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Path-aware Remote Protection Framework
draft-liu-rtgwg-path-aware-remote-protection-00

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Yisong Liu , Changwang Lin , Mengxiao Chen
Last updated 2024-02-22
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draft-liu-rtgwg-path-aware-remote-protection-00
Network Working Group                                            Y. Liu
Internet Draft                                             China Mobile
Intended status: Informational                                   C. Lin
Expires: August 21, 2024                                        M. Chen
                                                   New H3C Technologies
                                                      February 23, 2024

                  Path-aware Remote Protection Framework
              draft-liu-rtgwg-path-aware-remote-protection-00

Abstract

   This document describes the framework of path-aware remote
   protection.

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
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   This Internet-Draft will expire on August 21, 2024.

Copyright Notice

   Copyright (c) 2024 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
   (http://trustee.ietf.org/license-info) in effect on the date of

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   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
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   warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. Use Case.......................................................3
      2.1. Spine-leaf Network........................................3
      2.2. Dragonfly Network.........................................4
   3. Framework......................................................5
      3.1. Path-Aware Forwarding Plane...............................5
      3.2. Path-Aware Routing Plane..................................6
      3.3. Remote Fault Detection....................................7
   4. Security Considerations........................................7
   5. IANA Considerations............................................7
   6. References.....................................................7
      6.1. Normative References......................................7
      6.2. Informational References..................................7
   Authors' Addresses................................................8

1. Introduction

   Current IP network protection mechanisms can be mainly divided into
   local protection and end-to-end protection. Local protection
   technologies, such as ECMP, LFA [RFC5714], and TI-LFA [I-D.ietf-
   rtgwg-segment-routing-ti-lfa], can only perceive local faults and
   perform fast reroute. End-to-end protection technologies are usually
   targeted at end-to-end TE paths, where the head-end detects TE path
   faults and performs rapid switchover.

   There is no mechanism to quickly detect remote faults for non-TE
   paths and invoke repairs. In addition, local protection such as TI-
   LFA technology relies on IGP deployment. For certain networks,
   current protection mechanisms may not meet the requirements. A
   typical scenario is the Spine-Leaf network, such as the AI-DC
   network, which is usually a two-layer architecture. Detecting remote
   faults and invoking fast repairs can provide protection against link
   or node failure and reduce the disruption time.

   This paper proposes a path-aware remote protection mechanism and
   describes its framework.

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1.1. Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2. Use Case

2.1. Spine-leaf Network

            +--+     +--+
     Spine  |R1|     |R2|
            +--+     +--+
             | \      /|
             |   \  /  |
             |    \/   |
             |    /\   X <- Fault
             |   /  \  |
             | /      \|
            +--+     +--+
     Leaf   |R3|     |R4|
            +--+     +--+
             ^         |
             |         v
            Source   Destination

              Figure 1

   In the network shown in Figure 1, assuming that the R2-R4 link
   fails, R3 will continue to send traffic to both R1 and R2, and half
   of the traffic will be dropped by R2. It is not until R2 sends BGP
   withdrawn routes to R3 and the control plane converges that the
   traffic is fully restored. The convergence speed would be slow when
   there is a large number of BGP routes.

   In some Spine-leaf networks, such as DC networks, only the BGP
   protocol is deployed without IGP, and thus TI-LFA cannot be applied.
   On the other hand, if TI-LFA is used, the traffic path during the
   protection period will be R3->R2->R3->R1->R4, which additionally
   increases the traffic in the direction of R2->R3 and may cause
   congestion.

   The objective of path-aware remote protection is for R3 to detect
   R2-R4 link failure and then adjust ECMP quickly.

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2.2. Dragonfly Network

        Source
          |
          v
     +---------+
     |         |
     | Group 1 |------------+
     |         |            |
     +---------+            |
          |            +---------+
          |            |         |
          X<- Fault    | Group 3 |
          |            |         |
          |            +---------+
     +---------+            |
     |         |            |
     | Group 2 |------------+
     |         |
     +---------+
          |
          v
     Destination

              Figure 2

   In the network shown in Figure 1, the primary path for the traffic
   is from Group 1 to Group 2, while the backup path detours from
   Group1 through Group3 and then to Group2.

