   as TWAMP [RFC5357] and STAMP [RFC8762], which is beyond the scope of
   this document.

   IGP Flexible Algorithms allow IGPs to compute constraint-based paths
   [RFC9350].  Current path computation methods are based on calculating
   the minimum cost of the path from the source to the destination.
   Flex-Algorithm has already supported path computation with the IGP
   cost, the minimum link delay and the traffic-engineering metric.
   [I-D.ietf-lsr-flex-algo-bw-con] defines a family of generic metrics
   (e.g. bandwidth based metric type) and bandwidth related constraints
   to support path computation based on bandwidth.  However, current
   calculation types and metric types cannot support path computation
   based on link loss, since the cost of the path should be defined as
   the maximum/minimum value among all passing links.

   To overcome the above issue, there are two solutions.  First, new
   operators like maximum value operator can be defined, which works as
   a step function.  When the link loss exceeds a threshold, the cost of
   the link is set to the maximum.  Second, new Flexible Algorithm
   Definition (FAD) constraints can be defined to exclude links that do
   not meet the link loss requirements during path calculation.  The
   second method is specifically demonstrated in this document.  The
   general ideas are as below.

      1.  The link loss is used as a link constraint for path
      computation.  That is, the link whose loss rate is greater than
      the specified value is excluded.

      2.  Metric-type remains unchanged: igp, te, and delay.

   With a new FAD constraint Sub-TLV advertised by IGP, links with low
   packet loss rate will be selected for path computation.  The new
   Exclude Maximum Link Loss Sub-TLVs are defined in Section 2.  The
   Flex-Algorithm calculation method based on link loss is presented in
   Section 3.  Link packet loss rate is obtained from the existing
   Unidirectional Link Loss Sub-TLV defined in RFC9479 and RFC9492.

2.  Exclude Maximum Link Loss Sub-TLV

   A new Exclude Maximum Link Loss Sub-TLV is defined as a sub-TLV of
   the FAD TLV.  To guarantee loop free forwarding, all routers that
   participate in a Flex-Algorithm MUST agree on the FAD.  Selected
   nodes within the IGP domain MUST advertise FADs as described in
   Sections 5, 6, and 7 of [RFC9350].

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   The Exclude Maximum Link Loss Sub-TLV is proposed to specify the
   upper limit of the link loss.  When this Sub-TLV is carried in a FAD
   TLV, all links with packet loss rate larger than the defined maximum
   link loss value will be excluded from the Flex-Algorithm topology.

2.1.  IS-IS Exclude Maximum Link Loss Sub-TLV

   IS-IS Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
   sub-TLV of the IS-IS FAD sub-TLV.  It has the following format:

      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     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Max Link Loss                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Type: 252(TBA)

        Length: 3 octets

        Max Link Loss:  This 24-bit field carries link packet loss as a
      percentage of the total traffic sent over a configurable interval.
      The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%. This
      value is the highest packet-loss percentage that can be expressed.
      Therefore, measured values that are larger than the field maximum
      SHOULD be encoded as the maximum value.

                      Figure 1: IS-IS FAEML Sub-TLV

   The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV.  If it
   appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
   receiver.

   The maximum link loss advertised in FAEML Sub-TLV MUST be compared
   with the link loss advertised in Sub-Sub-TLV 36 [RFC8570] of ASLA
   Sub- TLV [RFC9479].  If L-Flag is set in the ASLA sub-TLV, the
   maximum link loss advertised in FAEML sub-TLV MUST be compared with
   the link loss advertised by the sub-TLV 36 of the TLV
   22/222/23/223/141 [RFC5305] as defined in [RFC9479] Section 4.2.

   If the link loss is larger than the maximum link loss advertised in
   FAEML sub-TLV, the link MUST be excluded from the Flex-Algorithm
   topology.  If a link does not have the link loss advertised but the
   FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the
   Flex-Algorithm topology.

