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Versions: 00

Network Working Group                                              Z. Hu
Internet-Draft                                                   H. Chen
Intended status: Standards Track                                   P. Wu
Expires: September 6, 2019                           Huawei Technologies
                                                           March 5, 2019


                      SRv6 Path Egress Protection
                draft-hu-rtgwg-srv6-egress-protection-00

Abstract

   This document describes protocol extensions and procedures for
   protecting the egress node of a Segment Routing for IPv6 (SRv6) path.

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
   working documents as Internet-Drafts.  The list of current Internet-
   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 September 6, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  SR Path Egress Protection . . . . . . . . . . . . . . . . . .   3
   4.  Extensions to IGP for Egress Protection . . . . . . . . . . .   5
     4.1.  Extensions to IS-IS . . . . . . . . . . . . . . . . . . .   5
     4.2.  Extensions to OSPF  . . . . . . . . . . . . . . . . . . .   7
   5.  Behavior for SRv6 Mirror SID  . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Fast protection of a transit node of a Segment Routing (SR) path is
   described in [I-D.bashandy-rtgwg-segment-routing-ti-lfa] and
   [I-D.hu-spring-segment-routing-proxy-forwarding].  However, these
   documents do not discuss the procedures for fast protection of the
   egress node of a Segment Routing for IPv6 (SRv6) path.

   This document fills that void and specifies protocol extensions and
   procedures for fast protection of the egress node of an SRv6 path.
   Egress node and egress as well as fast protection and protection will
   be used exchangeably.

2.  Terminologies

   The following terminologies are used in this document.

   SR:  Segment Routing

   SRv6:  SR for IPv6

   SRH:  Segment Routing Header

   SID:  Segment Identifier

   CE:  Customer Edge



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   PE:  Provider Edge

   LFA:  Loop-Free Alternate

   TI-LFA:  Topology Independent LFA

   TE:  Traffic Engineering

   BFD:  Bidirectional Forwarding Detection

   VPN:  Virtual Private Network

   L3VPN:  Layer 3 VPN

   VRF:  Virtual Routing and Forwarding

   FIB:  Forwarding Information Base

   PLR:  Point of Local Repair

   BGP:  Border Gateway Protocol

   IGP:  Interior Gateway Protocol

   OSPF:  Open Shortest Path First

   IS-IS:  Intermediate System to Intermediate System

3.  SR Path Egress Protection

   Figure 1 shows an example of protecting egress PE3 of a SR path,
   which is from ingress PE1 to egress PE3.

                                     Locator: A3:1::/64
                  *******  *******   VPN SID: A3:1::B100
              [PE1]-----[P1]-----[PE3]
              / |        |&        | \            PE3 Egress
             /  |        |&        |  \           CEx Customer Edge
        [CE1]   |        |&        |   [CE2]      Px  Non-Egress
             \  |        |&        |  /           *** SR Path
              \ |        |& &&&&&  | /            &&& Backup Path
              [PE2]-----[P2]-----[PE4]
                                     Locator: A4:1::/64
                                     VPN SID: A4:1::B100
                                  Mirror SID: A4:1::3, protect A3:1::/64

                  Figure 1: Protecting SR Path Egress PE3




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   Node P1's pre-computed TI-LFA backup path for PE3 is from P1 to PE4
   via P2.  In normal operations, after receiving a packet with
   destination PE3, P1 forwards the packet to PE3 according to its FIB.
   When PE3 receives the packet, it sends the packet to CE2.

   When PE3 fails, P1 detects the failure through BFD and forwards the
   packet to PE4 via the backup path.  When PE4 receives the packet, it
   sends the packet to the same CE2.

   In Figure 1, CE2 is dual home to PE3 and PE4.  PE3 has a locator
   A3:1::/64 and a VPN SID A3:1::B100.  PE4 has a locator A4:1::/64 and
   a VPN SID A4:1::B100.  A mirror SID A4:1::3 is configured on PE4 for
   protecting PE3 with locator A3:1::/64.

   After the mirror SID is configured on a local PE (e.g., PE4), when
   the local PE (e.g., BGP on the local PE) receives a prefix whose VPN
   SID belongs to a remote PE (e.g., PE3) with the locator that is
   protected by the local PE through mirror SID, the local PE (e.g.,
   PE4) creates a mapping from the remote PE's (e.g., PE3's) VPN SID and
   the mirror SID to the local PE's (e.g., PE4's) VPN SID.  The remote
   PE is protected by the local PE.

