BESS Working Group                                             G. Mishra
Internet-Draft                                              Verizon Inc.
Intended status: Standards Track                             J. Tantsura
Expires: 19 November 2022                                Microsoft, Inc.
                                                             18 May 2022


             IPv4-Only PE Design for IPv6-NLRI with IPv4-NH
                draft-mishra-bess-ipv4-only-pe-design-01

Abstract

   As Enterprises and Service Providers try to decide whether or not to
   upgrade their brown field or green field MPLS/SR core to an IPv6
   transport, Multiprotocol BGP (MP-BGP)now plays an important role in
   the transition of their Provider (P) core network as well as Provider
   Edge (PE) Edge network from IPv4 to IPv6.  Operators must be able to
   continue to support IPv4 customers when both the Core and Edge
   networks are IPv4-Only.

   This document details an important External BGP (eBGP) PE-CE Edge
   IPv4-Only peering design that leverages the MP-BGP capability
   exchange by using IPv4 peering as pure transport, allowing both IPv4
   Network Layer Reachability Information (NLRI) and IPv6 Network Layer
   Reachability Information (NLRI)to be carried over the same (Border
   Gateway Protocol) BGP TCP session.  The design change provides the
   same Dual Stacking functionality that exists today with separate IPv4
   and IPv6 BGP sessions as we have today.  With this design change from
   a control plane perspective a single IPv4 is required for both IPv4
   and IPv6 routing updates and from a data plane forwarindg perspective
   an IPv4 address need only be configured on the PE and CE interface
   for both IPv4 and IPv6 packet forwarding.

   This document provides a IPv4-Only PE design solution for use cases
   where operators are not yet ready to migrate to IPv6 or SRv6 core and
   would like to stay on IPv4-Only Core short to long term and maybe
   even indefinitely.  With this design, operators can now remain with
   an IPv4-Only Core and do not have to migrate to an IPv6-Only Core.
   From a technical standpoint the underlay can remain IPv4 and still
   transport IPv6 NLRI to support IPv6 customers, and so does not need
   to be migrated to IPv6-Only underlay.  With this IPv4-Only PE Design
   solution , IPv4 addressing only needs to be provisioned for the
   IPv4-Only PE-CE eBGP Edge peering design, thereby eliminating IPv6
   provisioning at the Edge.  This core and edge IPv4-Only peering
   design can apply to any eBGP peering, public internet or private,
   which can be either Core networks, Data Center networks, Access
   networks or can be any eBGP peering scenario.  This document provides
   vendor specific test cases for the IPv4-Only peering design as well



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   as test results for the five major vendors stakeholders in the
   routing and switching indusrty, Cisco, Juniper, Arista, Nokia and
   Huawei.  With the test results provided for the IPv4-Only Edge
   peering design, the goal is that all other vendors around the world
   that have not been tested will begin to adopt and implement this new
   Best Current Practice for eBGP IPv4-Only Edge peering.

   This Best Current Practice IPv4-only eBGP peering design
   specification will help in use cases where operators are not yet
   ready to migrate to IPv6 or SRv6 core or for very lage operator core
   with thousdands of nodes where it maybe impractical to change the
   underlay infrastructure to IPv6, and can now keep the existing IPv4
   data plane IP, MPLS or SR-MPLS underlay intact indefinitely.

   This document also defines a new IPv4 next hop encoding for IPv6 NLRI
   over IPv4 Next Hop to uses 4 byte IPv4 address for the next hop and
   not a IPv4 mapped IPv6 address.  This encoding has been adopted by
   the industry but has not been standardized until now with this
   document.

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).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on 19 November 2022.

Copyright Notice

   Copyright (c) 2022 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
   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 to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   6
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  IPv6-Only Edge Peering Architecture . . . . . . . . . . . . .   6
     4.1.  Problem Statement . . . . . . . . . . . . . . . . . . . .   7
     4.2.  IPv4-Only PE-CE Design Solution . . . . . . . . . . . . .   8
     4.3.  IPv4-Only Edge Peering Design . . . . . . . . . . . . . .   9
       4.3.1.  IPv4-Only Edge Peering Packet Walk  . . . . . . . . .   9
       4.3.2.  6to4 Softwire IPv4-Only Core packet walk  . . . . . .   9
       4.3.3.  4to6 Softwire IPv6-Only Core packet walk  . . . . . .  11
     4.4.  RFC5549 and RFC8950 Applicability to IPv4-Only PE
           Design  . . . . . . . . . . . . . . . . . . . . . . . . .  13
       4.4.1.  IPv4-Only Edge Peering design next-hop encoding . . .  14
       4.4.2.  IPv4-Only PE Design Next Hop Encoding . . . . . . . .  14
   5.  IPv4-Only PE Design Edge E2E Test Cases . . . . . . . . . . .  16
     5.1.  Test-1 E2E IPv4-Only PE-CE, Global Table over IPv4-Only
            Core(6PE), 6to4 softwire . . . . . . . . . . . . . . . .  17
     5.2.  Test-2 E2E IPv4-Only PE-CE, VPN over IPv4-Only Core, 6to4
            Softwire . . . . . . . . . . . . . . . . . . . . . . . .  17
     5.3.  Test-3 E2E IPv4-Only PE-CE, Global Table over IPv6-Only
            Core (4PE), 4to6 Softwire  . . . . . . . . . . . . . . .  18
     5.4.  Test-4 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core, 4to6
            Softwire . . . . . . . . . . . . . . . . . . . . . . . .  18
     5.5.  Test-5 E2E IPv4-Only PE-CE, Global Table over IPv4-Only
            Core(6PE), 6to4 softwire -Inter-AS Option-B  . . . . . .  19
     5.6.  Test-6 E2E IPv4-Only PE-CE, Global Table over IPv4-Only
            Core(6PE), 6to4 softwire -Inter-AS Option-C  . . . . . .  19
     5.7.  Test-7 E2E IPv4-Only PE-CE, VPN over IPv4-Only, 6to4
            softwire -Inter-AS Option-B  . . . . . . . . . . . . . .  20
     5.8.  Test-8 E2E IPv4-Only PE-CE, VPN over IPv4-Only Core, 6to4
            softwire -Inter-AS Option-C  . . . . . . . . . . . . . .  20
     5.9.  Test-9 E2E IPv4-Only PE-CE, Global Table over IPv6-Only
            Core, 4to6 softwire -Inter-AS Option-B . . . . . . . . .  21
     5.10. Test-10 E2E IPv4-Only PE-CE, Global Table over IPv6-Only
            Core, 4to6 softwire -Inter-AS Option-C . . . . . . . . .  21
     5.11. Test-11 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core, 4to6
            softwire -Inter-AS Option-B  . . . . . . . . . . . . . .  22



