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Flexible Algorithms Bandwidth Constraints
draft-hegde-lsr-flex-algo-bw-con-00

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Shraddha Hegde , William Britto , Rajesh Shetty , Bruno Decraene
Last updated 2021-02-22
Replaced by draft-ietf-lsr-flex-algo-bw-con
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draft-hegde-lsr-flex-algo-bw-con-00
SPRING                                                          S. Hegde
Internet-Draft                                                 W. Britto
Intended status: Standards Track                               R. Shetty
Expires: August 26, 2021                           Juniper Networks Inc.
                                                             B. Decraene
                                                                  Orange
                                                       February 22, 2021

               Flexible Algorithms Bandwidth Constraints
                  draft-hegde-lsr-flex-algo-bw-con-00

Abstract

   Many networks configure the link metric relative to the link
   capacity.  High bandwidth traffic gets routed as per the link
   capacity.  Flexible algorithms provides mechanisms to create
   constraint based paths in IGP.  This draft documents a set of
   bandwidth related constraints to be used 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 RFC 2119 [RFC2119].

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
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   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 August 26, 2021.

Copyright Notice

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

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   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 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Bandwidth Metric adevertisement . . . . . . . . . . . . . . .   3
     2.1.  ISIS Bandwidth Metric sub-TLV . . . . . . . . . . . . . .   3
     2.2.  OSPF Bandwidth Metric sub-TLV . . . . . . . . . . . . . .   4
   3.  FAD constraint sub-TLVs . . . . . . . . . . . . . . . . . . .   5
     3.1.  ISIS FAD constraint sub-TLVs  . . . . . . . . . . . . . .   6
       3.1.1.  ISIS Exclude Minimum Bandwidth sub-TLV  . . . . . . .   6
       3.1.2.  ISIS Exclude Maximum Delay sub-TLV  . . . . . . . . .   6
     3.2.  OSPF FAD constraint sub-TLVs  . . . . . . . . . . . . . .   7
       3.2.1.  OSPF Exclude Minimum Bandwidth sub-TLV  . . . . . . .   7
       3.2.2.  OSPF Exclude Maximum Delay  sub-TLV . . . . . . . . .   8
   4.  Automatic metric calculation  . . . . . . . . . . . . . . . .   9
     4.1.  Simple mode . . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  Interface group mode  . . . . . . . . . . . . . . . . . .  10
     4.3.  ISIS FAD constraint sub-TLVs for automatic metric
           calculation . . . . . . . . . . . . . . . . . . . . . . .  10
       4.3.1.  Reference Bandwidth sub-TLV . . . . . . . . . . . . .  10
       4.3.2.  Threshold metric sub-TLV  . . . . . . . . . . . . . .  12
     4.4.  OSPF FAD constraint sub-TLVs for automatic metric
           calculation . . . . . . . . . . . . . . . . . . . . . . .  14
       4.4.1.  Reference Bandwidth sub-TLV . . . . . . . . . . . . .  14
       4.4.2.  Threshold metric sub-TLV  . . . . . . . . . . . . . .  16
   5.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  17
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  IGP Metric-Type Registry  . . . . . . . . . . . . . . . .  17
     7.2.  ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
           TLV . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.3.  OSPF Sub-TLVs for Flexible Algorithm Definition Sub-TLV .  18
     7.4.  Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 . . . . .  18
     7.5.  Sub-sub-TLV Codepoints for Application-Specific Link
           Attributes  . . . . . . . . . . . . . . . . . . . . . . .  18
     7.6.  OSPFv2 Extended Link TLV Sub-TLVs . . . . . . . . . . . .  19
     7.7.  Types for sub-TLVs of TE Link TLV (Value 2) . . . . . . .  19
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  19

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   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     10.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   High bandwidth traffic such as residential internet traffic and
   machine to machine elephant flows benefit from using high capacily
   links for the traffic.  Many network operators define link metric
   relative to the link capacity.  It may be useful to exclude the high
   bandwidth traffic from utilizing links below certain capacity.  A
   flex-algo [I-D.ietf-lsr-flex-algo] is defined as a set of parameters
   consisting of calculation-type, metric-type and a set of constraints.
   It is very convenient to define a flex-algo that uses bandwidth based
   metric-type which can be used for carrying high bandwidth traffic.In
   this regard, it's useful to define additional metric-type and
   additional bandwidth related constraints to simplify the operations.