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2.2.  OSPF Exclude Maximum Link Loss Sub-TLV

   OSPF Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
   sub-TLV of the OSPF FAD sub-TLV.  It has the following format:

      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           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Max Link Loss                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Type: 252(TBA)

        Length: 3 octets

        Max Link Loss:  This 24-bit field carries link packet loss as a
      percentage of the total traffic sent over a configurable interval.
      The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%. This
      value is the highest packet-loss percentage that can be expressed.
      Therefore, measured values that are larger than the field maximum
      SHOULD be encoded as the maximum value.

                       Figure 2: OSPF FAEML Sub-TLV

   The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV.  If it
   appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
   receiver.

   The maximum link loss advertised in FAEML Sub-TLV MUST be compared
   with the link loss advertised in Sub-Sub-TLV 30 [RFC7471] of ASLA
   Sub- TLV [RFC9492].  The ASLA Sub-TLV is advertised in Extended Link
   Opaque LSAs [RFC7684] for OSPFv2 and E-Router-LSAs [RFC8362] for
   OSPFv3.

   If the link loss is larger than the maximum link loss advertised in
   FAEML sub-TLV, the link MUST be excluded from the Flex-Algorithm
   topology.  If a link does not have the link loss advertised but the
   FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the
   Flex-Algorithm topology.

3.  Calculation of Flexible Algorithm Paths

   A new rule is added to the rules used to prune links from the
   topology during the Flex-Algorithm computation in Section 13 of
   [RFC9350].

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      1.  Check if any exclude FAEML rule is part of the Flex-Algorithm
      definition.  If such exclude rule exists and the link has link
      loss advertised, check if the link satisfies the FAEML rule.  If
      not, the link MUST be pruned from the computation.

4.  Operational Considerations

   In some scenarios, the link packet loss rate may fluctuate around the
   threshold value.  Consequently, the link status can be frequently
   changed between available and unavailable, which could lead to
   frequent flex-algo calculation.  To solve this problem, a suppression
   mechanism can be developed.  When the packet loss rate is detected on
   a frequent change, a timer can be set to delay the update process.

5.  IANA Considerations

5.1.  IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV

   Type: 252(TBA)

   Description: IS-IS Exclude Maximum Link Loss Sub-TLV

   Reference: This document Section 2.1

5.2.  OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV

   Type: 252(TBA)

   Description: OSPF Exclude Maximum Link Loss Sub-TLV

   Reference: This document Section 2.2

6.  References

6.1.  Normative References

   [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>.

   [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>.

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   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

   [RFC9350]  Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
              and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
              DOI 10.17487/RFC9350, February 2023,
              <https://www.rfc-editor.org/info/rfc9350>.

   [RFC9479]  Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS Application-Specific Link Attributes",
              RFC 9479, DOI 10.17487/RFC9479, October 2023,
              <https://www.rfc-editor.org/info/rfc9479>.

   [RFC9492]  Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
              J., and J. Drake, "OSPF Application-Specific Link
              Attributes", RFC 9492, DOI 10.17487/RFC9492, October 2023,
              <https://www.rfc-editor.org/info/rfc9492>.

6.2.  Informative References

   [I-D.ietf-lsr-flex-algo-bw-con]
              Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,
              P., and T. Li, "Flexible Algorithms: Bandwidth, Delay,
              Metrics and Constraints", Work in Progress, Internet-
              Draft, draft-ietf-lsr-flex-algo-bw-con-07, 26 September
              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
              lsr-flex-algo-bw-con-07>.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, DOI 10.17487/RFC5357, October 2008,
              <https://www.rfc-editor.org/info/rfc5357>.

   [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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   [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>.

   [RFC8762]  Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
              Two-Way Active Measurement Protocol", RFC 8762,
              DOI 10.17487/RFC8762, March 2020,
              <https://www.rfc-editor.org/info/rfc8762>.

Authors' Addresses

   Yifan Wang
   Huawei
   Huawei Bld., No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: wangyifan82@huawei.com

   Guoqi Xu
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China
   Email: xuguoqi@huawei.com

   Xuesong Geng
   Huawei
   Huawei Bld., No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: gengxuesong@huawei.com

   Jie Dong
   Huawei
   Huawei Bld., No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: jie.dong@huawei.com

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