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     5.12. Test-12 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core, 4to6
            softwire -Inter-AS Option-C  . . . . . . . . . . . . . .  22
     5.13. IPv4-Only PE-CE Operational Considerations Testing  . . .  23
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .  23
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  25
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  25
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     11.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   As Enterprises and Service Providers upgrade their brown field or
   green field MPLS/SR core to an IPv6 transport such as MPLS LDPv6, SR-
   MPLSv6 or SRv6, Multiprotocol BGP (MP-BGP) now plays an important
   role in the transition of the Provider (P) core networks and Provider
   Edge (PE) edge networks from IPv4 to IPv6.  Operators have a
   requirement to support IPv6 customers and must be able to support
   IPv6 address family and Sub-Address-Family Virtual Private Network
   (VPN)-IPv6, and Multicast VPN IPv6 customers.

   With this IPv4-only BGP peering design, only IPv4 is configured on
   the PE-CE interface, the Provider Edge (PE) - Customer Edge (CE), the
   IPv4 BGP peer is now used to carry IPv6 (Network Layer Reachability
   Information) NLRI over an IPv4 next hop using 4 byte IPv4 next hop
   encoding while continuing to forward both IPv4 and IPv6 packets.  In
   the framework of this design the PE is no longer Dual Stacked.
   However in the case of the CE, PE-CE link CE side of the link is no
   longer Dual Stacked, however all other internal links within the CE
   domain may or maynot be Dual stacked.

   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).  Historically 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 or VPN-IPv4.  [RFC8950] specifies the extensions
   necessary to allow advertising IPv4 NLRI, Virtual Private Network
   Unicast (VPN-IPv4) NLRI, Multicast Virtual Private Network (MVPN-
   IPv4) NLRI with a Next Hop address that belongs to the IPv6 protocol.
   This comprises of an extended next hop encoding MP-REACH BGP
   capability exchange to allow the address of the Next Hop for IPv4
   NLRI, VPN-IPv4 NLRI and MVPN-IPv4 NLRI to also belong to the IPv6
   Protocol.  [RFC8950] defines the encoding of the Next Hop to
   determine which of the protocols the address actually belongs to, and



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   a new BGP Capability allowing MP-BGP Peers to discover dynamically
   whether they can exchange IPv4 NLRI and VPN-IPv4 NLRI with an IPv6
   Next Hop.

   With the IPv4-Only PE design, IPv6 NLRI will be carried over an IPv4
   Next-hop.  [RFC4798] and [RFC4659] specify how an IPv4 address can be
   encoded inside the next-hop IPv6 address field when IPv6 NLRI needs
   to be advertised with an IPv4 next hop.  [RFC4798] defines how the
   IPv4-mapped IPv6 address format specified in the IPv6 addressing
   architecture [RFC4798] can be used for that purpose when the <AFI/
   SAFI> is IPv6-Unicast <2/1>, Multicast <2/2>, and Labeled Unicast
   <2/4>.  [RFC4659] defines how the IPv4-mapped IPv6 address format as
   well as a null Route Distinguisher as ::FFFF:192.168.1.1 (RD) can be
   used for that purpose when the <AFI/SAFI> is VPN-IPv6 <2/128> MVPN-
   IPv6 <2/129>.  This IPv4-Only PE specification utilizes IPv6 NLRI
   over IPv4 Next hop encoding adopted by the industy to not use IPv4
   mapped IPv6 address defined above, and instead use 4 byte IPv4
   address for the next hop which ultimately set the precedence for the
   adoption of [RFC8950] for 4to6 Softwire IPv4 NLRI over IPv6 next-hop
   using an IPv6 address for the next hop and not a IPv6 mapped IPv4
   address.  The IPv4 next hop encoding for cases where the NLRI
   advertised is different from the next hop encoding such as where IPv6
   NLRI is advertied with IPv4 next hop for for <AFI/SAFI> is
   IPv6-Unicast <2/1>, Multicast <2/2>, and Labeled Unicast <2/4>.
   [RFC4659] defines Null(RD) for <AFI/SAFI> is VPN-IPv6 <2/128> MVPN-
   IPv6 <2/129> but now with a an official new IANA Capability code TBD
   as value 10 "IPv4 Next Hop Encoding".  The IETF standards have not
   been updated with an IANA allocation Capability code for the IPv4
   next hop encoding so this specification fixes that problem with an
   IANA allocated capability codepoint which will now be used for any
   eBGP or iBGP peering as well as the IPv4-Only PE design defined in
   this specification.

   With this IPv4-Only PE Design, BGP peer session can now be treated as
   a pure TCP transport and carry both IPv4 and IPv6 NLRI at the
   Provider Edge (PE) - Customer Edge (CE) over a single IPv4 TCP
   session.  This allows for the elimination of dual stack from the PE-
   CE peering point, and now enable the peering to be IPv4-ONLY.  The
   elimination of IPv6 on the PE-CE peering points translates into OPEX
   expenditure savings of point-to-point infrastructure links as well as
   /127 address space savings and administration and network management
   of both IPv4 and IPv6 BGP peers.  This reduction decreases the number
   of PE-CE BGP peers by fifty percent, which is a tremendous cost
   savings for operators.  This also translates into Major CAPEX savings
   as now operators do not have to migrate their underlay to IPv6 and
   can remain indefinitely on IPv4-Only Core.





