Multicast-only Fast Reroute Based on Topology Independent Loop-free Alternate Fast Reroute
draft-liu-pim-mofrr-tilfa-03

Document Type Active Internet-Draft (individual)
Authors Yisong Liu  , Mike McBride  , Zheng Zhang  , Jingrong Xie 
Last updated 2021-02-20
Stream (None)
Intended RFC status (None)
Formats plain text pdf htmlized (tools) htmlized bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
PIM Working Group                                            Yisong Liu
Internet Draft                                             China Mobile
Intended status: Standards Track                             M. McBride
Expires: August 21, 2021                                      Futurewei
                                                               Z. Zhang
                                                                    ZTE
                                                                 J. Xie
                                                                 Huawei
                                                           Feb 21, 2021

    Multicast-only Fast Reroute Based on Topology Independent Loop-free
                          Alternate Fast Reroute
                       draft-liu-pim-mofrr-tilfa-03

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), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on August 21, 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
   (http://trustee.ietf.org/license-info) in effect on the date of

Liu, et al.             Expires August, 2021                  [Page 1]
Internet-Draft          MoFRR based on TILFA             February 2021

   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.

Abstract

   Multicast-only Fast Reroute (MoFRR) has been defined in [RFC7431],
   but the selection of the secondary multicast next hop only according
   to the loop-free alternate fast reroute, which has restrictions in
   multicast deployments. This document describes a mechanism for
   Multicast-only Fast Reroute by using Topology Independent Loop-free
   Alternate fast reroute, which is independent of network topology and
   can achieve covering more network environments.

Table of Contents

   1. Introduction ................................................ 2
      1.1. Requirements Language .................................. 3
      1.2. Terminology ............................................ 3
   2. Problem Statement ........................................... 3
   3. Solution .................................................... 4
      3.1. Secondary UMH Selection ................................ 5
      3.2. Extension Protocol Fields Conflict ..................... 5
   4. Packet Format ............................................... 6
   5. IANA Considerations ......................................... 7
   6. Security Consideration  ..................................... 7
   7. References .................................................. 7
      7.1. Normative References ................................... 7
      7.2. Informative References ................................. 8
   8. Acknowledgments ............................................. 8
   Authors' Addresses ............................................. 9

1. Introduction

   As the deployment of video services, operators are paying more and
   more attention to solutions that minimize the service disruption due
   to faults in the IP network carrying the packets for these services.
   Multicast-only Fast Reroute (MoFRR) has been defined in [RFC7431],
   which can minimize multicast packet loss in a network when node or
   link failures occur by making simple enhancements to multicast
   routing protocols such as Protocol Independent Multicast (PIM). But
   the selection of the secondary multicast next hop only according to
   the loop-free alternate fast reroute in [RFC7431], and there are
   limitations in multicast deployments for this mechanism. This

Liu, et al.             Expires August, 2021                  [Page 2]
Internet-Draft          MoFRR based on TILFA             February 2021

   document describes a new mechanism for Multicast-only Fast Reroute
   using Topology Independent Loop-free Alternate (TILFA) fast reroute,
   which is independent of network topology and can achieve covering
   more network environments.

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.

1.2. Terminology

   This document use the terms defined in [RFC7431], and also use the
   concepts defined in [RFC7490]. The specific content of each term is
   not described in this document.

2. Problem Statement

   In [RFC7431] section 3, the secondary Upstream Multicast Hop (UMH)
   of PIM for MoFRR is a loop-free alternate (LFA). However, the
   traditional LFA mechanism needs to satisfy at least one neighbor
   whose next hop to the destination node is an acyclic next hop,
   existing limitations in network deployments, and can only cover part
   of the network topology environments. In some network topology, the
   corresponding secondary UMH cannot be calculated, so PIM cannot
   establish a standby multicast tree and cannot implement MoFRR
   protection. Therefore, the current MoFRR of PIM is only available in
   the network topology applicable to LFA.

   The remote loop-free alternate (RLFA) defined in [RFC7490] is
   extended from the LFA and can cover more network deployment
   scenarios through the tunnel as an alternate path. The RLFA
   mechanism needs to satisfy at least one node assumed to be N in the
   network that the fault node is neither on the path from the source
   node to the N node, nor on the path from the N node to the
   destination node. RLFA only has enhancement compared to LFA but
   still has limitations in network deployments.