   This document specifies a new metric-type to be used in flex-algo
   described in section Section 2.  Additional Flexible Algorithm
   Definition (FAD) constraints defined in section Section 3.  Section 4
   defines mechanisms to automatically calculate metric based on
   reference bandwidth and actual link bandwidth.

2.  Bandwidth Metric adevertisement

   ISIS and OSPF advertise link metric in their respective link
   information.  Multiple types of metric are supported, IGP cost, te-
   metric defined in [RFC5305] and [RFC3630] and delay metric defined in
   [RFC8570] and [RFC7471].  A brownfield network might have deployed
   legacy transport mechanisms using igp-cost and te-metric which
   continue to run during migration period.  In this brownfield network
   if the operator wants to introduce two Flex-Algos, one for delay
   metric and another for bandwidth metric, a new metric-type to carry
   bandwidth related metric, would be needed.  The IGP cost and te-
   metric may be already used by legacy applications and may not be
   available to carry link bandwidth based metric.  This document
   defines a new metric called bandwidth metric.  ISIS and OSPF will
   advertise this new type of metric in their link information.  This
   document also defines a new metric-type called "bandwidth metric" in
   the FAD sub-TLV.

2.1.  ISIS Bandwidth Metric sub-TLV

   The ISIS Bandwidth Metric sub-TLV specifies the link metric based on
   link bandwidth.  Typically, this metric is assigned by a network

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   administrator.  The bandwidth metric sub-TLV is advertised in below
   TLVs

   TLV-22 (Extended IS reachability) [RFC5305]

   TLV-222 (MT-ISN) [RFC5120]

   TLV-23 (IS Neighbor Attribute) [RFC5311]

   TLV-223 (MT IS Neighbor Attribute) [RFC5311]

   TLV-141 (inter-AS reachability information) [RFC5316]

          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                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         value                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Type  :   TBD (To be assigned by IANA)
         Length: 5 octets
         Value : metric value range (1 - 4,261,412,864)

                  Figure 1: ISIS bandwidth metric sub-TLV

   The bandwidth metric sub-TLV MUST be advertised only once.  If there
   are multiple bandwidth metric sub-TLVs in one or more received
   LSPDUs, the first one MUST be used and the subsequesnt ones MUST be
   ignored.

2.2.  OSPF Bandwidth Metric sub-TLV

   The Bandwidth Metric sub-TLV specifies the link metric based on link
   bandwidth.  Typically, this metric is assigned by a network
   administrator.  The bandwidth metric sub-TLV is a sub-TLV of the OSPF
   Link TLV and advertised in OSPF extended Link LSA [RFC7684].  The
   Bandwidth Metric sub-TLV is TLV type TBD (IANA), and is four octets
   in length.

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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            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Value...                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type  :   TBD (To be assigned by IANA)
       Length: 4 octets
       Value : metric value (1- 4,294,967,296)

                  Figure 2: OSPF bandwidth metric sub-TLV

   The bandwidth metric sub-TLV MUST be advertised only once.  If there
   are multiple bandwidth metric sub-TLVs in a receieved Link TLV, the
   first one MUST be used and the subsequent ones MUST be ignored.

3.  FAD constraint sub-TLVs

   It is useful to exclude Links having capacity lower than a minimum
   value from the flex-algo topology that is designed to carry high
   bandwidth traffic.  This can be achieved by associating link affinity
   to the lower capacity links and advertise exclude link constraint in
   the FAD for that link affinity.  This works well where the link
   capacity is constant.  When a L3 link is collection of L2 links (LAG/
   L2 Bundle) , the link bandwidth varies based on the constituent link
   going up and down.  The operator has to constantly monitor the link
   capacity and assign appropriate link affinity on link capacity
   changes beyond minimum value.  In certain cases, the minimum link
   bandwidth required may change based on the applications that use the
   high bandwidth Flex-Algo.  This document proposes a new exclude
   minimum bandwidth constraint.  When this constraint is advertised in
   a FAD, based on the advertised link bandwidth, the link will be
   pruned from the flex-algo topology if its below the FAD advertised
   Minimum bandwidth value.