   For example, local PE4 has Prefix 1.1.1.1 with VPN SID:A4:1::B100,
   when PE4 receives prefix 1.1.1.1 with remote PE3's VPN SID
   A3:1::B100, it creates a mapping from remote PE3's VPN SID and the
   mirror SID (i.e., "A3:1::B100, A4:1::3") to local PE4's VPN SID
   (i.e., "A4:1::B100").

   Node P1's pre-computed TI-LFA backup path for destination PE3 having
   locator A3:1::/64 is from P1 to PE4 having mirror SID A4:1::3.  It is
   installed as a T.Insert transit behavior.  When P1 receives a packet
   destined to PE3's VPN SID A3:1::B100, in normal operations, it
   forwards the packet with source A1:1:: and destination PE3's VPN SID
   A3:1::B100 according to the FIB using the destination PE3's VPN SID
   A3:1::B100.

   When PE3 fails, node P1 protects PE3 through sending the packet to
   PE4 via the backup path pre-computed.  P1 modifies the packet before
   sending it to PE4.  The modified packet has destination PE4 with
   mirror SID A4:1::3, and SRH with PE3's VPN SID A3:1::B100 and the
   mirror SID A4:1::3 (i.e., "A3:1::B100, A4:1::3; SL=1").

   When PE4 receives the packet, it forwards the packet to CE2 through
   executing END.M instruction according to the local VPN SID (i.e.,
   A4:1::B100).






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4.  Extensions to IGP for Egress Protection

   This section describes extensions to IS-IS and OSPF for advertising
   the information about SRv6 path egress protection.

4.1.  Extensions to IS-IS

   A new sub-TLV, called IS-IS SRv6 End.m SID sub-TLV, is defined.  It
   is used in the SRv6 Locator TLV defined in
   [I-D.bashandy-isis-srv6-extensions] to advertise SRv6 Segment
   Identifiers (SIDs) with END.M function for SRv6 path egress
   protection.  The SRv6 End.m SIDs inherit the topology/algorithm from
   the parent locator.  The format of the sub-TLV is illustrated below.

     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 (TBD1)   |    Length     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Flags     |    SRv6 Endpoint Function     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SID (16 octets)                       |
    :                                                               :
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            sub-TLVs                           |
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2: IS-IS SRv6 End.m SID sub-TLV

   Type:  TBD1 (suggested value 8) is to be assigned by IANA.

   Length:  variable.

   Flags:  1 octet.  No flags are currently defined.

   SRv6 Endpoint Function:  2 octets.  Add a new endpoint function 40
      for end.m SID.

   SID:  16 octets.  This field contains the SRv6 end.m SID to be
      advertised.

   Two sub-TLVs are defined.  One is the protected locators sub-TLV, and
   the other is the protected SIDs sub-TLV.

   A protected locators sub-TLV is used to carry the Locators to be
   protected by the SRv6 mirror SID.  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 (TBD2)  |    Length     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Locator-Size  | Locator (variable)            ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Locator-Size  | Locator (variable)            ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: IS-IS Protected Locators sub-TLV

   Type:  TBD2 (suggested value 1) is to be assigned by IANA.

   Length:  variable.

   Locator-Size:  1 octet.  Number of bits (1 - 128) in the Locator
      field.

   Locator:  1-16 octets.  This field encodes an SRv6 Locator to be
      protected by the SRv6 mirror SID.  The Locator is encoded in the
      minimal number of octets for the given number of bits.

   A protected SIDs sub-TLV is used to carry the SIDs to be protected by
   the SRv6 mirror SID.  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 (TBD3)  |    Length     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SID (16 octets)                       ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SID (16 octets)                       ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 4: IS-IS Protected SIDs sub-TLV

   Type:  TBD3 (suggested value 2) is to be assigned by IANA.

   Length:  variable.

   SID:  16 octets.  This field encodes an SRv6 SID to be advertised.




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4.2.  Extensions to OSPF

   Similarly, a new sub-TLV, called OSPF SRv6 End.m SID sub-TLV, is
   defined.  It is used to advertise SRv6 Segment Identifiers (SIDs)
   with END.M function for SRv6 path egress protection.  Its format is
   illustrated below.

     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 (TBD4)           |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Flags     |    SRv6 Endpoint Function     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SID (16 octets)                       |
    :                                                               :
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            sub-TLVs                           |
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 5: OSPF SRv6 End.m SID sub-TLV

   Type:  TBD4 (suggested value 8) is to be assigned by IANA.

   Length:  variable.

   Flags:  1 octet.  No flags are currently defined.

   SRv6 Endpoint Function:  2 octets.  Add a new endpoint function 40
      for end.m SID.

   SID:  16 octets.  This field contains the SRv6 end.m SID to be
      advertised.

   Two sub-TLVs are defined.  One is the protected locators sub-TLV, and
   the other is the protected SIDs sub-TLV.

