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Network Working Group                                            H. Chen
Internet-Draft                                             China Telecom
Intended status: Experimental                                      Z. Hu
Expires: April 18, 2021                              Huawei Technologies
                                                                 H. Chen
                                                               Futurewei
                                                                 X. Geng
                                                     Huawei Technologies
                                                        October 15, 2020


                        SRv6 Midpoint Protection
              draft-chen-rtgwg-srv6-midpoint-protection-03

Abstract

   The current local repair mechanism, e.g., TI-LFA, allows local repair
   actions on the direct neighbors of the failed node to temporarily
   route traffic to the destination.  This mechanism could not work
   properly when the failure happens in the destination point or the
   link connected to the destination.  In SRv6 TE, the IPv6 destination
   address in the outer IPv6 header could be the dedicated endpoint of
   the TE path rather than the destination of the TE path.  When the
   endpoint fails, local repair couldn't work on the direct neighbor of
   the failed endpoint either.  This document defines midpoint
   protection, which enables the direct neighbor of the failed endpoint
   to do the function of the endpoint, replace the IPv6 destination
   address to the other endpoint, and choose the next hop based on the
   new destination address.

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



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   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 April 18, 2021.

Copyright Notice

   Copyright (c) 2020 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
   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.  SRv6 Midpoint Protection Mechanism  . . . . . . . . . . . . .   3
   3.  SRv6 Midpoint Protection Example  . . . . . . . . . . . . . .   3
   4.  SRv6 Midpoint Protection Behavior . . . . . . . . . . . . . .   5
     4.1.  Transit Node as Repair Node . . . . . . . . . . . . . . .   5
     4.2.  Endpoint Node as Repair Node  . . . . . . . . . . . . . .   5
     4.3.  Endpoint x Node as Repair Node  . . . . . . . . . . . . .   6
   5.  Determining whether the Endpoint could Be Bypassed  . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The current mechanism, e.g., TI-LFA
   ([I-D.ietf-rtgwg-segment-routing-ti-lfa]), allows local repair
   actions on the direct neighbors of the failed node to temporarily
   route traffic to the destination.  This mechanism could not work
   properly when the failure happens in the destination point or the
   link connected to the destination.  In SRv6 TE, the IPv6 destination
   address in the outer IPv6 header could be the dedicated endpoint of
   the TE path rather than the destination of the TE path



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   ([I-D.ietf-spring-srv6-network-programming]).  When the endpoint
   fails, local repair couldn't work on the direct neighbor of the
   failed endpoint either.  This document defines midpoint protection,
   which enables the direct neighbor of the failed endpoint to do the
   function of the endpoint, replace the IPv6 destination address to the
   other endpoint, and choose the next hop based on the new destination
   address.

2.  SRv6 Midpoint Protection Mechanism

   When an endpoint node fails, the packet needs to bypass the failed
   endpoint node and be forwarded to the next endpoint node of the
   failed endpoint.  On the Repair Node (i.e., the previous hop of the
   failed endpoint node), it performs the proxy forwarding as follows :

   o  Outbound interface failure happens in the Repair Node;

   Case 1: Route to the failed endpoint could be found in the FIB of
   Repair Node:

   o  If the Repair Node is not directly connected to the failed
      endpoint, the normal Ti-LFA is executed;

   o  If the Repair Node is directly connected to the failed endpoint,
      the Repair Node forwards the packets through a bypass to the
      failed endpoint, changing the IPv6 destination address with the
      IPv6 address of the next, the last or other reasonable endpoint
      nodes, which could avoid going throw the failed endpoint.

   Case 2: Route to the failed endpoint could not be found in the FIB of
   Repair Node:

   o  Repair Node forwards the packets through a bypass of the failed
      endpoint to the next, the last or other reasonable endpoint node
      directly . There is no need to check whether the failed endpoint
      node is directly connected to the Repair Node or not.

3.  SRv6 Midpoint Protection Example

   The topology shown in Figure 1 illustrates an example of network
   topology with SRv6 enabled on each node.