   [I-D.ietf-rtgwg-segment-routing-ti-lfa] defined a unicast FRR
   solution based on the TILFA mechanism. The TILFA mechanism can
   express the backup path with an explicit path, and has no constraint
   on the topology, providing a more reliable FRR mechanism. The
   unicast traffic can be forwarded according to the explicit path list
   as an alternate path to implement unicast traffic protection, and
   can achieve full coverage of various networking environments.

Liu, et al.             Expires August, 2021                  [Page 3]
Internet-Draft          MoFRR based on TILFA             February 2021

   The alternate path provided by the TILFA mechanism is actually a
   Segment List, including one or more Adjacency SIDs of one or more
   links between the P space and the Q space, and the NodeSID of P
   space node. PIM can look up the corresponding node IP   address in
   the unicast route according to the NodeSID, and the IP addresses of
   the two endpoints of the corresponding link in the   unicast route
   according to the Adjacency SIDs, but the multicast   protocol
   packets cannot be directly sent along the path of the   Segment
   List.

   PIM join message need to be sent hop-by-hop to establish a standby
   multicast tree. However, not all of the nodes and links on the
   unicast alternate path are included in the Segment List. If the PIM
   protocol packets are transmitted only in unicast mode, then
   equivalently the PIM packets are transmitted through the unicast
   tunnel like unicast traffic, and cannot pass through the
   intermediate nodes of the   tunnel. The intermediate nodes of the
   alternate path cannot forward multicast traffic because there are no
   PIM state entries on the nodes. PIM needs to create entries on the
   device hop-by-hop and generate an incoming interface and an outgoing
   interface list. So it can form an end-to-end complete multicast tree
   for forwarding multicast traffic. Therefore, it is not possible to
   send PIM packets like unicast traffic according to the Segment List
   path and can only establish a standby multicast tree.

   It is available in principle that the path information of the
   Segment List is added to the PIM packets to guide the hop-by-hop RPF
   selection. The IP address of the node corresponding to the NodeSID
   can be used as the segmented root node, and the IP addresses of the
   interfaces at both endpoints of the link corresponding to the
   Adjacency SID can be used directly as the local upstream interface
   and upstream neighbor, but there is currently no field in protocol
   packet to carry the explicit path specified by the Segment List. For
   the PIM protocol, the PIM RPF Vector attribute was defined in
   [RFC5496], which can carry the node IP address corresponding to the
   NodeSID. The Explicit RPF Vector was defined in [RFC7891], which can
   carry the peer IP address corresponding to the Adjacency SID, but if
   there are multiple same peer IP addresses corresponding to the
   Adjacency SID (i.e. anycast IP address), the upstream neighbor of
   RPF selection may be different from the actual upstream link
   corresponding to the Adjacency SID, which can make the PIM join path
   and the TILFA calculation path inconsistent.

3. Solution

   An Upstream Multicast Hop (UMH) is a candidate next-hop that can be
   used to reach the root of the tree.  In This document the secondary

Liu, et al.             Expires August, 2021                  [Page 4]
Internet-Draft          MoFRR based on TILFA             February 2021

   UMH is based on unicast routing to find Segment List calculated by
   TILFA.

   This document extends the PIM protocol, to establish the standby
   multicast tree according to the Segment List calculated by TILFA,
   and can achieve full coverage of various networking environments for
   MoFRR protection of multicast services.

   Assume that the Segment List calculated by TILFA is (NodeSID(A),
   AdjSID(A-B)). Node A belongs to the P Space, and node B belongs to
   the Q space. The IP address corresponding to NodeSID(A) can be
   looked up in the local link state database of the IGP protocol, and
   can be assumed to be IP-a. The IP addresses of the two endpoints of
   the link corresponding to AdjSID(A-B) can also be looked up in the
   local link state database of the IGP protocol, and can be assumed to
   be IP-La and IP-Lb.

3.1. Secondary UMH Selection

   In the procedure of PIM, IP-a can be looked as the normal RPF vector
   attribute and added to the PIM join packet. IP-La and IP-Lb can be
   looked as the RPF Vector attribute of the adjacency relationship,
   called Adjacency RPF Vector, which is a new type of PIM join
   attributes, and added to the PIM join packet too.

   The PIM protocol firstly can select the RPF incoming interface and
   upstream towards IP-a, and can join hop-by-hop to establish the PIM
   standby multicast tree until the node A. On the node A, IP-Lb can be
   looked as one PIM neighbor. If there are multiple PIM neighbors with
   the same address IP-Lb, all of the corresponding local interfaces on
   the node A need to be checked. The interface that is the only one
   with the IP address IP-La can be looked as the RPF incoming
   interface. The node A can send the PIM join packet to the node B on
   the interface of IP-La, and IP-Lb is used as the RPF upstream
   address of the PIM join.

