BGP SR Policy Extensions for Network Resource Partition
draft-ietf-idr-sr-policy-nrp-04

IDR Working Group                                                J. Dong
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                     Huawei Technologies
Expires: 16 April 2026                                           R. Pang
                                                            China Unicom
                                                         13 October 2025

        BGP SR Policy Extensions for Network Resource Partition
                    draft-ietf-idr-sr-policy-nrp-04

Abstract

   Segment Routing (SR) Policy is a set of candidate paths, each
   consisting of one or more segment lists and the associated
   information.  The header of a packet steered in an SR Policy is
   augmented with an ordered list of segments associated with that SR
   Policy.  A Network Resource Partition (NRP) is a subset of network
   resources allocated in the underlay network which can be used to
   support one or a group of RFC 9543 network slice services.

   In networks where there are multiple NRPs, an SR Policy may be
   associated with a particular NRP.  The association between SR Policy
   and NRP needs to be specified, so that for service traffic which is
   steered into the SR Policy, the header of the packets can be
   augmented with the information associated with the NRP.  An SR Policy
   candidate path can be distributed using BGP SR Policy.  This document
   defines the extensions to BGP SR policy to specify the NRP which the
   SR Policy candidate path is associated with.

Status of This Memo

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   This Internet-Draft will expire on 16 April 2026.

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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  NRP Identifier of SR Policy . . . . . . . . . . . . . . . . .   3
   3.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Scalability Considerations  . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The concept of Segment Routing (SR) policy is defined in [RFC9256].
   An SR Policy is a set of candidate paths, each consisting of one or
   more segment lists.  The head end of an SR Policy may learn multiple
   candidate paths for an SR Policy.  The header of a packet steered in
   an SR Policy is augmented with an ordered list of segments associated
   with that SR Policy.  The BGP extensions to distribute SR Policy
   candidate paths is defined in [RFC9830].

   [RFC9543] discusses the general framework, components, and interfaces
   for requesting and operating network slices using IETF technologies.
   It also introduces the concept Network Resource Partition (NRP),
   which is a subset of the resources and associated policies in the
   underlay network.  The network slices defined in [RFC9543] can be
   realized by mapping one or more connectivity constructs to an NRP.
   [RFC9732] describes the framework and the candidate component
   technologies for providing enhanced VPN services based on VPN and

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   Traffic Engineering (TE) technologies.  Enhanced VPN (VPN+) can be
   used for the realization of network slice services defined in
   [RFC9543].

   As described in [I-D.ietf-teas-nrp-scalability], one scalable data
   plane approach to support network slicing is to carry a dedicated NRP
   ID in the data packet to identify the NRP the packet belongs to, so
   that the packet can be processed and forwarded using the subset of
   network resources allocated to the NRP.

   In networks where there are multiple NRPs, an SR Policy may be
   associated with a particular NRP.  The association between SR Policy
   and NRP needs to be specified, so that for service traffic which is
   steered into the SR Policy, the header of the packets can be
   augmented with the information associated with the NRP.  The
   association between SR Policy and NRP is described in
   [I-D.jiang-spring-sr-policy-nrp].  An SR Policy candidate path can be
   distributed using BGP SR Policy.  This document defines the
   extensions to BGP SR policy to specify the NRP which the SR Policy
   candidate path is associated with.

1.1.  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
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  NRP Identifier of SR Policy

   In order to specify the NRP the candidate path of SR policy is
   associated with, a new sub-TLV called "NRP" sub-TLV is defined in the
   BGP Tunnel Encapsulation Attribute [RFC9012].  The NRP sub-TLV can be
   carried in the BGP Tunnel Encapsulation Attribute with the tunnel
   type set to SR Policy.  The use of the NRP sub-TLV in other tunnel
   types is outside the scope of this document.

   The NRP sub-TLV 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      |     Flags     |   Reserved    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         NRP ID (4 octets)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Figure 1. NRP Sub-TLV

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   where:

   *  Type: 123 (assigned by IANA)

   *  Length: 6 octets.

