Native IPv4 multicast in IPv6 Core using PIM
draft-venaas-pim-ipv4-in-ipv6-core-00

PIM Working Group                                              S. Venaas
Internet-Draft                                                 M. Mishra
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: 29 August 2026                                       S. Buraiky
                                                                  Aramco
                                                        25 February 2026

              Native IPv4 multicast in IPv6 Core using PIM
                 draft-venaas-pim-ipv4-in-ipv6-core-00

Abstract

   This document describes how PIM Sparse-Mode can be used to construct
   IPv4 multicast trees across an IPv6-only network core.  It specifies
   the use of IPv6 PIM messages to carry IPv4 group and source
   addresses, the use of RPF vectors for reachability, and a new Hello
   Option to signal support for this capability.

Status of This Memo

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   This Internet-Draft will expire on 29 August 2026.

Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Protocol Operation  . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  PIM Message Encoding  . . . . . . . . . . . . . . . . . .   3
     3.2.  RPF Handling  . . . . . . . . . . . . . . . . . . . . . .   3
     3.3.  PIM Hello Option  . . . . . . . . . . . . . . . . . . . .   3
     3.4.  Register and Assert Messages  . . . . . . . . . . . . . .   3
     3.5.  Data Plane Requirements . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In typical network deployments, it is preferred that the network core
   remains simple, pushing complexity to the edge.  One such case
   involves providing a mix of IPv4 and IPv6 unicast and multicast at
   the edge while deploying only one address family (IPv6) in the core.

   For unicast, [RFC5549] allows building a RIB with IPv4 prefixes that
   have IPv6 next-hops, removing the requirement for IPv4 addresses on
   core routers.  This allows native IPv4 unicast packets to be
   forwarded through a network without IPv4 addresses.

   This document describes how to build IPv4 multicast trees and
   construct IPv4 multicast forwarding tables to allow native IPv4
   multicast through a network without IPv4 addresses, using PIM Sparse-
   Mode [RFC7761].

2.  Terminology

   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.

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3.  Protocol Operation

3.1.  PIM Message Encoding

   [RFC7761] uses an encoding for all IP addresses that specifies the
   address family.  This allows a PIM message with an IPv6 header to
   contain IPv4 addresses.  This document proposes exchanging PIM Join/
   Prune messages with IPv6 headers and IPv6 target addresses, where the
   Source or Group addresses within the message may be IPv4.

   It is assumed that all sources in a group record are of the same
   address family as the group itself.

3.2.  RPF Handling

   Each PIM router must determine the RPF neighbor and interface for a
   given (*,G) or (S,G).

   1.  If core routers have a RIB with IPv4 prefixes and IPv6 next-hops
       (e.g., via [RFC5549]), this information is used for the RPF
       lookup.

   2.  Alternatively, the RPF Vector [RFC5496] can be used.  This allows
       an egress core router to include RPF vector(s) with the IPv6
       address(es) of the ingress core routers in the PIM Join message.
       By doing so, the core network does not require IPv4 unicast
       routing information.

3.3.  PIM Hello Option

   To ensure interoperability, a new PIM Hello Option is probably
   needed.  A router would include this option to indicate that it
   accepts PIM messages with IPv6 headers containing IPv4 source and
   group addresses.

3.4.  Register and Assert Messages

   It is assumed that Rendezvous Points (RPs) are located outside of the
   core; therefore, no special handling for PIM Register messages is
   defined in this document.

   PIM Assert messages MUST use an IPv6 header and contain IPv4 source
   and group information.  If an RPF vector is used, it MUST be used for
   the metric calculation as specified in Section 3.3.3 of [RFC5496].

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3.5.  Data Plane Requirements

   An IPv6 core router must be able to detect native IPv4 packets
   received on the (S,G) incoming interface (for switching to the
   Shortest Path Tree) and on Outgoing Interface Lists (OIFs) for Assert
   handling.

4.  Security Considerations

   This document does not change the security properties of [RFC7761].
   However, it introduces the handling of mixed-address-family control
   packets which implementations must validate to prevent malformed
   packet processing.

5.  IANA Considerations

   If we decide to use a hello option, IANA will be requested to assign
   a new PIM Hello Option type from the "PIM Hello Options" registry for
   the option described in this document.

6.  Normative References

   [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/rfc/rfc2119>.

   [RFC5496]  Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
              Forwarding (RPF) Vector TLV", RFC 5496,
              DOI 10.17487/RFC5496, March 2009,
              <https://www.rfc-editor.org/rfc/rfc5496>.

   [RFC5549]  Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
              Layer Reachability Information with an IPv6 Next Hop",
              RFC 5549, DOI 10.17487/RFC5549, May 2009,
              <https://www.rfc-editor.org/rfc/rfc5549>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/rfc/rfc7761>.

   [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/rfc/rfc8174>.

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Authors' Addresses

   Stig Venaas
   Cisco Systems, Inc.
   Tasman Drive
   San Jose,  CA 95134
   United States of America
   Email: svenaas@cisco.com

   Mankamana Mishra
   Cisco Systems, Inc.
   821 Alder Drive
   Milpitas,  CA 95035
   United States
   Email: mankamis@cisco.com

   Salah M. Buraiky
   Aramco
   Email: salah.buraiky.1@aramco.com

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