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   While the savings exists at the Edge eBGP PE-CE peering, on the core
   side PE to Route Reflector (RR) peering carrying <AFI/SAFI> IPv4
   <2/1>, VPN-IPV4 <2/128>, and Multicasat VPN <2/129>, there is no
   savings as the Provider (P) Core is IPv4 Only and thus can only have
   an IPv4 peer standard 4 byte next hop encoding to carrying IPv4 NLRI
   IPV4 <2/1>, VPN-IPV4 <2/128>, and Multicasat VPN <2/129> over an IPv4
   next hop.

   This core and edge IPv4-Only peering design paradigm change can apply
   to any eBGP peering, public internet or private, which can be either
   Core networks, Data Center networks, Access networks or can be any
   eBGP peering scenario.  This document provides detailed vendor
   specific test cases and test results for the IPv4-Only peering design
   as well as successful test results between five major vendors
   stakeholders in the routing and switching indusrty, Cisco, Juniper,
   Arista, Nokia and Huawei.  With the test results provided for the
   IPv4-Only Edge peering design, the goal is that all other vendors
   around the world that have not been tested will begin to adopt and
   implement this new best practice for eBGP IPv4-Only Edge peering.

2.  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.

3.  Terminology

   Terminolgoy used in defining the IPv6-Only Edge specification.

   AFBR: Address Family Border Router Provider Edge (PE).

   Edge: PE-CE Edge Network Provider Edge - Customer Edge

   Core: P Core Network Provider (P)

   4to6 Softwire : IPv4 edge over an IPv6-Only core

   6to4 Softwire: IPv6 edge over an IPv4-Only core

   E2E: End to End

4.  IPv6-Only Edge Peering Architecture






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4.1.  Problem Statement

   This specification addresses a real issue that has been discussed at
   many operator with extremely large core networks around the world
   related migration to IPv6 underlay transport which can be put off
   indefinitely.  Operators around the world are clamoring for a
   solution that can help solve issues related to IPv4 address depletion
   at these large IXP peering points.  With this solution,
   infrastructure networks such as Core networks, DC networks, Access
   networks as well as any PE-CE public or private network can now
   utilize this IPv4-Only Edge solution and reap the benefits
   immediately on IPv6 address space saving and CAPEX and OPEX savings.


                                          Problem Statement

                        Dual Stacked            Dual Stacked
                             CE                      PE

                          +-------+ IPv4 BGP Peer +-------+
                          |       |---------------|       |
                          |   CE  | IPv6 BGP Peer |  PE   |
                          |       |---------------|       |
                          +-------+               +-------+
                         IPv4 forwarding            IPv4 forwarding
                         IPv6 forwarding            IPv6 forwarding


              Figure 1: Problem Statement - Dual Stack Peering


                               ________
    Dual Stacked     _____    /        \                Dual Stacked
      PE / CE       /     \__/          \___              PE / CE
  +----+  +----+   /                        \        +------+   +-----+
  |    |  |    |  |0====VPN Overlay Tunnel ==0|      |      |   |     |
  |    |  |    |  |                             \    |      |   |     |
  | CE |--| PE |--\         IPv6-Only Core      |----|  PE  |---|  CE |
  |    |  |    |    \0=========Underlay =======0|    |      |   |     |
  +----+  +----+     \                        __/    +------+   +-----+
  IPv4 IPv6 BGP peer  \ IP / MPLS / SR domain /     IPv4 and IPv6 BGP peer
  IPv4 forwarding      \__         __       /          IPv4 forwarding
  IPv6 forwarding         \_______/  \_____/           IPv6 forwarding




          Figure 2: Problem Statement - E2E Dual Stack Edge



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4.2.  IPv4-Only PE-CE Design Solution

   The IPv4-Only Edge design solution provides a means of E2E single
   protocol design solution extension of [RFC5565] Softwire Mesh
   framework from the PE-CE Edge to the Core from ingres so egress
   through the entire operators domain.  This solution eliminates all
   IPv4 addressing from end to end while still providing the same Dual
   Stack functionality of IPv4 and IPv6 packet forwarding from a data
   plane perspective by leveraging the [RFC8950] extended next hop
   encoding so that IPv4 NLRI can be advertised over a single IPv6 pure
   transport TCP session.  This IPv4-Only E2E architecture eliminates
   all IPv4 peering and IPv4 addressing E2E from the ingress CE to
   ingress PE to egress PE to egress CE and all hops along the operator
   E2E path.


                             Solution applicable to
                  any Edge peering scenario - IXP, Core, DC, Access, etc

                   +-------+                +-------+
                   |       |  IPv4 Only     |       |
                   |   CE  |----------------|  PE   |
                   |       |  IPv4 BGP Peer |       |
                   +-------+                +-------+
                  IPv4 forwarding            IPv4 forwarding
                  IPv6 forwarding            IPv6 forwarding


              Figure 3: IPv4-Only Solution Applicability


                                ________
      IPv4-Only       _____    /        \                 IPv4-Only
       PE / CE       /     \__/          \___              PE / CE
   +----+  +----+   /                        \        +------+   +-----+
   |    |  |    |  |0====VPN Overlay Tunnel ==0|      |      |   |     |
   |    |  |    |  |                             \    |      |   |     |
   | CE |--| PE |--\         IPv4-Only Core      |----|  PE  |---|  CE |
   |    |  |    |    \0=========Underlay ===== ==0    |      |   |     |
   +----+  +----+     \                        __/    +------+   +-----+
   IPv6 BGP peer        \IP / MPLS / SR domain /        IPv6 BGP peer
   IPv4 forwarding      \__         __       /          IPv4 forwarding
   IPv6 forwarding         \_______/  \_____/           IPv6 forwarding




                       Figure 4: E2E VPN Solution



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4.3.  IPv4-Only Edge Peering Design

4.3.1.  IPv4-Only Edge Peering Packet Walk

   The IPv4-Only Edge Peering design utilizes two key E2E Softwire Mesh
   Framework scenario's, 4to6 softwire and 6to4 softwire.  The Softwire
   mesh framework concept is based on the overlay and underlay MPLS or
   SR based technology framework, where the underlay is the transport
   layer and the overlay is a Virtual Private Network (VPN) layer, and
   is the the tunneled virtualization layer containing the customer
   payload.  The concept of a 6to4 Softwire is based on transmission of
   IPv6 packets at the edge of the network by tunneling the IPv6 packets
   over an IPv4-Only Core.  The concept of a 4to6 Softwire is also based
   on transmission of IPv4 packets at the edge of the network by
   tunneling the IPv4 packets over an IPv6-Only Core.

