BGP Flowspec for Computing-Aware Traffic Steering
draft-lin-idr-cats-flowspec-ts-05

IDR                                                              C. Lin
Internet Draft                                     New H3C Technologies
Intended status: Standards Track                                 H. Yao
Expires: January 08, 2027                                  China Mobile
                                                                  Z. Li
                                                           China Mobile
                                                               Q. Xiong
                                                        ZTE Corporation
                                                           July 6, 2026

             BGP Flowspec for Computing-Aware Traffic Steering
                     draft-lin-idr-cats-flowspec-ts-05

Abstract

A BGP Flow Specification is an n-tuple consisting of several matching
criteria that can be applied to IP traffic. Computing-Aware Traffic
Steering (CATS) is a framework which optimizes traffic steering to a
given service instance by taking into account the dynamic nature of
both computing and network resources. This document specifies a new BGP
Flow Spec Component Type in order to support CATS traffic forwarding.

Status of this Memo

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   This Internet-Draft will expire on 08 January 2027.

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   carefully, as they describe your rights and restrictions with
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Table of Contents

   1. Introduction...................................................2
   2. Requirements Language..........................................3
   3. Terminology....................................................3
   4. Flow Specifications for CATS...................................3
      4.1. Scenario 1................................................4
      4.2. Scenario 2................................................5
      4.3. Scenario 3................................................6
   5. Extend of BGP-FS...............................................7
      5.1. Match by CS-ID                           ...............................................7
      5.2. MARK CS-ID Action ............................................9
      5.3. Redirect to CSCI-ID  Action                                     ...................................10
   6. Error Handling................................................11
   7. Security Considerations.......................................11
   8. IANA Considerations...........................................11
      8.1. FSv2 Component types.....................................11
      8.2. CATS Action..............................................11
   9. References....................................................12
      9.1. Normative References.....................................12
      9.2. Informative References...................................12
   Authors' Addresses...............................................13

1. Introduction

   A Flow Specification (Flow Spec) is an n-tuple consisting of several
   matching criteria that can be applied to IP traffic [RFC8955].  The
   Flow Spec conveys match conditions (each may include several
   components) which are encoded using MP_REACH_NLRI and
   MP_UNREACH_NLRI attributes [RFC4760], while the associated actions
   such as redirect and traffic marking are encoded in BGP Extended
   Communities [RFC4360][RFC5701].  The IPv4 NLRI component types and
   traffic filtering actions sub-types are described in [RFC8955],
   while the IPv6 related are described in [RFC8956]. [I-D.ietf-idr-
   flowspec-v2] specifies BGP Flow Specification Version 2.[draft-ietf-
   idr-fsv2-ip-basic] defines FSv2 Extended Community Actions in the IP
   Basic TLV.

   Computing-Aware Traffic Steering (CATS) is introduced in [I-D.ietf-
   cats-framework]. The CS-ID is a globally unique object in the
   network, which can be a server's IP address, an SR label, or a
   simple unsigned numerical value. In CATS network, the C-PS component

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   performs path selection based on the CS-ID and forwards service
   traffic according to the selected path.

   This document specifies a new BGP Flow Spec Component Type to
   support CATS traffic filtering. Traffic is classified and mapped to
   the corresponding CS-ID using BGP Flow Spec rules, and path
   selection is then performed based on the CS-ID. BGP Flow Spec
   implements functions similar to the C-TC component.

   On the other hand, BGP Flow Spec can also use CS-ID as a filtering
   criterion. For the matched traffic, it forwards based on the actions
   specified by BGP Flow Spec, replacing the path selection function of
   C-PS. It also specifies traffic filtering actions to enable the
   creation of the CS-ID in the outer tunnel encapsulation when matched
   to the corresponding Flow Spec rules.

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 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when,
   they appear in all capitals, as shown here.

3. Terminology

   This document makes use of the terms as defined in [I-D. draft-ietf-
   cats-framework].