   Similarly, exclude maximum link delay constraint is also defined in
   this document.  Links may have the link delay measured dynamically
   and advertised in delay metric in IGP.  For usecases that deploy low
   latency flex-algo, may want to exclude links that have delay more
   than a defined threshold.

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3.1.  ISIS FAD constraint sub-TLVs

3.1.1.  ISIS Exclude Minimum Bandwidth sub-TLV

   ISIS Flex-algo Exclude Minimum Bandwidth sub-TLV (FAEMB) is a sub-TLV
   of the ISIS 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     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Min bandwidth                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      where:

         Type: 1

         Length:  4 octets.

         Min Bandwidth:  link bandwidth is encoded in 32 bits in IEEE
      floating point format.  The units are bytes per second.

                       Figure 3: ISIS FAEMB sub-TLV

   The FAEMB sub-TLV MUST appear only once in the FAD sub-TLV.  If it
   appears more than once, the ISIS FAD Sub-TLV MUST be ignored by the
   receiver.  The total link bandwidth as advertised by the sub-TLV 9 of
   the TLV 22/222/23/223/141 is compared against the Min bandwidth
   advertised in FAEMB sub-TLV.  If the link bandwidth is lower, the
   link is excluded from the Flex-algo topology of the corresponding
   Flex-algo which advertised the FAEMB sub-TLV.  If a link does not
   have the link bandwidth advertised but the FAD contains this sub-TLV,
   then that link MUST be excluded from the topology.

3.1.2.  ISIS Exclude Maximum Delay sub-TLV

   ISIS Flex-algo Exclude Maximum Delay sub-TLV (FAEMD) is a sub-TLV of
   the ISIS FAD sub-TLV.  It 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     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     max link delay          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      where:

         Type: TBD

         Length: 3 octets

         Max link delay:  Maximum link delay in microseconds

                       Figure 4: ISIS FAEMD sub-TLV

   The FAEMD sub-TLV MUST appear only once in the FAD sub-TLV.  If it
   appears more than once, the ISIS FAD Sub-TLV MUST be ignored by the
   receiver.  The link delay [RFC8570].as advertised by the sub-TLV 33
   of the TLV 22/222/23/223/141 is compared against the Max link delay
   advertised in FAEMD sub-TLV.  If the link delay value is higher, the
   link is excluded from the Flex-algo topology of the corresponding
   Flex-algo which advertised the FAEMD sub-TLV.  If a link does not
   have the link delay advertised but the FAD contains this sub-TLV,
   then that link MUST be excluded from the topology.

3.2.  OSPF FAD constraint sub-TLVs

3.2.1.  OSPF Exclude Minimum Bandwidth sub-TLV

   OSPF Flex-algo Bandwidth Exclusion sub-TLV (FAEMB) is a sub-TLV of
   the OSPF FAD TLV.  It 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                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Min bandwidth                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      where:

         Type: TBD

         Length:  4 octets.

         Min Bandwidth:  link bandwidth is encoded in 32 bits in IEEE
      floating point format.  The units are bytes per second.

                       Figure 5: OSPF FAEMB sub-TLV

   The FAEMB sub-TLV MUST appear only once in the FAD sub-TLV.  If it
   appears more than once, the OSPF FAD TLV MUST be ignored by the
   receiver.  The total link bandwidth as advertised by the sub-TLV 6 of
   the Extended Link TLV of Extended Link Opaque LSA [RFC 7684] is
   compared against the Min bandwidth advertised in FAEMB sub-TLV.  If
   the link bandwidth is lesser, the link is excluded from the Flex-algo
   topology of the corresponding Flex-algo which advertised the FAEMB
   sub-TLV.  If a link does not have the link bandwidth advertised but
   the FAD contains this sub-TLV, then that link MUST be excluded from
   the topology.

