Flexible Algorithm with Bandwidth Constrains
draft-lp-lsr-fa-bandwidth-00

Document Type Active Internet-Draft (individual)
Authors Liu Yao  , Shaofu Peng 
Last updated 2021-04-22
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LSR Working Group                                               Yao. Liu
Internet-Draft                                              Shaofu. Peng
Intended status: Standards Track                               ZTE Corp.
Expires: October 24, 2021                                 April 22, 2021

              Flexible Algorithm with Bandwidth Constrains
                      draft-lp-lsr-fa-bandwidth-00

Abstract

   This document proposes extensions for IGP to allow the computation
   based on bandwidth constraints together with the existing metric in
   Flexible Algorithm.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on October 24, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   3.  ISIS bandwidth  constraint Sub-TLV of ISIS FAD Sub-TLV  . . .   3
   4.  OSPF bandwidth  constraint Sub-TLV of ISIS FAD Sub-TLV  . . .   3
   5.  Calculation of Flex Algorithm Paths . . . . . . . . . . . . .   4
     5.1.  Calculation . . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Illustration  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
           TLV . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.2.  OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
           TLV . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   [I-D.ietf-lsr-flex-algo] defines the Flex-Algorithm as a set of
   parameters consisting of calculation-type, metric-type and a set of
   constraints.  The metric includes igp-metric, te-metric, delay-
   metric, and etc.

   While the calculation of a path based on metrics is accumulative,
   e.g, the path calculated based on the delay-metric is that with the
   smallest sum of the metrics of each link.  The bandwidth of a path
   depends on the link with the smallest bandwidth among the links that
   comprise the path.

   It's more appropriate that the bandwidth acts as a constraint instead
   of a metric in the path computation.

   This document proposes extensions for IGP to allow the computation
   based on bandwidth constraints together with the existing metric in
   FLex-Algo.

2.  Conventions used in this document

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP

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

3.  ISIS bandwidth constraint Sub-TLV of ISIS FAD Sub-TLV

   This document defines the ISIS bandwidth constraint Sub-TLV.  It is a
   Sub-TLV of the ISIS FAD Sub-TLV [I-D.ietf-lsr-flex-algo] and 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     |  BW-Con Type  |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: ISIS bandwidth constraint Sub-TLV

   where:

   o  Type: TBA

   o  Length: 1 octets

   o  BW-Con Type: 1 octets of bandwidth constraint information.

   The BW-Con Type has the following values:

   1: Choose the link with Maximum Link Bandwidth ( MLB defined in
   [RFC5305] ).

   2: Choose the link with maximum Unidirectional Available Bandwidth (
   UAB defined in [RFC8570] ).

   3: Choose the link with the lowest bandwidth utilization rate.

   The ISIS bandwidth constraint Sub-TLV MUST NOT appear more than once
   in an ISIS FAD Sub-TLV.  If it appears more than once, the ISIS FAD
   Sub-TLV MUST be ignored by the receiver.

4.  OSPF bandwidth constraint Sub-TLV of ISIS FAD Sub-TLV

   This document defines the OSPF bandwidth constraint Sub-TLV.  It is a
   Sub-TLV of the OSPF FAD Sub-TLV [I-D.ietf-lsr-flex-algo] and has the
   following format:

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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Type             |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  BW-Con Type  |   Reserved    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2: OSPF bandwidth constraint Sub-TLV

   where:

   o  Type: TBA

   o  Length: 1 octets

   o  BW-Con Type: 1 octets of bandwidth constraint information.

   The BW-Con Type has the following values:

   1: Choose the link with Maximum Bandwidth ( MB defined in [RFC3630]
   ).

   2: Choose the link with maximum Unidirectional Available Bandwidth (
   UAB defined in [RFC7471] ).

   3: Choose the link with the lowest bandwidth utilization rate.

   The OSPF bandwidth constraint Sub-TLV MUST NOT appear more than once
   in a OSPF FAD Sub-TLV.  If it appears more than once, the OSPF FAD
   Sub-TLV MUST be ignored by the receiver.

5.  Calculation of Flex Algorithm Paths

   Routes that don't support the bandwidth constraint Sub-TLV MUST NOT
   participate in the corresponding Flex-Algo plane.