   Flow Spec: Flow Specification

   BGP-FS: Border Gateway Protocol (BGP) Flow Specification (FS)

4. Flow Specifications for CATS

   The Flow Spec for CATS is shown in Figure 1, the CATS system
   consists of a controller, a CATS  ingress node and multiple CATS
   egress nodes. CATS Framework Workflow is referenced in [I-D.ietf-
   cats-framework]. This service scheduling supports both distributed
   mode and centralized mode.

   In the distributed mode, clients send service request data
   encapsulated with a service type identifier for differentiated
   service classification. The CATS ingress node looks up registered
   information matching the service type identifier from the computing
   service topology table, and selects the optimal CATS egress node.
   Afterwards, the ingress node encapsulates the service request data,
   and forwards the encapsulated traffic to the selected egress node.

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                             +------------------+
                      /------|   Controller     |-----\              CS-ID 1
                     /       +------------------+      \             CSCI-ID 1
   +------+         FS                                 FS            +------+
   |Client|-\      /                                    \          /-|Server|
   +------+  \  +-/------+  +----------------------+  +--\-----+  /  +------+
              \-|Ingress |  |                      |  |Egress  |-/
                |CATS-FWD|--|     CATS Network     |--|CATS-FWD|      CS-ID 1
              /-|        |  |                      |  |        |-\    CSCI-ID 2
   +------+  /  +--------+  +----------------------+  +--------+  \  +------+
   |Client|-/                                                      \-|Server|
   +------+                                                          +------+
                          Figure 1. Flow Spec for CATS

   In centralized mode, the controller establishes BGP peering sessions with policy
   enforcement points within the CATS domain. Upon receiving a BGP policy, the CATS
   ingress node determines the forwarding path directly according to the embedded
   forwarding policy, or generates an updated forwarding policy combined with service
   types to obtain the final forwarding path. This document describes the main
   applications of BGP-FS in the CATS framework as follows:

4.1. Scenario 1

   Flow entries are directly pushed to redirect traffic to the CSCI-ID based on flow
   characteristics, enabling subsequent forwarding.

   Rule  1

   Filter: Flow characteristics

   Action: Redirect to IPv4/IPv6 CSCI-ID

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         +------------+
         |  BGP FS    |
         | Controller |
         +------------+
            | FlowSpec route to Ingress NLRI:
            |    Rule Condition: IP Extended Filter(Match Port, etc)
            |    Action : Redirect to IPv4/IPv6 CSCI-ID
            |
            |          .-----.
            |         (       )                   +------+
            V     .--(         )--.              -|Server|
      +-------+  (                 )  +-------+ / +------+
      |       |_(  CATS Network     )_|       |-
      |Ingress| ( ================> ) |Egress |-
      +-------+  (                )   +-------+ \ +------+
                  '--(         )--'              -|Server|
                      (       )                   +------+
                       '-----'

                        Figure 2: Scenario 1 Examples

4.2. Scenario 2

   The data layer of the traffic includes a CS-ID field. Rules are pushed to filter
   based on the CS-ID, redirecting traffic to the CSCI-ID for forwarding.

   Rule  1

   Filter: IPv4/IPv6 CS-ID

   Action: Redirect to IPv4/IPv6 CSCI-ID

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         +------------+
         |  BGP FS    |
         | Controller |
         +------------+
            | FlowSpec route to Ingress NLRI:
            |    Rule Condition: IP Extended Filter(IPv4/IPv6 CS-ID)
            |    Action : Redirect to IPv4/IPv6 CSCI-ID
            |
            |          .-----.
            |         (       )                   +------+
            V     .--(         )--.              -|Server|
      +-------+  (                 )  +-------+ / +------+
      |       |_(  CATS Network     )_|       |-
      |Ingress| ( ================> ) |Egress |-
      +-------+  (                )   +-------+ \ +------+
                  '--(         )--'              -|Server|
                      (       )                   +------+
                       '-----'

                        Figure 3: Scenario 2 Examples

4.3. Scenario 3

   Flow characteristics mapped to the CS-ID; deploy rules to filter based on the CS-
   ID and redirect traffic to the CSCI-ID for forwarding..