3.2.2.  OSPF Exclude Maximum Delay sub-TLV

   OSPF Flex-algo Exclude Maximum Delay sub-TLV (FAEMD) is a sub-TLV of
   the OSPF FAD TLV.  It 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                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     max link delay                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      where:

         Type: TBD

         Length:  4 octets

         Max link delay:  Maximum link delay in microseconds

                       Figure 6: OSPF FAEMD sub-TLV

   The FAEMD sub-TLV MUST appear only once in the OSPF FAD TLV.  If it
   appears more than once, the OSPF FAD TLV MUST be ignored by the
   receiver.  The link delay as advertised by the sub-TLV 27 of the
   Extended Link TLV of Extended link opaque LSA [RFC 7684] is compared
   against the Max delay advertised in FAEMD sub-TLV.  If the link delay
   value is higher, the link is excluded from the Flex-algo topology of
   the corresponding Flex-algo which advertised the FAEMD sub-TLV.  If a
   link does not have the link delay advertised but the FAD contains
   this sub-TLV, then that link MUST be excluded from the topology.

4.  Automatic metric calculation

   Networks which are designed to be highly regular and follow uniform
   metric assignment may want to further simplify the operations by
   automatically calculating the metric based on the reference bandwidth
   or a staircase metric assignment based on bandwidth thresholds.
   Based on the advertised rules, every node automatically calculates
   the link metric of the links in the network before running SPF
   algorithm.  Based on the delay in receiving the link bandwidth
   changes, there may be possibility of micro-loops which is no
   different from IGP susceptibility to micro-loops during metric
   change.  The micro-loop avoidance procedures described in
   [I-D.bashandy-rtgwg-segment-routing-uloop] can be used to avoid
   micro-loops when the automatic metric calculation is deployed.

4.1.  Simple mode

   In simple mode, the link bandwidth of a single Layer 3 link is used.
   Two ways of automatic metric calculation is supported.

      1.  Based on reference bandwidth

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      2.  Staircase metric values based on bandwidth thresholds

4.2.  Interface group mode

   Simple mode of metric calculation may not work well when there are
   multiple parallel layer 3 interfaces between two nodes.

           A------B======C=======D
                  |              |
                   ------E-------

                       Figure 7: Parallel interfaces

   In the above diagram, there are two parallel links between B->C and
   C->D.  Lets assume the link bandwidth is uniform 10Gbps on all links.
   When Simple mode of metric derivation is used,the metric is derived
   as 10 on all links.  Traffic will be load balanced beween B-> C->D
   and B->E->D.  Since the bandwidth is higher B->C->D path, the
   requirement is t be able to assign smaller metric based on cumulative
   metric for the parallel links.

   In the interface group mode, every node identifies the set of
   parallel links betweena pair of nodes based on IGP link
   advertisements and considers cumulative bandwidth of the parallel
   links while arriving at the metric for the link.  Two ways of
   automatic metric calculation is supported for interface group mode as
   well.

      1.  Based on reference bandwidth

      2.  Staircase metric values based on bandwidth thresholds

   The cumulative metric of the parallel link is used and based on
   reference bandwidth or staircase metric assignment method, metric
   value is derived.  The derived metric is assigned to each of the
   parallel link between nodes.  Interface group mode is useful for
   deployments that do not use L2 bundles.

4.3.  ISIS FAD constraint sub-TLVs for automatic metric calculation

4.3.1.  Reference Bandwidth sub-TLV

   The Flexible Algorithm Definition Reference Bandwidth Sub-TLV (FADRB
   Sub-TLV) is a Sub-TLV of the ISIS FAD sub-TLV.  It 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     |    Reserved   |S|   Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Reference Bandwidth                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Roundoff BW.                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      Type: TBD

      Length: 10 octets.
      Reference Bandwidth: link bandwidth is encoded in 32 bits in IEEE
                           floating point format.  The units are bytes per second.
       Roundoff BW: link bandwidth is encoded in 32 bits in IEEE
                    floating point format.  The units are bytes per second.

   Flags:

                 0 1 2 3 4 5 6 7
                +-+-+-+-+-+-+-+-+
                |S| | |          |
                +-+-+-+-+-+-+-+-+

         S-flag: when set, interface group Mode MUST be used to derive total link bandwidth.

         Metric calculation: (Reference_bandwidth) /
                              (Total_link_bandwidth -
                              (Mod of(Total_link_bandwidth,roundoff_bw)))

         Round-off BW value is used to make sure the the metric
         does not change when there is smaller
         change in the link bandwidth.

                       Figure 8: ISIS FADRB sub-TLV

   The ISIS FADRB Sub-TLV MUST NOT appear more then once in an ISIS FAD
   sub-TLV.  If it appears more then once, the ISIS FAD sub-TLV MUST be
   ignored by the receiver.

