Advertising IPv4 Network Layer Reachability Information (NLRI) with an IPv6 Next Hop
RFC 8950

Document Type RFC - Proposed Standard (November 2020; No errata)
Obsoletes RFC 5549
Authors Stephane Litkowski  , Swadesh Agrawal  , krishnaswamy ananthamurthy  , Keyur Patel 
Last updated 2020-11-19
Replaces draft-litkowski-bess-rfc5549revision
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IESG IESG state RFC 8950 (Proposed Standard)
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Internet Engineering Task Force (IETF)                      S. Litkowski
Request for Comments: 8950                                    S. Agrawal
Obsoletes: 5549                                         K. Ananthamurthy
Category: Standards Track                                          Cisco
ISSN: 2070-1721                                                 K. Patel
                                                                  Arrcus
                                                           November 2020

 Advertising IPv4 Network Layer Reachability Information (NLRI) with an
                             IPv6 Next Hop

Abstract

   Multiprotocol BGP (MP-BGP) specifies that the set of usable next-hop
   address families is determined by the Address Family Identifier (AFI)
   and the Subsequent Address Family Identifier (SAFI).  The 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 the
   advertising of 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 to determine which of the protocols the
   address actually belongs to, and a BGP Capability allowing MP-BGP
   peers to dynamically discover whether they can exchange IPv4 NLRI and
   VPN-IPv4 NLRI with an IPv6 next hop.  This document obsoletes RFC
   5549.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8950.

Copyright Notice

   Copyright (c) 2020 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
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   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
     1.1.  Requirements Language
   2.  Changes Compared to RFC 5549
   3.  Extension of AFI/SAFI Definitions for the IPv4 Address Family
   4.  Use of BGP Capability Advertisement
   5.  Operations
   6.  Usage Examples
     6.1.  IPv4 over IPv6 Core
     6.2.  IPv4 VPN Unicast over IPv6 Core
     6.3.  IPv4 VPN Multicast over IPv6 Core
   7.  IANA Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   Multiprotocol BGP (MP-BGP) [RFC4760] specifies that the set of
   network-layer protocols to which the address carried in the Next Hop
   Address field may belong is determined by the Address Family
   Identifier (AFI) and the Subsequent Address Family Identifier (SAFI).
   A number of existing AFIs/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
   [RFC6074]) to perform Layer 2 Virtual Private Network (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 Address field contains the loopback address of a
   PE.  Similarly, the AFI/SAFI <1/132> (defined in [RFC4684]) to
   advertise Route Target (RT) membership information allows advertising
   NLRI that contains such RT membership information, while the Next Hop
   Address field contains the address of the advertising router.

   Furthermore, a number of these existing AFIs/SAFIs allow the next hop
   to belong to either the IPv4 protocol or the IPv6 protocol and
   specify the encoding of the next-hop information to determine which
   of the protocols the address actually belongs to.  For example,
   [RFC4684] allows the next-hop address to be either an IPv4 or IPv6
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