   A protected locators sub-TLV is used to carry the Locators to be
   protected by the SRv6 mirror SID.  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 (TBD5)           |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Locator-Size  |  Locator (variable)           ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Locator-Size  |  Locator (variable)           ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 6: OSPF Protected Locators sub-TLV

   Type:  TBD5 (suggested value 1) is to be assigned by IANA.

   Length:  variable.

   Locator-Size:  1 octet.  Number of bits (1 - 128) in the Locator
      field.

   Locator:  1-16 octets.  This field encodes an SRv6 Locator to be
      protected by the SRv6 mirror SID.  The Locator is encoded in the
      minimal number of octets for the given number of bits.

   A protected SIDs sub-TLV is used to carry the SIDs to be protected by
   the SRv6 mirror SID.  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 (TBD6)           |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SID (16 octets)                       ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SID (16 octets)                       ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 7: OSPF Protected SIDs sub-TLV

   Type:  TBD6 (suggested value 2) is to be assigned by IANA.

   Length:  variable.

   SID:  16 octets.  This field encodes an SRv6 SID to be advertised.




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5.  Behavior for SRv6 Mirror SID

   The "Endpoint with mirror protection to a vpn SID" function (End.M
   for short) is a variant of the End function.  The End.M is used for
   SRv6 VPN egress protection.  It is described below.

     End.M: Mirror protection
     When N receives a packet destined to S and S is a local End.M SID,
     N does:
     IF NH=SRH and SL = 1 ;; Ref1
        SL--
        Map to a local VPN SID based on Mirror SID and SRH[SL] ;; Ref1
        forward according to the local VPN SID ;; Ref2
     ELSE
      drop the packet

                    Figure 8: SRv6 Mirror SID Procedure

   Ref1:  An End.M SID must always be the penultimate SID.

   Ref2:  The rest forwarding behavior is the same as the corresponding
      VPN sid.

6.  Security Considerations

   TBD

7.  IANA Considerations

   TBD

8.  Acknowledgements

   TBD

9.  References

9.1.  Normative References

   [I-D.bashandy-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extensions to Support Routing over IPv6
              Dataplane", draft-bashandy-isis-srv6-extensions-04 (work
              in progress), October 2018.







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   [I-D.hu-spring-segment-routing-proxy-forwarding]
              Hu, Z., Chen, H., Yao, J., and C. Bowers, "Segment Routing
              Proxy Forwarding", draft-hu-spring-segment-routing-proxy-
              forwarding-01 (work in progress), March 2019.

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., and B. Decraene, "IS-IS Extensions for
              Segment Routing", draft-ietf-isis-segment-routing-
              extensions-22 (work in progress), December 2018.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-27 (work in progress), December 2018.

   [I-D.li-ospf-ospfv3-srv6-extensions]
              Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
              "OSPFv3 Extensions for SRv6", draft-li-ospf-
              ospfv3-srv6-extensions-02 (work in progress), September
              2018.

   [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>.

   [RFC7356]  Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
              Scope Link State PDUs (LSPs)", RFC 7356,
              DOI 10.17487/RFC7356, September 2014,
              <https://www.rfc-editor.org/info/rfc7356>.

9.2.  Informative References

   [I-D.bashandy-rtgwg-segment-routing-ti-lfa]
              Bashandy, A., Filsfils, C., Decraene, B., Litkowski, S.,
              Francois, P., daniel.voyer@bell.ca, d., Clad, F., and P.
              Camarillo, "Topology Independent Fast Reroute using
              Segment Routing", draft-bashandy-rtgwg-segment-routing-ti-
              lfa-05 (work in progress), October 2018.

   [I-D.hegde-spring-node-protection-for-sr-te-paths]
              Hegde, S., Bowers, C., Litkowski, S., Xu, X., and F. Xu,
              "Node Protection for SR-TE Paths", draft-hegde-spring-
              node-protection-for-sr-te-paths-04 (work in progress),
              October 2018.




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   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
              bogdanov@google.com, b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
              policy-02 (work in progress), October 2018.

   [I-D.sivabalan-pce-binding-label-sid]
              Sivabalan, S., Filsfils, C., Tantsura, J., Hardwick, J.,
              Previdi, S., and C. Li, "Carrying Binding Label/Segment-ID
              in PCE-based Networks.", draft-sivabalan-pce-binding-
              label-sid-06 (work in progress), February 2019.

   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching
              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
              Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
              2009, <https://www.rfc-editor.org/info/rfc5462>.

Authors' Addresses

   Zhibo Hu
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: huzhibo@huawei.com


   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   Email: Huaimo.chen@huawei.com


   Peng Wu
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: baggio.wupeng@huawei.com








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