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4.3.2.  Threshold metric sub-TLV

   The Flexible Algorithm Definition Threshold Bandwidth Sub-TLV (FADTB
   Sub-TLV) is a Sub-TLV of the ISIS FAD sub-TLV.  It 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     |    Reserved   |S|   Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth 1 Min.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth 1 Max.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Threshold metric 1                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  .....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth n Min.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth n Max.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Threshold metric n                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      Type: TBD

      Length: 2 + n*12 octets.Here n is equal to Number of Threshold Bandwidth sets specified.

      Flags:

                 0 1 2 3 4 5 6 7
                +-+-+-+-+-+-+-+-+
                |S| | |         |
                +-+-+-+-+-+-+-+-+

         S-flag: when set, interface group Mode MUST be used to derive total link bandwidth.

         Staircase bandwidth threshold and associated metric values.
         Threshold Bandwidth 1 Min.: Minimum link bandwidth is encoded in 32 bits in IEEE
                           floating point format.  The units are bytes per second.
         Threshold Bandwidth 1 Max.:Maximum link bandwidth is encoded in 32 bits in IEEE
                           floating point format.  The units are bytes per second.
         Threshold metric 1 : metric value range (1 - 4,294,967,296)

              When the computed link bandwidth is in the range specified by
              Min and Max threshold bandwidth values,
              the corresponding metric value is assigned to the link during SPF calculation.

                       Figure 9: ISIS FADTB sub-TLV

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   The ISIS FADTB Sub-TLV MUST NOT appear more then once in an ISIS FAD
   sub-TLV.  If it appears more then once, the ISIS FAD sub-TLV MUST be
   ignored by the receiver.

4.4.  OSPF FAD constraint sub-TLVs for automatic metric calculation

4.4.1.  Reference Bandwidth sub-TLV

   The Flexible Algorithm Definition Reference Bandwidth Sub-TLV (FADRB
   Sub-TLV) is a Sub-TLV of the OSPF FAD TLV.  It 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                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |S|   Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Reference Bandwidth                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Roundoff BW.                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      Type: TBD

      Length: 10 octets.
      Reference Bandwidth: link bandwidth is encoded in 32 bits in IEEE
                           floating point format.  The units are bytes per second.
       Roundoff BW: link bandwidth is encoded in 32 bits in IEEE
                    floating point format.  The units are bytes per second.

   Flags:

                 0 1 2 3 4 5 6 7
                +-+-+-+-+-+-+-+-+
                |S| | |         |
                +-+-+-+-+-+-+-+-+

         S-flag: when set, interface group Mode MUST be used
                 to derive total link bandwidth.

          Metric calculation: (Reference_bandwidth) /
                              (Total_link_bandwidth -
                              (Mod of(Total_link_bandwidth,roundoff_bw)))

         Round-off BW value is used to make sure the the
         metric does not change when there is smaller
         change in the link bandwidth.

                       Figure 10: OSPF FADRB sub-TLV

   The OSPF FADRB Sub-TLV MUST NOT appear more then once in an OSPF FAD
   TLV.  If it appears more then once, the OSPF FAD TLV MUST be ignored
   by the receiver.

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4.4.2.  Threshold metric sub-TLV

   The Flexible Algorithm Definition Threshold Bandwidth Sub-TLV (FADTB
   Sub-TLV) is a Sub-TLV of the OSPF FAD 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                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |S|   Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth 1 Min.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth 1 Max.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Threshold metric 1                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  .....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth n Min.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Threshold Bandwidth n Max.                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Threshold metric n                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      Type: TBD

      Length: 2 + n*12 octets.Here n is equal to Number of Threshold Bandwidth specified.

      Flags:

                 0 1 2 3 4 5 6 7
                +-+-+-+-+-+-+-+-+
                |S| | |         |
                +-+-+-+-+-+-+-+-+

         S-flag: when set, interface group Mode MUST be used to derive total link bandwidth.

         Stircase bandwidth threshold and associated metric values.
         Threshold Bandwidth 1 Min.: Minimum link bandwidth is encoded in 32 bits in IEEE
                           floating point format.  The units are bytes per second.

