Advertising IPv4 Network Layer Reachability Information with an IPv6 Next Hop
RFC 5549

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Network Working Group                                     F. Le Faucheur
Request for Comments: 5549                                      E. Rosen
Category: Standards Track                                  Cisco Systems
                                                                May 2009

        Advertising IPv4 Network Layer Reachability Information
                         with an IPv6 Next Hop

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   Multiprotocol BGP (MP-BGP) specifies that the set of network-layer
   protocols to which the address carried in the Next Hop field may
   belong is determined by the Address Family Identifier (AFI) and the
   Subsequent Address Family Identifier (SAFI).  The current AFI/SAFI
   definitions for the IPv4 address family only have provisions for
   advertising a Next Hop address that belongs to the IPv4 protocol when
   advertising IPv4 Network Layer Reachability Information (NLRI) or
   VPN-IPv4 NLRI.  This document specifies the extensions necessary to
   allow advertising IPv4 NLRI or VPN-IPv4 NLRI with a Next Hop address
   that belongs to the IPv6 protocol.  This comprises an extension of
   the AFI/SAFI definitions to allow the address of the Next Hop for
   IPv4 NLRI or VPN-IPv4 NLRI to also belong to the IPv6 protocol, the
   encoding of the Next Hop in order to determine which of the protocols
   the address actually belongs to, and a new BGP Capability allowing
   MP-BGP Peers to dynamically discover whether they can exchange IPv4
   NLRI and VPN-IPv4 NLRI with an IPv6 Next Hop.

Le Faucheur & Rosen         Standards Track                     [Page 1]
RFC 5549                   v4 NLRI with v6 NH                   May 2009

Table of Contents

   1. Introduction ....................................................2
   2. Requirements Language ...........................................4
   3. Extension of AFI/SAFI Definitions for the IPv4 Address Family ...4
   4. Use of BGP Capability Advertisement .............................5
   5. Operations ......................................................7
   6. Usage Examples ..................................................7
      6.1. IPv4 over IPv6 Core ........................................7
      6.2. IPv4 VPN over IPv6 Core ....................................8
   7. IANA Considerations .............................................8
   8. Security Considerations .........................................8
   9. Acknowledgments .................................................9
   10. References .....................................................9
      10.1. Normative References ......................................9
      10.2. Informative References ....................................9

1.  Introduction

   Multiprotocol BGP (MP-BGP) [RFC4760] specifies that the set of
   network-layer protocols to which the address carried in the Next Hop
   field may belong is determined by the Address Family Identifier (AFI)
   and the Subsequent Address Family Identifier (SAFI).  A number of
   existing AFI/SAFIs allow the Next Hop address to belong to a
   different address family than the Network Layer Reachability
   Information (NLRI).  For example, the AFI/SAFI <25/65> used (as per
   [L2VPN-SIG]) in order to perform L2VPN auto-discovery, allows
   advertising NLRI that contains the identifier of a Virtual Private
   LAN Service (VPLS) instance or that identifies a particular pool of
   attachment circuits at a given Provider Edge (PE), while the Next Hop
   field contains the loopback address of a PE.  Similarly, the AFI/SAFI
   <1/132> (defined in [RFC4684]) in order to advertise Route Target
   (RT) membership information, allows advertising NLRI that contains
   such RT membership information, while the Next Hop field contains the
   address of the advertising router.

   Furthermore, a number of these existing AFI/SAFIs allow the Next Hop
   to belong to either the IPv4 Network Layer Protocol or the IPv6
   Network Layer Protocol, and specify the encoding of the Next Hop
   information in order to determine which of the protocols the address
   actually belongs to.  For example, [RFC4684] allows the Next Hop