   Existing rules for calculation of Flex-Algorithm paths specified in
   [I-D.ietf-lsr-flex-algo] are still applicable.

   As for the new bandwidth constraint, first, select the optimal
   path(s) only according to the bandwidth constraint.  If there are
   multiple candidate paths satisfying the bandwidth constraint, then
   select the best path based on the metric computation from these
   candidate paths.

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5.1.  Calculation

   The result of IGP flex algo shortest path calculation based on
   bandwidth constraints is that each participating node in flex algo
   plane constructs a SPT (with itself as the root) per algorithm, which
   contains all other participating nodes as destination nodes.

   Step1: Assume S is the root, and other nodes are D1, D2, D3,... Dn.

   Step2: Find all paths from source node S to destination node D1.
   Suppose there is one or more paths, and it is recorded as path-1,
   path-2,..., path-m, where m > =1.

   Step3: Initializes the current root node (cur-root) to S.  Take two
   paths (such as path-1 and path-2) to compare to see who is more
   qualified for the constraint.  Note that as mentioned above, the
   constraint conditions here refer to the combination of bandwidth
   constraint and metric, and compare based on bandwidth constraints
   firstly and then metric secondly.  This can be compared in segments,
   that is, from the current root node to the destination node, finding
   a first crossed node which appears in two paths at the same time and
   is recorded as the current branch (cur-branch) node.

   Step4: Compare the path segment from the current root node to the
   current branch node in the two paths to see who is more qualified for
   the path.  If one of the two path segments is optimal and the other
   is suboptimal, it means that one of the two paths is optimal than the
   other.  Add the optimal path to the "winning group".  Note that if
   the path of the suboptimal is originally in the "winning group", the
   "winning group" should be cleared firstly and then new optimal path
   is added.  The optimal path continues to compare with other paths,
   jump to Step3.

   Otherwise, if the two path fragments are both optimal, the current
   root node (cur root) is updated as the current branch node.  If the
   current root node reaches the destination node, the comparison is
   finished, and the two paths join the "winning group" to form ECMP
   (equal cost multi path equivalent multipath); otherwise, continue to
   find the next crossed node in the two paths as the new current branch
   node, and jump to Step4.

   Step5: The above result will get the shortest paths from S to D1.
   Similarly, repeating Step2 for destination D2, D3,..., Dn
   respectively will get the shortest path from S to D2, D3,..., Dn
   respectively.  Thus the shortest path tree with S as the root node in
   the flex algo plane is constructed.

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5.2.  Illustration

                               +----D----+
                               |         |
                        A------B         C
                               |         |
                               +----E----+

                       Figure 3: Reference Topology

   As shown in Figure 3, there're 5 nodes in the given FA plane, whose
   metric type is delay metric and the bandwidth constrain is to choose
   the link with the maximum total bandwidth.

   The bandwidth and metric for each link is shown in Table 1.

                       +------+-----------+--------+
                       | Link | Bandwidth | Metric |
                       +------+-----------+--------+
                       |  A-B |  100      |  10    |
                       |  B-D |  5        |  2     |
                       |  D-C |  10       |  2     |
                       |  B-E |  10       |  1     |
                       |  E-C |  5        |  1     |
                       +------+-----------+--------+

                       Table 1: Bandwidth and Metric

   It is required to calculate the optimal path from A to C in this FA
   plane.

   First, select the path who has the maximum bandwidth . Since the
   bandwidth of a path depends on the link with the smallest bandwidth,
   the maximum bandwidth s of path A-B-D-C and A-B-E-C are both 5.
   These two paths are chosen as candidate paths.

   Second, compare the metric values of the candidate paths.  The metric
   of path A-B-E-C is smaller, so it is chosen as the best path.

6.  Security Considerations

   TBD

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7.  IANA Considerations

7.1.  ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV

   Type: TBA

   Description: bandwidth constraint Sub-TLV

   Reference: This document.

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

   Type: TBA

   Description: bandwidth constraint Sub-TLV

   Reference: This document.

8.  References

8.1.  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-13 (work in progress), October 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

8.2.  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>.

   [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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   [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>.

   [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

   Liu Yao
   ZTE Corp.

   Email: liu.yao71@zte.com.cn

   Peng Shaofu
   ZTE Corp.

   Email: peng.shaofu@zte.com.cn

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