SRv6 Midpoint Protection
draft-chen-rtgwg-srv6-midpoint-protection-12

Network Working Group                                            H. Chen
Internet-Draft                                             China Telecom
Intended status: Experimental                                      Z. Hu
Expires: 13 February 2024                            Huawei Technologies
                                                                 H. Chen
                                                               Futurewei
                                                                 X. Geng
                                                     Huawei Technologies
                                                                  Y. Liu
                                                            China Mobile
                                                               G. Mishra
                                                            Verizon Inc.
                                                          12 August 2023

                        SRv6 Midpoint Protection
              draft-chen-rtgwg-srv6-midpoint-protection-12

Abstract

   The current local repair mechanism, e.g., TI-LFA, allows local repair
   actions on the direct neighbors of the failed node or link to
   temporarily route traffic to the destination.  This mechanism does
   not work properly for SRv6 TE path after the failure happens in the
   destination point and IGP converges on the failure.  This document
   defines midpoint protection for SRv6 TE path, which enables other
   nodes on the network to perform endpoint behaviors for the faulty
   node, update the IPv6 destination address to the next endpoint after
   the faulty node, 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 [RFC2119] [RFC8174]
   when, and only when, they appear in all capitals, as shown here.

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/.

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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 13 February 2024.

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   document authors.  All rights reserved.

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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.  Endpoint Node as Repair Node  . . . . . . . . . . . . . .   5
     4.2.  Endpoint x Node as Repair Node  . . . . . . . . . . . . .   5
   5.  Determining whether the Endpoint could Be Bypassed  . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The current local repair mechanism, e.g., Topology-Independent Loop-
   Free Alternate (TI-LFA) ([I-D.ietf-rtgwg-segment-routing-ti-lfa]),
   allows local repair actions on the direct neighbors of the failed
   node or link to temporarily route traffic to the destination.  This
   mechanism does not work properly after the failure happens in the
   destination point and IGP converges on the failure.

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   In SRv6 TE, the IPv6 destination address (DA) in the outer IPv6
   header could be the segment endpoint of the TE path rather than the
   destination of the TE path ([RFC8986]).  After the endpoint fails and
   IGP converges, the packet with the failed endpoint as DA will be
   dropped since there is no route to this endpoint.  The direct
   neighbors of the failed endpoint will not receive the packet.
   [I-D.ietf-spring-segment-protection-sr-te-paths] and
   [I-D.hu-spring-segment-routing-proxy-forwarding] propose midpoint
   protection for SR-MPLS TE path after IGP converges on the failure of
   a node along the path.

   This document defines midpoint protection for SRv6 TE path after IGP
   converges on the failure of an endpoint on the path, which enables
   other nodes on the network to perform endpoint behaviors for the
   faulty node, update the IPv6 destination address to the next endpoint
   after the faulty node along the path, 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.  Only endpoint node can process SRH, Therefore, only
   endpoint nodes can perform midpoint protection.  There are two stages
   or time periods after an endpoint node fails.  The first is the time
   period from the failure until the IGP converges on the failure.  The
   second is the time period after the IGP converges on the failure.

   During the first time period, the packet will be sent to the direct
   neighbor of the failed endpoint node.  After detecting the failure of
   its interface to the failed endpoint node, the neighbor forwards the
   packets around the failed endpoint node.  It changes the IPv6
   destination address with the IPv6 address of the next endpoint node
   (or the last or other reasonable endpoint node) which could avoid
   going through the failed endpoint.

   During the second time period.  There is no route to the failed
   endpoint node after the IGP converges.  When a previous hop node of
   the failed endpoint node finds out that there is no route to the IPv6
   destination address (of the failed endpoint node), it changes the
   IPv6 destination address with the IPv6 address of the next endpoint
   node.  Note that the previous hop node may not be the direct neighbor
   of the failed endpoint node.

3.  SRv6 Midpoint Protection Example

   The topology 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 network for 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, suppose that Node N1 is an ingress node of
   SRv6 TE path going through N3 and N4.  Node N1 steers a packet into a
   segment list < B:2, 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:

   During the first time period (i.e., before the IGP converges), node
   N2 (direct neighbor of N3) as a Repair Node forwards the packets
   around the failed endpoint N3 after detecting the failure of the
   outbound interface to the endpoint B:3.  It changes 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 repair 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, B:6> as a repair path.

