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Versions: 00 01 02 03 04 05                                             
Network Working Group                                            H. Chen
Internet-Draft                                             China Telecom
Intended status: Experimental                                      Z. Hu
Expires: December 17, 2021                           Huawei Technologies
                                                                 H. Chen
                                                               Futurewei
                                                                 X. Geng
                                                     Huawei Technologies
                                                           June 15, 2021


                        SRv6 Midpoint Protection
              draft-chen-rtgwg-srv6-midpoint-protection-04

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 December 17, 2021.

Copyright Notice

   Copyright (c) 2021 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  . . . . . . . . . . . . . .   6
     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  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     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 ([RFC8986]).



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   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.  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, the packet of a SRv6 TE path may not
   be sent to the direct neighbor of the failed endpoint node.  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: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:5:6> as a repair path.

   During the second time period (i.e., after the IGP converges), node
   N1 does not have any route to the failed endpoint N3 in its FIB.
   Node N1, 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 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




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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:

   o  a transit node: the destination address (DA) of the packet
      received by N is not N's local SID.

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

   o  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.  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 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 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;

    *: SL could be decreased by any dedicated value from [1-N],
    where N is the current value of SL.







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4.2.  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
       IF NH = SRH && SL != 0 and
          the failed endpoint is directly connected to 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 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;

4.3.  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
           IF NH = SRH && SL != 0 and
              the failed endpoint directly connected to 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 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
   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.




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8.  Acknowledgements

9.  References

9.1.  Normative References

   [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-14
              (work in progress), April 2021.

   [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-02 (work in progress), February
              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>.

   [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>.

   [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>.

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.hu-spring-segment-routing-proxy-forwarding]
              Hu, Z., Chen, H., Yao, J., Bowers, C., Yongqing, and
              Yisong, "SR-TE Path Midpoint Restoration", draft-hu-
              spring-segment-routing-proxy-forwarding-14 (work in
              progress), April 2021.




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   [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", draft-ietf-rtgwg-segment-
              routing-ti-lfa-06 (work in progress), February 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.

   [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", draft-li-
              rtgwg-enhanced-ti-lfa-03 (work in progress), October 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





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   Huaimo Chen
   Futurewei
   Boston, MA
   USA

   Email: Huaimo.chen@futurewei.com


   Xuesong Geng
   Huawei Technologies

   Email: gengxuesong@huawei.com







































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