   *  Flags: 1-octet flag field.  None is defined at this stage.  The
      flags SHOULD be set to zero on transmission and MUST be ignored on
      receipt.

   *  Reserved: 1 octet of reserved bits.  It SHOULD be set to zero on
      transmission and MUST be ignored on receipt.

   *  NRP ID: A 32-bit domain significant identifier which is used to
      identify an NRP in the control plane.  The values of 0 and
      0xFFFFFFFF are reserved.

   The validation of an SR Policy NLRI with the NRP Sub-TLV in the BGP
   tunnel encapsulation attribute [RFC9012] follows the procedures in
   section 4.2 of [RFC9830], augmented by the validation procedures
   described in this document.

   When the NRP sub-TLV is carried in the BGP Tunnel Encapsulation
   Attribute of an SR Policy NLRI, a segment list of the candidate path
   is considered invalid if the headend node of the SR Policy determines
   that the set of network resources corresponding to the NRP ID on
   network segments identified by the segment list do not exist.  The
   detailed mechanisms for NRP resource validation are out of the scope
   of this document.

   The encoding structure of BGP SR Policy with the NRP sub-TLV is
   expressed as below:

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            SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
            Attributes:
               Tunnel Encaps Attribute (23)
                  Tunnel Type: SR Policy (15)
                      Binding SID
                      SRv6 Binding SID
                      Preference
                      Priority
                      Policy Name
                      Policy Candidate Path Name
                      Explicit NULL Label Policy (ENLP)
                      NRP
                      Segment List
                          Weight
                          Segment
                          Segment
                          ...
                      ...
                Figure 2. SR Policy Encoding with NRP sub-TLV

3.  Procedures

   When a candidate path of SR Policy is instantiated within an NRP, and
   a network-wide data plane NRP Selector ID is used for identifying the
   resources of the NRP, the originating node of SR Policy SHOULD
   include the NRP sub-TLV in the BGP Tunnel Encapsulation Attribute of
   the BGP SR Policy.  The setting of other fields and attributes in BGP
   SR Policy SHOULD follow the mechanism as defined in [RFC9830].

   On reception of an SR Policy NLRI, a BGP speaker determines if it is
   acceptable and usable according to the rules defined in Section 4.2
   of [RFC9830] and section 2 of this document.  If the SR Policy
   candidate path selected as the best candidate path is associated with
   an NRP, the headend node of the SR Policy SHOULD map the NRP ID to
   the data plane NRP Selector ID, then encapsulate both the NRP
   Selector ID and the segment list of the selected candidate path in
   the header of packets which are steered to the SR Policy.  For SR
   Policy with IPv6 data plane, the data plane NRP Selector ID can be
   the same as the NRP ID, and the approach to encapsulate the NRP
   Selector ID in IPv6 Hop-by-Hop Options header is defined in
   [I-D.ietf-6man-enhanced-vpn-vtn-id].  For SR Policy with MPLS data
   plane, the mechanisms of mapping and encapsulation of the NRP
   Selector ID in the packet would based on the framework defined in
   [RFC9789].

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   Although the proposed mechanism allows that different candidate paths
   in one SR policy be associated with different NRPs, in normal network
   scenarios it is considered that the association between an SR Policy
   and NRP is consistent, in such case all candidate paths of one SR
   policy SHOULD be associated with the same NRP.

4.  Error Handling

   The error handling of the BGP Update messages for BGP SR Policy SAFI
   with the NRP extensions defined in this document follows the
   procedures in section 5 of [RFC9830].

   The NRP sub-TLV is optional and MUST NOT appear more than once for
   one SR Policy candidate path.  The NRP sub-TLV is considered
   malformed if its format does not match the above description.  If the
   NRP sub-TLV appears more than once, or its format is considered
   malformed, the associated BGP SR Policy NLRI is considered malformed
   and the "treat-as-withdraw" strategy of [RFC7606] MUST be applied.