   During the second time period (i.e., after the IGP converges), node
   N2 does not have any route to the failed endpoint N3 in its FIB.
   Node N2, as a Repair Node, forwards the packets around the failed
   endpoint N3 to the next endpoint node (e.g., N4) directly.  There is
   no need to check whether the failed endpoint node is directly
   connected to N2.  N2 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.

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4.  SRv6 Midpoint Protection Behavior

   A node N protecting the failure of an endpoint node on a SRv6 path
   may be one of the following types:

   *  a transit node: The transit node cannot process SRH.  Therefore,
      only Ti-LFA can be executed on the transit node, but not midpoint
      protection.

   *  an endpoint node: the destination address (DA) of the packet
      received by N is a N's local END SID.

   *  an endpoint x node (i.e., an endpoint with cross-connect node):
      the destination address (DA) of the packet received by N is a N's
      local End.X SID with an array of layer 3 adjacencies.

   This section describes the behavior of each of these nodes as a
   repair node for the two time periods after the endpoint node fails.

4.1.  Endpoint Node as Repair 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.

     IF the primary outbound interface used to forward the packet failed
       the normal Ti-LFA is executed;
     ELSE IF there is no FIB entry for forwarding the packet THEN
       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;

4.2.  Endpoint x Node as Repair Node

   When the Repair Node is an endpoint x node, it provides fast
   protections for the failure through executing the following procedure
   after updating DA.

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       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
           the normal Ti-LFA is executed;
         ELSE IF there is no FIB entry for forwarding the packet THEN
           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;

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
   enable 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.  References

8.1.  Normative References

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   [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>.

   [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>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

8.2.  Informative References

   [I-D.hu-spring-segment-routing-proxy-forwarding]
              Hu, Z., Chen, H., Yao, J., Bowers, C., Zhu, Y., and Y.
              Liu, "SR-TE Path Midpoint Restoration", Work in Progress,
              Internet-Draft, draft-hu-spring-segment-routing-proxy-
              forwarding-23, 21 February 2023,
              <https://datatracker.ietf.org/doc/html/draft-hu-spring-
              segment-routing-proxy-forwarding-23>.

   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Litkowski, S., Bashandy, A., Filsfils, C., Francois, P.,
              Decraene, B., and D. Voyer, "Topology Independent Fast
              Reroute using Segment Routing", Work in Progress,
              Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
              11, 30 June 2023, <https://datatracker.ietf.org/doc/html/
              draft-ietf-rtgwg-segment-routing-ti-lfa-11>.

   [I-D.ietf-spring-segment-protection-sr-te-paths]
              Hegde, S., Bowers, C., Litkowski, S., Xu, X., and F. Xu,
              "Segment Protection for SR-TE Paths", Work in Progress,
              Internet-Draft, draft-ietf-spring-segment-protection-sr-
              te-paths-04, 10 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              segment-protection-sr-te-paths-04>.

   [I-D.li-rtgwg-enhanced-ti-lfa]
              Li, C., Hu, Z., Zhu, Y., and S. Hegde, "Enhanced Topology
              Independent Loop-free Alternate Fast Re-route", Work in
              Progress, Internet-Draft, draft-li-rtgwg-enhanced-ti-lfa-
              08, 4 May 2023, <https://datatracker.ietf.org/doc/html/
              draft-li-rtgwg-enhanced-ti-lfa-08>.

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Acknowledgments

   The authors would like to thank Bruno Decraene, Jeff Tantsura, Ketan
   Talaulikar and Parag Kaneriya for their comments to this work.

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,
   United States of America
   Email: Huaimo.chen@futurewei.com

   Xuesong Geng
   Huawei Technologies
   Email: gengxuesong@huawei.com

   Yisong Liu
   China Mobile
   Email: liuyisong@chinamobile.com

   Gyan S. Mishra
   Verizon Inc.
   13101 Columbia Pike
   Silver Spring,  MD 20904
   United States of America
   Phone: 301 502-1347

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   Email: gyan.s.mishra@verizon.com

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