   This document describes End to End (E2E) test scenarios that follow a
   packet flow from IPv4-Only attachment circuit from ingress PE-CE to
   egress PE-CE tracing the routing protocol control plane and data
   plane forwarding of IPv4 packets in a 4to6 softwire or 6to4 softwire
   within the IPv4-Only or IPv6-Only Core network.  In both secneario we
   are focusing on IPv4 packets and the control plane and data plane
   forwarding aspects of IPv4 packets from the PE-CE Edge network over
   an IPv4-Only P (Provider) core network or IPv6-Only P (Provider) core
   network.  With this IPv4-Only Edge peering design, the Softwire Mesh
   Framework is not extended beyond the Provider Edge (PE) and continues
   to terminate on the PE router.

4.3.2.  6to4 Softwire IPv4-Only Core packet walk

   6to4 softwire where IPv4-Edge eBGP IPv4 peering where IPv6 packets at
   network Edge traverse a IPv4-Only Core

   In the scenario where IPv6 packets originating from a PE-CE edge are
   tunneled over an MPLS or Segment Routing IPv4 underlay core network,
   the PE and CE only have an IPv6 address configured on the interface.
   In this scenario the IPv6 packets that ingress the CE from within the
   CE AS are over an IPv4-Only interface and are forwarded to an IPv6
   NLRI destination prefix learned from the Pure Transport Single IPv4
   BGP Peer.  In the IPv4-Only Edge peering architecture the PE is
   IPv4-Only as all PE-CE interfaces are IPv4-Only.  However, on the CE,
   the PE-CE interface is the only interface that is IPv4-Only and all
   other interfaces may or may not be IPv4-Only.  Following the data
   plane packet flow, IPv4 packets are forwarded from the ingress CE to
   the IPv4-Only ingress PE where the VPN label imposition push per
   prefix, per-vrf, per-CE occurs and the labeled packet is forwarded
   over a 6to4 softwire IPv4-Only core, to the egress PE where the VPN
   label disposition pop occurs and the native IPv4 packet is forwarded



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   to the egress CE.  In the reverse direction IPv4 packets are
   forwarded from the egress CE to egress PE where the VPN label
   imposition per prefix, per-vrf, per-CE push occurs and the labeled
   packet is forwarded back over the 6to4 softwire IPv4-Only core, to
   the ingress PE where the VPN label disposition pop occurs and the
   native IPv4 packet is forwarded to the ingress CE. . The
   functionality of the IPv4 forwarding plane in this scenario is
   identical from a data plane forwarding perspective to Dual Stack IPv4
   forwarding scenario.










































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                             +--------+   +--------+
                             |  IPv4  |   |  IPv4  |
                             | Client |   | Client |
                             | Network|   | Network|
                             +--------+   +--------+
                                 |   \     /   |
                                 |    \   /    |
                                 |     \ /     |
                                 |      X      |
                                 |     / \     |
                                 |    /   \    |
                                 |   /     \   |
                             +--------+   +--------+
                             |  AFBR  |   |  AFBR  |
                          +--| IPv4/6 |---| IPv4/6 |--+
                          |  +--------+   +--------+  |
          +--------+      |                           |       +--------+
          |  IPv4  |      |                           |       |  IPv4  |
          | Client |      |                           |       | Client |
          | Network|------|            IPv4           |-------| Network|
          +--------+      |            only           |       +--------+
                          |                           |
                          |  +--------+   +--------+  |
                          +--|  AFBR  |---|  AFBR  |--+
                             | IPv4/6 |   | IPv4/6 |
                             +--------+   +--------+
                               |   \     /   |
                               |    \   /    |
                               |     \ /     |
                               |      X      |
                               |     / \     |
                               |    /   \    |
                               |   /     \   |
                            +--------+   +--------+
                            |  IPv6  |   |  IPv4  |
                            | Client |   | Client |
                            | Network|   | Network|
                            +--------+   +--------+



         Figure 5: 6to4 Softwire - IPv6 Edge over an IPv4-Only Core

4.3.3.  4to6 Softwire IPv6-Only Core packet walk

   4to6 softwire where IPv4-Edge eBGP IPv4 peering where IPv6 packets at
   network Edge traverse a IPv6-Only Core




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   In the scenario where IPv6 packets originating from a PE-CE edge are
   tunneled over an MPLS or Segment Routing IPv4 underlay core network,
   the PE and CE only have an IPv4 address configured on the interface.
   In this scenario the IPv6 packets that ingress the CE from within the
   CE AS are over an IPv4-Only interface and are forwarded to an IPv6
   NLRI destination prefix learned from the Pure Transport Single IPv4
   BGP Peer.  In the IPv4-Only Edge peering architecture the PE is
   IPv4-Only as all PE-CE interfaces are IPv4-Only.  However, on the CE,
   the PE-CE interface is the only interface that is IPv4-Only and all
   other interfaces may or may not be IPv4-Only.  Following the data
   plane packet flow, IPv6 packets are forwarded from the ingress CE to
   the IPv4-Only ingress PE where the VPN label imposition push per
   prefix, per-vrf, per-CE occurs and the labeled packet is forwarded
   over a 4to6 softwire IPv6-Only core, to the egress PE where the VPN
   label disposition pop occurs and the native IPv6 packet is forwarded
   to the egress CE.  In the reverse direction IPv6 packets are
   forwarded from the egress CE to egress PE where the VPN label
   imposition per prefix, per-vrf, per-CE push occurs and the labeled
   packet is forwarded back over the 4to6 softwire IPv6-Only core, to
   the ingress PE where the VPN label disposition pop occurs and the
   native IPv6 packet is forwarded to the ingress CE. . The
   functionality of the IPv4 forwarding plane in this scenario is
   identical from a data plane forwarding perspective to Dual Stack IPv4
   / IPv6 forwarding scenario.



