5.  Scalability Considerations

   The mechanism specified in this document adds additional information
   to the SR Policy candidate paths.  In order to steer traffic into
   different NRPs using SR Policy, the SR Policies used for different
   NRPs need to be different.  As the number of NRP increases, the
   number of SR Policies would also increase accordingly.  When BGP is
   used for distributing SR Policy candidate paths, the amount of
   control plane information exchanged between the network controller
   and the headend nodes would also increase.  However, since the SR
   Policies candidate paths distributed in BGP are only installed by the
   corresponding headend nodes, the impacts to the BGP control plane are
   considered acceptable.

6.  Security Considerations

   The security considerations of BGP [RFC4271] and BGP SR policy
   [RFC9830] apply to this document.

   The NRP sub-TLV provides the NRP identifier that may be carried in
   IPv6 Hop-by-Hop options header or used in the encapsulation of MPLS.
   This NRP identifier can impact packet forwarding in a network so care
   should be taken to protect this mission-critical or commercially
   sensitive information during provisioning, query and report of the
   NRP-ID in BGP.

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7.  IANA Considerations

   IANA has assigned the sub-TLV type as defined in Section 2 from "BGP
   Tunnel Encapsulation Attribute sub-TLVs" registry.

              Value     Description                     Reference
              ----------------------------------------------------
               123        NRP                         This document

8.  Acknowledgments

   The authors would like to thank Guoqi Xu, Lei Bao, Haibo Wang,
   Shunwan Zhuang and Susan Hares for their review and discussion of
   this document.

9.  References

9.1.  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>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

   [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>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.

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   [RFC9543]  Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
              Makhijani, K., Contreras, L., and J. Tantsura, "A
              Framework for Network Slices in Networks Built from IETF
              Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
              <https://www.rfc-editor.org/info/rfc9543>.

   [RFC9732]  Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for NRP-Based Enhanced Virtual Private
              Networks", RFC 9732, DOI 10.17487/RFC9732, March 2025,
              <https://www.rfc-editor.org/info/rfc9732>.

   [RFC9830]  Previdi, S., Filsfils, C., Talaulikar, K., Ed., Mattes,
              P., and D. Jain, "Advertising Segment Routing Policies in
              BGP", RFC 9830, DOI 10.17487/RFC9830, September 2025,
              <https://www.rfc-editor.org/info/rfc9830>.

9.2.  Informative References

   [I-D.ietf-6man-enhanced-vpn-vtn-id]
              Dong, J., Li, Z., Xie, C., Ma, C., and G. S. Mishra,
              "Carrying Network Resource (NR) related Information in
              IPv6 Extension Header", Work in Progress, Internet-Draft,
              draft-ietf-6man-enhanced-vpn-vtn-id-12, 7 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-6man-
              enhanced-vpn-vtn-id-12>.

   [I-D.ietf-teas-nrp-scalability]
              Dong, J., Li, Z., Gong, L., Yang, G., and G. S. Mishra,
              "Scalability Considerations for Network Resource
              Partition", Work in Progress, Internet-Draft, draft-ietf-
              teas-nrp-scalability-07, 2 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              nrp-scalability-07>.

   [I-D.jiang-spring-sr-policy-nrp]
              Yue, Chen, R., Dong, J., Lin, C., Pang, R., KaZhang, gao,
              W., and J. Wenying, "Segment Routing Policy Extension for
              Network Resource Partition", Work in Progress, Internet-
              Draft, draft-jiang-spring-sr-policy-nrp-03, 30 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-jiang-spring-
              sr-policy-nrp-03>.

   [RFC9789]  Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
              Network Actions (MNAs) Framework", RFC 9789,
              DOI 10.17487/RFC9789, July 2025,
              <https://www.rfc-editor.org/info/rfc9789>.

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Authors' Addresses

   Jie Dong
   Huawei Technologies
   Email: jie.dong@huawei.com

   Zhibo Hu
   Huawei Technologies
   Email: huzhibo@huawei.com

   Ran Pang
   China Unicom
   Email: pangran@chinaunicom.cn

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