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         Threshold Bandwidth 1 Max.:Maximum link bandwidth is encoded in 32 bits in IEEE
                           floating point format.  The units are bytes per second.
         Threshold metric 1 : metric value range (1 - 4,294,967,296)

              When the computed link bandwidth is in the range specified by
              Min and Max threshold bandwidth values,
              the corresponding metric value is assigned to the link during SPF calculation.

                       Figure 11: OSPF FADTB sub-TLV

   The OSPF FADTB Sub-TLV MUST NOT appear more then once in an OSPF FAD
   TLV.  If it appears more then once, the OSPF FAD TLV MUST be ignored
   by the receiver.

5.  Backward Compatibility

6.  Security Considerations

   TBD

7.  IANA Considerations

7.1.  IGP Metric-Type Registry

   Type: Suggested 3 (TBA)

   Description: Bandwidth metric

   Reference: This document

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

   Type: Suggested 6 (TBA)

   Description: ISIS Exclude Minimum Bandwidth sub-TLV

   Reference: This document Section 3.1.1

   Type: Suggested 7 (TBA)

   Description: ISIS Exclude Maximum Delay sub-TLV

   Reference: This document Section 3.1.2

   Type: Suggested 8 (TBA)

   Description: ISIS Reference Bandwidth sub-TLV

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   Reference: This document Section 4.3.1

   Type: Suggested 9 (TBA)

   Description: ISIS Threshold metric sub-TLV

   Reference: This document Section 4.3.2

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

   Type: Suggested 6 (TBA)

   Description: OSPF Exclude Minimum Bandwidth sub-TLV

   Reference: This document Section 3.2.1

   Type: Suggested 7 (TBA)

   Description: OSPF Exclude Maximum Delay sub-TLV

   Reference: This document Section 3.2.2

   Type: Suggested 8 (TBA)

   Description: OSPF Reference Bandwidth sub-TLV

   Reference: This document Section 4.4.1

   Type: Suggested 9 (TBA)

   Description: OSPF Threshold metric sub-TLV

   Reference: This document Section 4.4.2

7.4.  Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223

   Type: Suggested 45 (TBA)

   Description: Bandwidth metric

   Reference: This document Section 2.1

7.5.  Sub-sub-TLV Codepoints for Application-Specific Link Attributes

   Type: Suggested 45 (TBA)

   Description: Bandwidth metric

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   Reference: This document Section 2.1

7.6.  OSPFv2 Extended Link TLV Sub-TLVs

   Type: Suggested 45 (TBA)

   Description: Bandwidth metric

   Reference: This document Section 2.2

7.7.  Types for sub-TLVs of TE Link TLV (Value 2)

   Type: Suggested 45 (TBA)

   Description: Bandwidth metric

   Reference: This document Section 2.2

8.  Acknowledgements

   Many thanks to Chris Bowers, Krzysztof Szarcowitz, Julian Lucek, Ram
   Santhanakrishnan for discussions and inputs.

9.  Contributors

   1.  Salih K A

   Juniper Networks

   salih@juniper.net

10.  References

10.1.  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>.

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   [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>.

   [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>.

10.2.  Informative References

   [I-D.bashandy-rtgwg-segment-routing-uloop]
              Bashandy, A., Filsfils, C., Litkowski, S., Decraene, B.,
              Francois, P., and P. Psenak, "Loop avoidance using Segment
              Routing", draft-bashandy-rtgwg-segment-routing-uloop-10
              (work in progress), December 2020.

   [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>.

   [RFC5311]  McPherson, D., Ed., Ginsberg, L., Previdi, S., and M.
              Shand, "Simplified Extension of Link State PDU (LSP) Space
              for IS-IS", RFC 5311, DOI 10.17487/RFC5311, February 2009,
              <https://www.rfc-editor.org/info/rfc5311>.

   [RFC5316]  Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
              December 2008, <https://www.rfc-editor.org/info/rfc5316>.

   [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>.

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Authors' Addresses

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

   Email: shraddha@juniper.net

   William Britto A J
   Juniper Networks Inc.

   Email: bwilliam@juniper.net

   Rajesh Shetty
   Juniper Networks Inc.

   Email: mrajesh@juniper.net

   Bruno Decraene
   Orange

   Email: bruno.decraene@orange.com

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