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                             +--------+   +--------+
                             |  IPv4  |   |  IPv4  |
                             | Client |   | Client |
                             | Network|   | Network|
                             +--------+   +--------+
                                 |   \     /   |
                                 |    \   /    |
                                 |     \ /     |
                                 |      X      |
                                 |     / \     |
                                 |    /   \    |
                                 |   /     \   |
                             +--------+   +--------+
                             |  AFBR  |   |  AFBR  |
                          +--| IPv4/6 |---| IPv4/6 |--+
                          |  +--------+   +--------+  |
          +--------+      |                           |       +--------+
          |  IPv6  |      |                           |       |  IPv6  |
          | Client |      |                           |       | Client |
          | Network|------|            IPv6           |-------| Network|
          +--------+      |            only           |       +--------+
                          |                           |
                          |  +--------+   +--------+  |
                          +--|  AFBR  |---|  AFBR  |--+
                             | IPv4/6 |   | IPv4/6 |
                             +--------+   +--------+
                               |   \     /   |
                               |    \   /    |
                               |     \ /     |
                               |      X      |
                               |     / \     |
                               |    /   \    |
                               |   /     \   |
                            +--------+   +--------+
                            |  IPv4  |   |  IPv4  |
                            | Client |   | Client |
                            | Network|   | Network|
                            +--------+   +--------+




         Figure 6: 4to6 Softwire - IPv4 Edge over an IPv6-Only Core

4.4.  RFC5549 and RFC8950 Applicability to IPv4-Only PE Design






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4.4.1.  IPv4-Only Edge Peering design next-hop encoding

   This section describes [RFC8950] next hop encoding updates to
   [RFC5549] applicability to this specification.  IPv4-Only eBGP Edge
   PE-CE peering to carry IPv4 Unicast NLRI <AFI/SAFI> IPv4 <1/1> over
   an IPv6 next hop BGP capability extended hop encoding IANA capability
   codepoint value 5 defined is applicable to both [RFC5549] and
   [RFC8950] as IPv4 Unicast NLRI <AFI/SAFI> IPv4 <1/1> does not change
   in the RFC updates.

   IPv4 packets over an IPv6-Only core 4to6 Softwire E2E packet flow is
   part of the IPv6-Only PE design and this same style next hop encoding
   applies to 6to4 Softwire IPv6 NLRI over IPv4 next hop with 4 byte
   Next hop encoding and not IPv4 mapped IPv6 address.  [RFC8950]
   updates [RFC5549] for <AFI/SAFI> VPN-IPV4 <1/128>, and Multicasat VPN
   <1/129>

4.4.2.  IPv4-Only PE Design Next Hop Encoding

   This section describes IPv4 Next Hop Encoding for IPv6 NLRI over an
   IPv4 Next hop.

   With the IPv4-Only PE design, IPv6 NLRI will be carried over an IPv4
   Next-hop.  [RFC4798] and [RFC4659] specify how an IPv4 address can be
   encoded inside the next-hop IPv6 address field when IPv6 NLRI needs
   to be advertised with an IPv4 next hop.  [RFC4798] defines how the
   IPv4-mapped IPv6 address format specified in the IPv6 addressing
   architecture [RFC4798] can be used for that purpose when the <AFI/
   SAFI> is IPv6-Unicast <2/1>, Multicast <2/2>, and Labeled Unicast
   <2/4>.  [RFC4659] defines how the IPv4-mapped IPv6 address format as
   well as a null Route Distinguisher as ::FFFF:192.168.1.1 (RD) can be
   used for that purpose when the <AFI/SAFI> is VPN-IPv6 <2/128> MVPN-
   IPv6 <2/129>.  This IPv4-Only PE specification utilizes IPv6 NLRI
   over IPv4 Next hop encoding adopted by the industy to not use IPv4
   mapped IPv6 address defined above, and instead use 4 byte IPv4
   address for the next hop which ultimately set the precedence for the
   adoption of [RFC8950] for 4to6 Softwire IPv4 NLRI over IPv6 next-hop.
   The IPv4 next hop encoding for cases where the NLRI advertised is
   different from the next hop encoding such as where IPv6 NLRI is
   advertied with IPv4 next hop for for <AFI/SAFI> is IPv6-Unicast
   <2/1>, Multicast <2/2>, and Labeled Unicast <2/4>.  [RFC4659] defines
   Null(RD) for <AFI/SAFI> is VPN-IPv6 <2/128> MVPN-IPv6 <2/129> but now
   with a an official new IANA Capability code TBD as value 10 "IPv4
   Next Hop Encoding".  The IETF standards have not been updated with an
   IANA allocation Capability code for the IPv4 next hop encoding so
   this specification fixes that with an IANA allocated codepoint which
   will now be used for any eBGP or iBGP peering as well as the
   IPv4-Only PE design defined in this specification.



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   With this specification when VPN-IPv6 AFI/SAFI 2/128, MVPN-IPv6 AFI/
   SAFI 2/129 is used, the next-hop address is encoded as an IPv4
   address with a length of 12 bytes.  The next-hop address is now
   encoded for VPN-IPv6 AFI/SAFI with a length of 12 bytes.  The 12 byte
   next hop includes 4 byte IPv4 address plus 8 byte Route
   Distinguisher.  This document modifies how the next-hop address is
   encoded to accommodate all existing implementations and bring
   consistency with VPN-IPv6, MVPN-IPv6 and 6PE.  As all known and
   deployed implementations are interoperable today and use the new
   proposed encoding, the change does not break existing
   interoperability.  This change is applicable to all iBGP and eBGP
   peering as well as the IPv4-Only PE, PE-CE edge and Inter-AS peering
   design for the IPv4 next hop encoding E2E test case of IPv4 packets
   over and IPv4-Only core 6to4 Softwire.  In this test case IPv6
   Unicast NLRI <AFI/SAFI> IPv4 <1/1> is advertised over the PE to RR
   core peering 6to4 softwire in <AFI/SAFI> VPN-IPV6 <2/128> MVPN-IPv6
   <2/129>.  In this test cases label allocation mode comes into play
   which is discussed in a subsequent section.