   After the PIM join packet is received on the node B, the PIM
   protocol can find no more join attributes and select the RPF
   incoming interface and upstream towards the multicast source
   directly, and then can continue to join hop-by-hop to establish the
   PIM standby multicast tree until the router directly connected the
   source.

3.2. Extension Protocol Fields Conflict

   PIM Adjacency RPF Vector attribute is newly defined in join
   attributes. If there are conflicts from multiple downstream PIM
   neighbors, the mechanism in [RFC5384] Section 3.3.3 can be used to

Liu, et al.             Expires August, 2021                  [Page 5]
Internet-Draft          MoFRR based on TILFA             February 2021

   select a PIM downstream neighbor with a numerically smallest IP
   address. If at least two neighbors have the same IP address, the
   interface index MUST be used as a tie breaker.

4. Packet Format

   This section describes the format of PIM join message extension
   introduced by this document.

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Addr Family   | Encoding Type | Rsrvd   |S|W|R|  Mask Len     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Source Address
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
    |F|E| Attr_Type | Length        | Value
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
    |F|E| Attr_Type | Length        | Value
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
         .                    .                     .
         .                    .                     .

   The original PIM join attribute already has been defined in
   [RFC5384]

    Attr_Type:

    0- Vector ;

    4- Explicit RPF Vector ;

    Other existing definitions are not related to RPF Vector Attribute.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |F|E| Type      | Length        |        Value
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-.......

    The definition of Adjacency RPF Vector attribute

Liu, et al.             Expires August, 2021                  [Page 6]
Internet-Draft          MoFRR based on TILFA             February 2021

    F bit: 0, indicating that the unrecognized device does not forward
    the attribute

    E bit: indicates the last join attribute

    Type: TBD

    Length: depends on the address family of Encoded-Unicast address,
    including the length of 2 addresses.

    Value: Encoded-Unicast Address format defined in [RFC7761] Section
    4.9.1, including 2 addresses. The first one indicates the address of
    the local interface, and the second one indicates the address of the
    peer interface. Only the case of the same address family is
    supported.

5. IANA Considerations

   This document requests IANA to assign a registry for Adjacency RPF
   Vector in PIM Join Attribute and the Explicit Path TLV Node Address
   Sub TLV. The assignment is requested permanent for IANA when this
   document is published as an RFC. The string TBD should be replaced
   by the assigned values accordingly.

6. Security Considerations

   For general PIM-SM protocol Security Considerations, see [RFC7761].

   TBD

7. References

7.1. Normative References

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

   [RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol
             Independent Multicast (PIM) Join Attribute Format",
             RFC 5384, November 2008

   [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
             Forwarding (RPF) Vector TLV", RFC 5496, March 2009

   [RFC7431] Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B.
             Decraene, "Multicast-Only Fast Reroute", RFC 7431, August
             2015

Liu, et al.             Expires August, 2021                  [Page 7]
Internet-Draft          MoFRR based on TILFA             February 2021

   [RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
             So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
             RFC 7490, April 2015

   [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas,
             I.,Parekh, R., Zhang, Z., and L. Zheng, "Protocol
             IndependentMulticast - Sparse Mode (PIM-SM): Protocol
             Specification(Revised)", RFC 7761, March 2016

   [RFC7891] Asghar, J., Wijnands, IJ., Ed., Krishnaswamy, S., Karan,
             A., and V. Arya, "Explicit Reverse Path Forwarding (RPF)
             Vector", RFC 7891, June 2016

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

   [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

7.2. Informative References

   TBD

8. Acknowledgments

   The authors would like to thank the following for their valuable
   contributions of this document:

   TBD

Liu, et al.             Expires August, 2021                  [Page 8]
Internet-Draft          MoFRR based on TILFA             February 2021

Authors' Addresses

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

   Mike McBride
   Futurewei Inc.
   USA
   Email: michael.mcbride@futurewei.com

   Zheng(Sandy) Zhang
   ZTE Corporation
   China
   Email: zhang.zheng@zte.com.cn

   Jingrong Xie
   Huawei Technologies
   China
   Email: xiejingrong@huawei.com

Liu, et al.             Expires August, 2021                  [Page 9]