   Rule  1

   Filter: Flow characteristics

   Action: Mark IPv4/IPv6 CS-ID

   Rule 2

   Filter: IPv4/IPv6 CS-ID

   Action: Redirect to IPv4/IPv6 CSCI-ID

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         +------------+
         |  BGP FS    |
         | Controller |
         +------------+
            | FlowSpec route to Ingress NLRI:
            |    Rule Condition: IP Extended Filter(Match Port, etc)
            |    Action 1: Mark IPv4/IPv6 CS-ID
            |    Action 2: Redirect to IPv4/IPv6 CSCI-ID
            |
            |          .-----.
            |         (       )                   +------+
            V     .--(         )--.              -|Server|
      +-------+  (                 )  +-------+ / +------+
      |       |_(  CATS Network     )_|       |-
      |Ingress| ( ================> ) |Egress |-
      +-------+  (                )   +-------+ \ +------+
                  '--(         )--'              -|Server|
                      (       )                   +------+
                       '-----'

                        Figure 4: Scenario 3 Examples

5. Extend of BGP-FS

   This document elaborates on the protocol enhancements grounded in
   the BGP Flowspec v2 format[I-D.ietf-idr-flowspec-v2]. It introduces
   one matching: matching CS-ID. Furthermore, it enriches the action
   repertoire with two actions: Mark CS-ID action, and Redirect to
   CSCI-ID action.

   In scenario 4.1, the Redirect to CS-ID action is leveraged.

   In scenario 4.2, matching CS-ID is deployed in tandem with the
   Redirect to CS-ID action.

   In scenario 4.3, the Mark CS-ID action is implemented in conjunction
   with the Redirect to CS-ID action.

5.1. Match by CS-ID

   The format of the FSv2 NLRI field for IP Filters is defined in [I-
   D.draft-ietf-idr-flowspec-v2]. This format includes a common header
   with fields for user specified order, dependency filter chain, and a
   TLV for filter components (type, length, value).

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   This document proposes a new Component for defining CS-ID
   information from the Extended IP Filters Components for for IP
   Extended Filters version 2.

   When filtering using FlowSpec rules, the condition can be specified
   as the CS-ID.

   This is primarily used to achieve the C-PS function of CATS based on
   CS-ID for path selection.

   The IPv4 CS-ID Components has following format:

       +-------------------------------+
       |  SubTLV type = TBD1 (1 octet) |
       +-------------------------------+
       |  length (1 octet)             |
       + ------------------------------+
       |  value (variable)             |
       +-------------------------------+

   Filter defines: a list of match criteria for IPv4 CS-ID

   Type: TBD1

   length: variable

   IPv4 value: [numeric_op, value]+

   Each IPv4 CS-ID value is 4 octets.

   The IPv6 CS-ID Components has following format:

       +-------------------------------+
       |  SubTLV type = TBD2 (1 octet) |
       +-------------------------------+
       |  length (1 octet)             |
       + ------------------------------+
       |  value (variable)             |
       +-------------------------------+

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   Filter defines: a list of match criteria for IPv6 CS-ID

   Type: TBD2

   length: variable

   IPv6 value: [numeric_op, value]+

   Each IPv6 CS-ID value is 16 octets.

5.2. MARK CS-ID Action

   When implementing the C-TC function, the corresponding CS-ID is
   assigned based on traffic characteristics, which are specified
   according to the FSv2 IP Extend Filters.

   If a rule is matched, execute the Mark CS-ID action.

   This document defines a new traffic filtering action: "Mark CS-ID"
   Action. It is specifically encapsulated and carried through the BGP
   Community Container Attribute (also known as BGP Wide Communities)
   defined in [I-D.ietf-idr-wide-bgp-communities].