   This document defines with the new IANA BGP Capability codepoint
   allocation next hop encoding of MP_REACH_NLRI with:

   *  Specifically, this document allows advertising the MP_REACH_NLRI
      attribute [RFC2545] with this content:

   Advertising with [RFC2545] MP_REACH_NLRI with:

   *  AFI = 2

   *  SAFI = 1, 2 or 4

   *  Length of Next Hop Address = 4

   *  Specifically, this document allows advertising the MP_REACH_NLRI
      attribute [RFC2545] with this content:

   Advertising with [RFC2545] MP_REACH_NLRI with:

   *  AFI = 2

   *  SAFI = 128 or 129

   *  Length of Next Hop Address = 8

   *  Next Hop Address = VPN-IPv4 address of next hop with an 8-octet RD
      set to zero.





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5.  IPv4-Only PE Design Edge E2E Test Cases

   Proof of conept interoperability testing of the 4 test cases between
   the 5 vendors Cisco, Juniper, Arista, Nokia and Huawei.

   Cisco, Juniper, Arista, Nokia, Huawei, platform, code revision and
   test results for all use cases

   Cisco: Edge Router- XR ASR 9910 IOS XR 7.4.1, Core Router- NCS 6000
   7.2.2, CRS-X 6.7.4

   Juniper: Edge Router- MX platform MX480, MX960, Core Router- PTX
   Platform PTX5000, PTC10K8 (JUNOS and EVO) Release 20.4R2

   Nokia: Edge and Core-7750 Service Router, Release R21

   Huawei: Edge and Core-VRPv8, Release VRP-V800R020C10

   Arista:

   Intra-AS tests PE-CE Edge Peering IPv4-Only Core, IPv6-Only Core,
   Global Table (GRT) and IP VPN

   AFI/SAFI IPv4-Unicast SAFI IPv6-Unicast SAFI

   IPv4 Core:

   Test-1 Global table (6PE)

   Test-2 IP VPN

   Global table IPv6

   IPv6 Core:

   Test-3 Global table

   Test-4 IP VPN

   Inter-AS Options tests IPv4-Only Core, IPv6-Only Core, Global
   Table (GRT) and IP VPN

   AFI/SAFI VPN and MVPN

   IPv4-Only Core

   Test-5 Global table 6PE Option-B (Segmented LSP stitched IPv4 Core -
   Inter-AS Link IPv6-Only PE - IPv4 Core)



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   Test-6 Global table 6PE Option-C (Redistribute IPv4 Loopbacks into
   BGP-LU AFI/SAFI 2/6)

   Test-7 IP VPN Inter AS Option-B (Segmented LSP stitched IPv4 Core -
   Inter-AS Link IPv6-Only PE - IPv4 Core)

   Test-8 IP VPN Inter AS Option-C (Redistribute IPv4 Loopbacks into
   BGP-LU AFI/SAFI 2/6)

   IPv6-Only Core

   Test-9 Global table Option-B

   Test-10 Global table Option-C

   Test-11 IP VPN Inter AS Option-B

   Test-12 IP VPN Inter AS Option-C

5.1.  Test-1 E2E IPv4-Only PE-CE, Global Table over IPv4-Only Core(6PE),
      6to4 softwire


                                ________
      IPv4-Only       _____    /        \                 IPv4-Only
       PE / CE       /     \__/          \___              PE / CE
   +----+  +----+   /                        \        +------+   +-----+
   |    |  |    |  |                          |_      |      |   |     |
   |    |  |    |  |                             \    |      |   |     |
   | CE |--| PE |--\         IPv4-Only Core      |----|  PE  |---|  CE |
   |    |  |    |    \0=========Underlay =======0|    |      |   |     |
   +----+  +----+     \                        __/    +------+   +-----+
   IPv4 BGP peer       \     MPLS / SR domain /         IPv4 BGP peer
   IPv4 forwarding      \__         __       /          IPv4 forwarding
   IPv6 forwarding         \_______/  \_____/           IPv6 forwarding




   Figure 7: Test-1 E2E IPv4-Only PE-CE, Global Table over IPv4-Only
                               Core (6PE)

5.2.  Test-2 E2E IPv4-Only PE-CE, VPN over IPv4-Only Core, 6to4 Softwire








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                                ________
      IPv4-Only       _____    /        \                 IPv4-Only
       PE / CE       /     \__/          \___              PE / CE
   +----+  +----+   /                        \        +------+   +-----+
   |    |  |    |  | 0====VPN Overlay Tunnel ==0|     |      |   |     |
   |    |  |    |  |                             \    |      |   |     |
   | CE |--| PE |--\         IPv4-Only Core      |----|  PE  |---|  CE |
   |    |  |    |    \0=========Underlay =======0|    |      |   |     |
   +----+  +----+     \                        __/    +------+   +-----+
   IPv4 BGP peer       \   MPLS / SR domain   /         IPv4 BGP peer
   IPv4 forwarding      \__         __       /          IPv4 forwarding
   IPv6 forwarding         \_______/  \_____/           IPv6 forwarding




     Figure 8: Test-2 E2E IPv4-Only PE-CE, VPN over IPv4-Only Core

   Huawei: Edge and Core-VRPv8, Release VRP-V800R020C10

5.3.  Test-3 E2E IPv4-Only PE-CE, Global Table over IPv6-Only Core
      (4PE), 4to6 Softwire


                                ________
      IPv4-Only       _____    /        \                 IPv4-Only
       PE / CE       /     \__/          \___              PE / CE
   +----+  +----+   /                        \        +------+   +-----+
   |    |  |    |  |                          |_      |      |   |     |
   |    |  |    |  |                             \    |      |   |     |
   | CE |--| PE |--\         IPv4-Only Core      |----|  PE  |---|  CE |
   |    |  |    |    \0=========Underlay =======0|    |      |   |     |
   +----+  +----+     \                        __/    +------+   +-----+
   IPv4 BGP peer       \     MPLS / SR domain /         IPv4 BGP peer
   IPv4 forwarding      \__         __       /          IPv4 forwarding
   IPv6 forwarding         \_______/  \_____/           IPv6 forwarding