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                      +-----+           +-----+
                      |  N5 |-----------|  N6 |--------------+
                      +-----+           +-----+              |
                         |                 |                 |
                         |                 |                 |
                         |                 |                 |
    +-----+           +-----+           +-----+           +-----+
    |  N1 |-----------|  N2 |-----------|  N3 |-----------|  N4 |
    +-----+           +-----+           +-----+           +-----+


   Figure 1: An example of midpoint protection

   In this document, an end SID at node n with locator block B is
   represented as B:n.  An end.x SID at node n towards node k with
   locator block B is represented as B:n:k.  A SID list is represented
   as <S1, S2, S3> where S1 is the first SID to visit, S2 is the second
   SID to visit and S3 is the last SID to visit along the SRv6 TE path.

   In the reference topology:

   Node N1 is an ingress node of SRv6 domain.  Node N1 steers a packet
   into a segment list < B:3, B:4>.

   When Node N3 fails, the packet needs to bypass the failed endpoint
   node and be forwarded to the next endpoint node after the failed
   endpoint in the TE path.  When outbound interface failure happens in
   the Repair Node (which is not limited to the previous hop node of the
   failed endpoint node), it performs the proxy forwarding as follows,:

   For node N2, if the outbound interface to the endpoint B:3 is failed
   before IGP converges:

   o  Because node N2, as a Repair Node, is connected to the failed
      endpoint B:3 directly, node N2 forwards the packets through a
      bypass of the failed endpoint, changing the IPv6 destination
      address with the next sid B:4.  N2 detects the failure of outbound
      interface to B:4 in the current route, it could use the normal Ti-
      LFA repait path to forward the packet, because it is not directly
      connected to the node N4.  N2 encapsulates the packet with the
      segment list < B:5:6> as a repair path.

   For node N1, route to the failed endpoint N3 could not be found in
   the FIB after IGP converges:

   o  Node N1, as a Repair Node, forwards the packets through a bypass
      of the failed endpoint to the next or endpoint node (e.g., N4)
      directly.  There is no need to check whether the failed endpoint



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      node is directly connected to N1.  N1 changes the IPv6 destination
      address with the next sid B:4.  Since IGP has completed
      convergence, it forwards packets directly based on the IGP SPF
      path

4.  SRv6 Midpoint Protection Behavior

4.1.  Transit Node as Repair Node

   When the Repair Node is a transit node, it provides fast protection
   against the endpoint node failure as follows after looking up the
   FIB.

     IF the primary outbound interface used to forward the packet failed
       IF NH = SRH && SL != 0, and
          the failed endpoint is directly connected to the Repair Node THEN
         SL decreases*; update the IPv6 DA with SRH[SL];
         FIB lookup on the updated DA;
         forward the packet according to the matched entry;
       ELSE
         forward the packet according to the backup nexthop;
     ELSE // there is no FIB entry for forwarding the packet
       IF NH = SRH && SL != 0 THEN
         SL decreases*; update the IPv6 DA with SRH[SL];
         FIB lookup on the updated DA;
         forward the packet according to the matched entry;
       ELSE
         drop the packet;

*: SL could decrease any dedicated value from [1-N], where N is the current value of SL.
The case is similar in the following examples.

4.2.  Endpoint Node as Repair Node

   When a node N receives a packet, if the destination address (DA) of
   the packet is a local END SID, then node N is an endpoint node.  When
   the Repair Node is an endpoint node, it provides fast protections for
   the failure through executing the following procedure after looking
   up the FIB for the updated DA.












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     IF the primary outbound interface used to forward the packet failed
       IF NH = SRH && SL != 0, and
          the failed endpoint is directly connected to the Repair Node THEN
         SL decreases; update the IPv6 DA with SRH[SL];
         FIB lookup on the updated DA;
         forward the packet according to the matched entry;
       ELSE
         forward the packet according to the backup nexthop;
     ELSE // there is no FIB entry for forwarding the packet
       IF NH = SRH && SL != 0 THEN
         SL decreases; update the IPv6 DA with SRH[SL];
         FIB lookup on the updated DA;
         forward the packet according to the matched entry;
       ELSE
         drop the packet;
     ELSE
       forward accordingly to the matched entry;

4.3.  Endpoint x Node as Repair Node

   An endpoint node with cross-connect (End.X for short) is an endpoint
   node with an array of layer 3 adjacencies.  When a node N receives a
   packet, if the destination address (DA) of the packet is a local
   END.X SID, then node N as Repair Node provides fast protections for
   the failure through executing the following procedure after updating
   DA.