   The objective of path-aware remote protection is for the routers in
   Group 1 to detect the link failure between Group 1 and Group 2 and
   then invoke the backup path quickly.

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3. Framework

     +-------------+
     |Routing Plane|
     +-------------+
             |
             | Path Info
             v
     +----------------+
     |Forwarding Plane|
     +----------------+
             ^
             | Element Failure in Path
             |
     +----------------------+
     |Remote Fault Detection|
     +----------------------+

           Figure 3

   The framework of path-aware remote protection is shown in Figure 3.

   On the routing plane, the route calculation is not limited to the
   next hop, but requires path awareness. And then the path information
   is downloaded to the forwarding plane. When a fault occurs in any
   component along the path, it is required to quickly detect the fault
   and invoke repairs.

3.1. Path-Aware Forwarding Plane

   Figure 4 shows the forwarding entries for ECMP next-hops. When
   detecting any failure in the path, the corresponding next-hop will
   be removed from ECMP immediately.

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     +------+       +---------------+
     |Prefix|---+-->|Next-hop: to R1|
     +------+   |   +---------------+
                |           |           +----------------+
                |           +---------->|Path: R3->R1->R4|
                |                       +----------------+
                |   +---------------+
                +-->|Next-hop: to R2|
                    +---------------+
                            |           +----------------+
                            +---------->|Path: R3->R2->R4|
                                        +----------------+

                      Figure 4

   Figure 5 shows the forwarding entries for primary and backup next-
   hops. When detecting any failure in the path related with the
   primary next-hop, the traffic next-hop will be invoked immediately.

     +------+       +-----------------------+
     |Prefix|---+-->|Primary Next-hop: to G2|
     +------+   |   +-----------------------+
                |           |           +------------+
                |           +---------->|Path: G1->R2|
                |                       +------------+
                |   +----------------------+
                +-->|Backup Next-hop: to G3|
                    +----------------------+
                            |           +----------------+
                            +---------->|Path: G1->G3->G2|
                                        +----------------+

                      Figure 5

3.2. Path-Aware Routing Plane

   When calculating routes, the path is perceived and the path
   information is added into the next hop.

   It may be achieved through routing protocol extensions. For example,
   in figure 1, when R2 advertises R4's routes to R3 through BGP, it
   carries the router-id of R4, and R3 adds R4 into the path
   information when calculating those received routes. For another
   example, IGP can easily get the path information during the SPF
   calculation.

   The detailed mechanisms will not be included in this document.

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3.3. Remote Fault Detection

   The failure of the components in the path associated with the next
   hop should be detected, and then rapid repairs are invoked.

   It may be achieved through the use of non-routing protocol
   announcements by neighbors. For example, in Figure 1, R2 can notify
   R3 of the R2-R4 failure using UDP-based protocol or Ethernet LLC.

   It may also be achieved through a traffic-based mechanism. For
   example, when the traffic packets are dropped, a notification is
   triggered and is sent to neighbors in the direction of the incoming
   traffic.

   The detailed mechanisms will not be included in this document.

4. Security Considerations

   TBD.

5. IANA Considerations

   TBD.

6. References

6.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
             2119 Key Words", BCP 14, RFC 8174, May 2017

6.2. Informational References

   [RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC
             5714, DOI 10.17487/RFC5714, January 2010,
             <https://www.rfc-editor.org/info/rfc5714>.

   [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-13 (work in
             progress), January 2024.

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Authors' Addresses

   Yisong Liu
   China Mobile
   China
   Email: liuyisong@chinamobile.com

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com

   Mengxiao Chen
   New H3C Technologies
   China
   Email: chen.mengxiao@h3c.com

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