   Figure 9: Test-3 E2E IPv4-Only PE-CE, Global Table over IPv6-Only
                               Core (4PE)

5.4.  Test-4 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core, 4to6 Softwire







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                                ________
      IPv4-Only       _____    /        \                 IPv4-Only
       PE / CE       /     \__/          \___              PE / CE
   +----+  +----+   /                        \        +------+   +-----+
   |    |  |    |  | 0====VPN Overlay Tunnel ==0|     |      |   |     |
   |    |  |    |  |                             \    |      |   |     |
   | CE |--| PE |--\         IPv4-Only Core      |----|  PE  |---|  CE |
   |    |  |    |    \0=========Underlay =======0|    |      |   |     |
   +----+  +----+     \                        __/    +------+   +-----+
   IPv4 BGP peer       \    MPLS / SR domain  /         IPv4 BGP peer
   IPv4 forwarding      \__         __       /          IPv4 forwarding
   IPv6 forwarding         \_______/  \_____/           IPv6 forwarding




     Figure 10: Test-4 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core

5.5.  Test-5 E2E IPv4-Only PE-CE, Global Table over IPv4-Only Core(6PE),
      6to4 softwire -Inter-AS Option-B



                    Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv4-Only Core|----|IPv4-Only Core|--|PE|-|CE|
     |  | |    |  |0=Underlay==0  |    |0==Underlay==0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding



          Figure 11: Test-5 E2E IPv4-Only PE-CE, Global Table over
                  IPv4-Only Core (6PE) - Inter-AS Option-B

5.6.  Test-6 E2E IPv4-Only PE-CE, Global Table over IPv4-Only Core(6PE),
      6to4 softwire -Inter-AS Option-C








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                   Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv4-Only Core|----|IPv4-Only Core|--|PE|-|CE|
     |  | |    |  |0=Underlay==0  |    |0==Underlay==0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding




          Figure 12: Test-6 E2E IPv4-Only PE-CE, Global Table over
                  IPv4-Only Core (6PE) - Inter-AS Option-C

5.7.  Test-7 E2E IPv4-Only PE-CE, VPN over IPv4-Only, 6to4 softwire -
      Inter-AS Option-B


                  Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv4-Only Core|----|IPv4-Only Core|--|PE|-|CE|
     |  | |    |  |0=Overlay===0  |    |0==Overlay===0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding




      Figure 13: Test-7 E2E IPv4-Only PE-CE, VPN over IPv4-Only Core -
                             Inter-AS Option-B

5.8.  Test-8 E2E IPv4-Only PE-CE, VPN over IPv4-Only Core, 6to4 softwire
      -Inter-AS Option-C







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                  Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv4-Only Core|----|IPv4-Only Core|--|PE|-|CE|
     |  | |    |  |0=Overlay===0  |    |0==Overlay===0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding




      Figure 14: Test-8 E2E IPv4-Only PE-CE, VPN over IPv4-Only Core -
                             Inter-AS Option-C

5.9.  Test-9 E2E IPv4-Only PE-CE, Global Table over IPv6-Only Core, 4to6
      softwire -Inter-AS Option-B


                  Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv6-Only Core|----|IPv6-Only Core|--|PE|-|CE|
     |  | |    |  |0=Underlay==0  |    |0==Underlay==0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding




          Figure 15: Test-9 E2E IPv4-Only PE-CE, Global Table over
                    IPv6-Only Core - Inter- AS Option-B

5.10.  Test-10 E2E IPv4-Only PE-CE, Global Table over IPv6-Only Core,
       4to6 softwire -Inter-AS Option-C







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                  Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv6-Only Core|--- |IPv6-Only Core|--|PE|-|CE|
     |  | |    |  |0=Underlay==0  |    |0==Underlay==0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding




         Figure 16: Test-10 E2E IPv4-Only PE-CE, Global Table over
                     IPv6-Only Core - Inter-AS Option-C

5.11.  Test-11 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core, 4to6
       softwire -Inter-AS Option-B


                  Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv6-Only Core|--- |IPv6-Only Core|--|PE|-|CE|
     |  | |    |  |0=Overlay===0  |    |0==Overlay===0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding




     Figure 17: Test-11 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core -
                             Inter-AS Option-B

5.12.  Test-12 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core, 4to6
       softwire -Inter-AS Option-C







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                  Inter-AS ASBR-ASBR link is IPv6-Only PE
     IPv6-Only       __________          __________      IPv6-Only
      PE / CE       /          \        /          \      PE / CE
     +--+ +----+   /            \      /            \    +--+ +--+
     |  | |    |  |    AS 1      \     |    AS 2     \   |  | |  |
     |  | |    |  |               \IPv6|              \  |  | |  |
     |CE|-| PE |--| IPv6-Only Core|--- |IPv6-Only Core|--|PE|-|CE|
     |  | |    |  |0=Overlay===0  |    |0==Overlay===0|  |  | |  |
     +--+ +----+   \             /     \             /   +--+ +--+
     IPv6 BGP peer  \ MPLS/SR   /       \ MPLS/SR   /   IPv6 BGP peer
     IPv4 forwarding \_________/         \_________/    IPv4 forwarding
     IPv6 forwarding                                    IPv6 forwarding




     Figure 18: Test-12 E2E IPv4-Only PE-CE, VPN over IPv6-Only Core -
                             Inter-AS Option-C

5.13.  IPv4-Only PE-CE Operational Considerations Testing


                       Ping CE to PE when destination prefix is withdrawn
                       Traceroute CE to PE and test all ICMPv4 and ICMPv6 type codes

                   +-------+                +-------+
                   |       |  IPv4 Only     |       |
                   |   CE  |----------------|  PE   |
                   |       |  IPv4 BGP Peer |       |
                   +-------+                +-------+
                  IPv4 forwarding            IPv4 forwarding
                  IPv6 forwarding            IPv6 forwarding


                 Figure 19: Ping and Trace Test Case

6.  Operational Considerations

   With a single IPv4 Peer carrying both IPv4 and IPv6 NLRI there are
   some operational considerations in terms of what changes and what
   does not change.