     IF the layer-3 adjacency interface is down THEN
       FIB lookup on the updated DA;
       IF the primary interface used to forward the packet failed THEN
         IF NH = SRH && SL != 0, and
            the failed endpoint directly connected to the Repair Node THEN
           SL decreases; update the IPv6 DA with SRH[SL];
           FIB lookup on the updated DA;
           forward the packet according to the matched entry;
         ELSE
           forward the packet according to the backup nexthop;
       ELSE // there is no FIB entry for forwarding the packet
         IF NH = SRH && SL != 0 THEN
           SL decreases; update the IPv6 DA with SRH[SL];
           FIB lookup on the updated DA;
           forward the packet according to the matched entry;
         ELSE
           drop the packet;
     ELSE
       forward accordingly to the matched entry;





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5.  Determining whether the Endpoint could Be Bypassed

   SRv6 Midpoint Protection provides a mechanism to bypass a failed
   endpoint.  But in some scenarios, some important functions may be
   implemented in the bypassed failed endpoints that should not be
   bypassed, such as firewall functionality or In-situ Flow Information
   Telemetry of a specified path.  Therefore, a mechanism is needed to
   indicate whether an endpoint can be bypassed or not.
   [I-D.li-rtgwg-enhanced-ti-lfa] provides method to determine whether
   enbale SRv6 midpoint protection or not by defining a "no bypass" flag
   for the SIDs in IGP.

6.  Security Considerations

   This section reviews security considerations related to SRv6 Midpoint
   protection processing discussed in this document.To ensure that the
   Repair node does not modify the SRH header Encapsulated by nodes
   outside the SRv6 Domain.Only the segment within the SRH is same
   domain as the repair node.  So it is necessary to check the skipped
   segment have same block as repair node.

7.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

8.  Acknowledgements

9.  References

9.1.  Normative References

   [I-D.hu-spring-segment-routing-proxy-forwarding]
              Hu, Z., Chen, H., Yao, J., Bowers, C., and Y. Zhu, "SR-TE
              Path Midpoint Protection", draft-hu-spring-segment-
              routing-proxy-forwarding-11 (work in progress), August
              2020.

   [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-25 (work in progress), May 2019.






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   [I-D.ietf-lsr-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extension to Support Segment Routing over
              IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11
              (work in progress), October 2020.

   [I-D.ietf-lsr-ospfv3-srv6-extensions]
              Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
              "OSPFv3 Extensions for SRv6", draft-ietf-lsr-
              ospfv3-srv6-extensions-01 (work in progress), August 2020.

   [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.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-24 (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>.

   [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.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-07 (work in progress),
              July 2020.

   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
              Francois, P., Voyer, D., Clad, F., and P. Camarillo,
              "Topology Independent Fast Reroute using Segment Routing",
              draft-ietf-rtgwg-segment-routing-ti-lfa-04 (work in
              progress), August 2020.




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   [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-08 (work in progress),
              July 2020.

   [I-D.li-rtgwg-enhanced-ti-lfa]
              Li, C. and Z. Hu, "Enhanced Topology Independent Loop-free
              Alternate Fast Re-route", draft-li-rtgwg-enhanced-ti-
              lfa-02 (work in progress), August 2020.

   [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-07 (work in progress), July 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

   Huanan Chen
   China Telecom
   109, West Zhongshan Road, Tianhe District
   Guangzhou  510000
   China

   Email: chenhuan6@chinatelecom.cn


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

   Email: huzhibo@huawei.com


   Huaimo Chen
   Futurewei
   Boston, MA
   USA

   Email: Huaimo.chen@futurewei.com



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   Xuesong Geng
   Huawei Technologies

   Email: gengxuesong@huawei.com















































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