BGP SR Policy Extensions for Virtual Transport Network
draft-dong-idr-sr-policy-vtn-01

Document Type Active Internet-Draft (individual)
Authors Jie Dong  , Zhibo Hu , Ran Pang 
Last updated 2021-07-11
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IDR Working Group                                                J. Dong
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                     Huawei Technologies
Expires: January 12, 2022                                        R. Pang
                                                            China Unicom
                                                           July 11, 2021

         BGP SR Policy Extensions for Virtual Transport Network
                    draft-dong-idr-sr-policy-vtn-01

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.  In scenarios where multiple Virtual Transport Networks
   (VTNs) exist in the network, the VTN in which the SR policy is
   instantiated may also need to be specified, so that the header of the
   packet can also be augmented with the information associated with the
   VTN.  An SR Policy candidate path can be distributed using BGP SR
   Policy.  This document defines extensions to BGP SR policy to specify
   the VTN associated with the SR policy.

Status of This Memo

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   This Internet-Draft will expire on January 12, 2022.

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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Specification of Requirements . . . . . . . . . . . . . . . .   3
   3.  VTN Information Encoding in SR Policy . . . . . . . . . . . .   3
   4.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The concept of Segment Routing (SR) policy is defined in
   [I-D.ietf-spring-segment-routing-policy].  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
   [I-D.ietf-idr-segment-routing-te-policy].

   The concept of Virtual Transport Network (VTN) is introduced in
   [I-D.ietf-teas-enhanced-vpn].  A VTN is a virtual underlay network
   which has customized network topology and a set of dedicated or
   shared network resources.  In a network, different VTNs may be
   created to meet different service requirements, and different
   services can be mapped to different VTNs.

   In scenarios where multiple virtual networks (VTNs) exist in the
   network, the identifier of VTN in which the SR policy is instantiated
   may also need to be specified, so that the header of data packet can
   also be augmented with the information of the associated VTN.  This
   document defines the BGP extensions to specify the VTN ID associated
   with a candidate path of SR policy.

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2.  Specification of Requirements

   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].

3.  VTN Information Encoding in SR Policy

   In order to specify the VTN the candidate path of SR policy is
   associated with, a new sub-TLV called "VTN sub-TLV" is defined in the
   BGP Tunnel Encapsulation Attribute [I-D.ietf-idr-tunnel-encaps].  The
   VTN sub-TLV can be carried in the BGP Tunnel Encapsulation Attribute
   with the tunnel type set to SR Policy.

   The VTN sub-TLV is optional and MUST NOT appear more than once for
   one SR Policy candidate path.  If the VTN sub-TLV appears more than
   once, the associated BGP SR Policy NLRI is considered malformed and
   the "treat-as-withdraw" strategy of [RFC7606] is applied.

   The VTN 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    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         VTN ID (4 octets)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                           Figure 1. VTN Sub-TLV

   where:

   o  Type: 123

   o  Length: 6

   o  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.

   o  RESERVED: 1 octet of reserved bits.  All of the reserved bits
      SHOULD be set to zero on transmission and MUST be ignored on
      receipt.

   o  VTN ID: A 32-bit global significant identifier which is used to
      identify a VTN.  Value 0 and 0xFFFFFFFF are reserved.

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

            SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
            Attributes:
               Tunnel Encaps Attribute (23)
                  Tunnel Type: SR Policy
                      Binding SID
                      Preference
                      Priority
                      Policy Name
                      Explicit NULL Label Policy (ENLP)
                      VTN
                      Segment List
                          Weight
                          Segment
                          Segment
                          ...
                      ...

4.  Procedures

   When a candidate path of SR policy is associated with a specific VTN,
   the originating node of SR policy SHOULD include the associated VTN
   in the BGP Tunnel Encapsulation Attribute of the BGP SR policy.  The
   setting of other fields and attributes in BGP SR policy SHOULD
   follows the mechanism as defined in
   [I-D.ietf-idr-segment-routing-te-policy].

   When a BGP speaker receives an SR Policy which is acceptable and
   usable according to the rules as defined in
   [I-D.ietf-idr-segment-routing-te-policy], and the SR Policy candidate
   path selected as the best candidate path is associated with a VTN,
   the receiver node of the SR policy SHOULD encapsulate VTN-specific
   information to the header of packets steered to the SR policy.  For
   SR Policy with IPv6 data plane, the possible approach is to
   encapsulate the VTN-ID to the packet using the mechanism defined in
   [I-D.dong-6man-enhanced-vpn-vtn-id].  For SR Policy with MPLS data
   plane, the usage of the VTN information is similar, the possible
   mechanism to encapsulate the VTN-ID to the packet is defined in
   [I-D.li-mpls-enhanced-vpn-vtn-id]

   Although the proposed mechanism allows that different candidate paths
   in one SR policy be associated with different VTNs, in normal network
   scenarios it is considered that the mapping between service to VTN is
   consistent, in such case all candidate paths of one SR policy are
   associated with the same VTN.

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5.  Security Considerations

   The security considerations of BGP and BGP SR policy apply to this
   document.

6.  IANA Considerations

   IANA has assigned the sub-TLV type as defined in Section 3 from "BGP
   Tunnel Encapsulation Attribute sub-TLVs" registry.

              Value     Description                     Reference
              ----------------------------------------------------
               123        VTN                         This document

7.  Acknowledgments

   The authors would like to thank Guoqi Xu, Lei Bao and Haibo Wang for
   the review and discussion of this document.

8.  References

8.1.  Normative References

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
              Rosen, E., Jain, D., and S. Lin, "Advertising Segment
              Routing Policies in BGP", draft-ietf-idr-segment-routing-
              te-policy-11 (work in progress), November 2020.

   [I-D.ietf-idr-tunnel-encaps]
              Patel, K., Velde, G. V. D., Sangli, S. R., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", draft-ietf-idr-
              tunnel-encaps-22 (work in progress), January 2021.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-11 (work in progress),
              April 2021.

   [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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   [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>.

8.2.  Informative References

   [I-D.dong-6man-enhanced-vpn-vtn-id]
              Dong, J., Li, Z., Xie, C., and C. Ma, "Carrying Virtual
              Transport Network Identifier in IPv6 Extension Header",
              draft-dong-6man-enhanced-vpn-vtn-id-03 (work in progress),
              February 2021.

   [I-D.ietf-teas-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Network (VPN+)
              Services", draft-ietf-teas-enhanced-vpn-07 (work in
              progress), February 2021.

   [I-D.li-mpls-enhanced-vpn-vtn-id]
              Li, Z. and J. Dong, "Carrying Virtual Transport Network
              Identifier in MPLS Packet", draft-li-mpls-enhanced-vpn-
              vtn-id-00 (work in progress), February 2021.

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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