   "Mark IPv4 CS-ID" Action SubTLV has the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Action type(TBD3)             |   Length(4)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          IPv4 CS-ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Figure 5: "Mark IPv4 CS-ID" Action SubTLV

   "Mark IPv6 CS-ID" Action SubTLV has the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Action type(TBD4)             |   Length(16)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                          IPv6  CS-ID                          |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                            Figure 6: "Mark IPv6 CS-ID" Action SubTLV

5.3. Redirect to CSCI-ID  Action

   While specifying the path, C-PS designates the CSCI-ID information.

   "Redirect to IPv4 CSCI-ID" Action SubTLV has the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Action type(TBD5)             |   Length(4)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             CSCI-ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 7: "Redirect to IPv4 CSCI-ID" Action SubTLV

   "Redirect to IPv6 CSCI-ID" Action SubTLV has the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Action type(TBD6)             |   Length(16)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                        IPv6  CSCI-ID                          |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 8: "Redirect to IPv6 CSCI-ID" Action SubTLV

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6. Error Handling

   The error handling and validation of BGP FSv2 follows section 4 of
   [I-D.ietf-idr-flowspec-v2].  When the Mark CS-ID Action and Redirect
   to CSCI-ID Action SubTLVs are missing at the same time, the FlowSpec
   steering falls back to the FSv2 IP Basic actions in [I-D.ietf-idr-
   fsv2-ip-basic].

7. Security Considerations

   Security considerations for BGP FSv2 are covered in the [draft-ietf-
   idr-fsv2-ip-basic].The security of CATS information distributed has
   been discussed in [draft-ietf-cats-framework]. They are also
   applicable to the extensions described in this document.

8. IANA Considerations

   8.1. FSv2 Component types

   This document requested to assign new type code point from FSv2
   Component types for CS-ID.

   Table 3 Non-IP Types for IP Filters[I-D.ietf-idr-flowspec-v2]

      SubTLV

      -type     Definition

      ======    ============

      TBD1 -    CATS Match 1: IPv4 CS-ID

      TBD2 -    CATS Match 1: IPv6 CS-ID

   8.2. CATS Action

   IANA is requested to assign the following code points from the "BGP
   FSv2 Action types" Registry:

   TBD3: MARK IPv4 CS-ID Action

   TBD4: MARK IPv6 CS-ID Action

   TBD5: Redirect to IPv4 CSCI-ID Action

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   TBD6: Redirect to IPv6 CSCI-ID Action

9. References

   9.1. Normative References

   [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
             Communities Attribute", RFC 4360, DOI
             10.17487/RFC4360, February 2006, <https://www.rfc-
             editor.org/info/rfc4360>.

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

   [RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community
             Attribute", RFC 5701, DOI 10.17487/RFC5701, November
             2009, <https://www.rfc-editor.org/info/rfc5701>.

   [I-D.ietf-idr-flowspec-v2]Hares, S., Eastlake, D. E., Yadlapalli,
             C., and S. Maduschke, "BGP Flow Specification Version 2",
             Work in Progress, Internet-Draft, draft-ietf-idr-flowspec-
             v2-04, 28 April 2024,
             <https://datatracker.ietf.org/doc/html/draft-ietf-idr-
             flowspec-v2-04>.

   9.2. Informative References

   [I-D.ietf-cats-framework] C. Li.,Z. Du.,M. Boucadair.,L. M.
             Contreras., J. Drake., " A Framework for Computing-Aware
             Traffic Steering (CATS)", draft-ietf-cats-framework-
             10(work in progress), June 2025.

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Authors' Addresses

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com

   Huijuan Yao
   China Mobile
   No.32 XuanWuMen West Street
   Beijing
   100053
   China
   Email: yaohuijuan@chinamobile.com

   Zhenqiang Li
   China Mobile
   China
   Email: lizhenqiang@chinamobile.com

   Quan Xiong
   ZTE Corporation
   Email: xiong.quan@zte.com.cn

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