   What does not change with a single IPv6 transport peer carrying IPv4
   NLRI and IPv6 NLRI below:

   Routing Policy configuration is still separate for IPv4 and IPv6
   configured by capability as previously.




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   Layer 1, Layer 2 issues such as one-way fiber or fiber cut will
   impact both IPv4 and IPv6 as previously.

   If the interface is in the Admin Down state, the IPv6 peer would go
   down, and IPv4 NLRI and IPv6 NLRI would be withdrawn as previously.

   Changes resulting from a single IPv4 transport peer carrying IPv4
   NLRI and IPv6 NLRI below:

   Physical interface is no longer dual stacked.

   Any change in IPv4 address will impact both IPv4 and IPv6 NLRI
   exchange.

   Single BFD session for both IPv4 and IPv6 NLRI fate sharing as the
   session is now tied to the transport, which now is only IPv4 address
   family.

   Both IPv4 and IPv6 peer now exists under the IPv4 address family
   configuration.

   Fate sharing of IPv4 and IPv6 address family from a logical
   perspective now carried over a single physical IPv4 peer.

   From an operations perspective, prior to elimination of IPv6 peers,
   an audit is recommended to identify and IPv4 and IPv6 peering
   incongruencies that may exist and to rectify them.  No operational
   impacts or issues are expected with this change.

   With MPLS VPN overlay, per-CE next-hop label allcoation mode where
   both IPv4 and IPv6 prefixes have the same label in no table lookup
   pop-n-forward mode should be taken into consideration.

7.  IANA Considerations

   This document defines a new Capability Code to indicate the Extended
   Next Hop Encoding capability in the [RFC5492] Capabilities Optional
   Parameter.  The value for this new Capability Code is 10, which is in
   the range set aside for allocation using the "IETF Review" policy
   defined in [RFC5226].











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8.  Security Considerations

   The extensions defined in this document allow BGP to propagate
   reachability information about IPv6 prefixes over an MPLS or SR
   IPv4-Only core network.  As such, no new security issues are raised
   beyond those that already exist in BGP-4 and the use of MP-BGP for
   IPv6.  Both IPv4 and IPv6 peers exist under the IPv6 address family
   configuration.  The security features of BGP and corresponding
   security policy defined in the ISP domain are applicable.  For the
   inter-AS distribution of IPv4 routes according to case (a) of
   Section 4 of this document, no new security issues are raised beyond
   those that already exist in the use of eBGP for IPv6 [RFC2545].

9.  Acknowledgments

   Thanks to Kaliraj Vairavakkalai, Linda Dunbar, Aijun Wang, Eduardfor
   Vasilenko, Joel Harlpern, Michael McBride, Ketan Talaulikar for
   review comments.

10.  Contributors

   The following people contributed substantive text to this document:

       Mohana Sundari
       EMail: mohanas@juniper.net


11.  References

11.1.  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/info/rfc2119>.

   [RFC2545]  Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
              Extensions for IPv6 Inter-Domain Routing", RFC 2545,
              DOI 10.17487/RFC2545, March 1999,
              <https://www.rfc-editor.org/info/rfc2545>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.



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   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <https://www.rfc-editor.org/info/rfc5492>.

   [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/info/rfc8174>.

   [RFC8277]  Rosen, E., "Using BGP to Bind MPLS Labels to Address
              Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
              <https://www.rfc-editor.org/info/rfc8277>.

11.2.  Informative References

   [I-D.ietf-idr-dynamic-cap]
              Chen, E. and S. R. Sangli, "Dynamic Capability for BGP-4",
              Work in Progress, Internet-Draft, draft-ietf-idr-dynamic-
              cap-16, 21 October 2021, <https://www.ietf.org/archive/id/
              draft-ietf-idr-dynamic-cap-16.txt>.

   [RFC4659]  De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
              "BGP-MPLS IP Virtual Private Network (VPN) Extension for
              IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006,
              <https://www.rfc-editor.org/info/rfc4659>.

   [RFC4684]  Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
              R., Patel, K., and J. Guichard, "Constrained Route
              Distribution for Border Gateway Protocol/MultiProtocol
              Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
              Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
              November 2006, <https://www.rfc-editor.org/info/rfc4684>.

   [RFC4798]  De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
              "Connecting IPv6 Islands over IPv4 MPLS Using IPv6
              Provider Edge Routers (6PE)", RFC 4798,
              DOI 10.17487/RFC4798, February 2007,
              <https://www.rfc-editor.org/info/rfc4798>.




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   [RFC4925]  Li, X., Ed., Dawkins, S., Ed., Ward, D., Ed., and A.
              Durand, Ed., "Softwire Problem Statement", RFC 4925,
              DOI 10.17487/RFC4925, July 2007,
              <https://www.rfc-editor.org/info/rfc4925>.

   [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/info/rfc5549>.

   [RFC5565]  Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
              Framework", RFC 5565, DOI 10.17487/RFC5565, June 2009,
              <https://www.rfc-editor.org/info/rfc5565>.

   [RFC6074]  Rosen, E., Davie, B., Radoaca, V., and W. Luo,
              "Provisioning, Auto-Discovery, and Signaling in Layer 2
              Virtual Private Networks (L2VPNs)", RFC 6074,
              DOI 10.17487/RFC6074, January 2011,
              <https://www.rfc-editor.org/info/rfc6074>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.

   [RFC6514]  Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
              Encodings and Procedures for Multicast in MPLS/BGP IP
              VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
              <https://www.rfc-editor.org/info/rfc6514>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8950]  Litkowski, S., Agrawal, S., Ananthamurthy, K., and K.
              Patel, "Advertising IPv4 Network Layer Reachability
              Information (NLRI) with an IPv6 Next Hop", RFC 8950,
              DOI 10.17487/RFC8950, November 2020,
              <https://www.rfc-editor.org/info/rfc8950>.

Authors' Addresses

   Gyan Mishra
   Verizon Inc.
   Email: gyan.s.mishra@verizon.com






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   Jeff Tantsura
   Microsoft, Inc.
   Email: jefftant.ietf@gmail.com
















































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