BESS Working Group                                             G. Mishra
Internet-Draft                                              Verizon Inc.
Intended status: Standards Track                             J. Tantsura
Expires: 22 December 2022                                Microsoft, Inc.
                                                            20 June 2022


                      IPv4-Only PE Design All SAFI
           draft-mishra-bess-ipv4-only-pe-design-all-safi-00

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.

   [I-D.mishra-bess-ipv4-only-pe-design] 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.


















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   [I-D.mishra-bess-ipv4-only-pe-design] 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 details an important External BGP (eBGP) PE-PE Inter-AS
   IPv6-Only peering design that leverages the MP-BGP capability
   exchange by using IPv6 peering as pure transport, allowing all and
   any 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 for all Address Family
   Identifiers (AFI) and Subsequent Address Family Identifiers(SAFI).
   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 IPv4-Only PE Design, IPv6 address MUST not be
   configured on the the Provider Edge (PE) - Customer Edge (CE), or
   Inter-AS ASBR (Autonomous System Boundary Router) to ASBR (Autonomous
   System Boundary Router) PE-PE Provider Edge (PE) - Provider Edge
   (PE).  From a control plane perspective a single IPv4-Only peer 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 to PE Inter-AS peering interface for both IPv4 and IPv6 packet
   forwarding.  This document defines the IPv4-Only PE Design as a new
   PE-CE Edge and ASBR-ASBR PE-PE Inter-AS BGP peering Standard which is
   described in the POC testing document
   [I-D.mishra-bess-ipv4-only-pe-design] which is now extended to
   support to all AFI/SAFI ubiquitously.  As service providers migrate
   to Segment Routing architecture SR-MPLS and SRv6, VPN overlay exsits
   as well, and thus Inter-AS options Option-A, Option-B, Option-AB and
   Option-C are still applicable and thus this extension of IPv4-Only
   peering architecure extension to Inter-AS peering is very relevant to
   Segment Routing as well.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.



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Copyright Notice

   Copyright (c) 2022 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
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   7
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  IPv4-Only PE-CE Design ALL SAFI Solution  . . . . . . . . . .   8
     4.1.  IPv4-Only Edge Peering Design . . . . . . . . . . . . . .   9
       4.1.1.  IPv4-Only PE Design ALL SAFI 6to4 Softwire IPv4-Only
               Core packet walk  . . . . . . . . . . . . . . . . . .   9
       4.1.2.  IPv4-Only PE Design ALL SAFI 6to4 Softwire - IPv6 Edge
               over an IPv4-Only Core  . . . . . . . . . . . . . . .   9
       4.1.3.  IPv4-Only PE Design ALL SAFI 4to6 Softwire - IPv4 Edge
               over an IPv6-Only Core  . . . . . . . . . . . . . . .  11
   5.  RFC5549 and RFC8950 Applicability to IPv4-Only PE Design  . .  13
     5.1.  IPv4-Only Edge Peering design next-hop encoding . . . . .  14
     5.2.  IPv4-Only PE Design Next Hop Encoding . . . . . . . . . .  14
   6.  IPv4-Only PE Design Edge E2E Design for ALL AFI/SAFI  . . . .  16
     6.1.  IPv4-Only PE Design All SAFI Case-1 E2E IPv4-Only PE-CE,
            Global Table over IPv4-Only Core(6PE), 6to4 softwire . .  16
     6.2.  IPv4-Only PE Design All SAFI Case-2 E2E IPv4-Only PE-CE,
            VPN over IPv4-Only Core, 6to4 Softwire . . . . . . . . .  16




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     6.3.  IPv4-Only PE Design All SAFI Case-3 E2E IPv4-Only PE-CE,
            Global Table over IPv6-Only Core (4PE), 4to6 Softwire  .  17
     6.4.  IPv4-Only PE Design All SAFI Case-4 E2E IPv4-Only PE-CE,
            VPN over IPv6-Only Core, 4to6 Softwire . . . . . . . . .  17
     6.5.  IPv4-Only PE Design All SAFI Case-5 E2E IPv4-Only PE-CE,
            Global Table over IPv4-Only Core(6PE), 6to4 softwire
            -Inter-AS Option-B . . . . . . . . . . . . . . . . . . .  18
     6.6.  IPv4-Only PE Design All SAFI Case-6 E2E IPv4-Only PE-CE,
            Global Table over IPv4-Only Core(6PE), 6to4 softwire
            -Inter-AS Option-C . . . . . . . . . . . . . . . . . . .  18
     6.7.  IPv4-Only PE Design All SAFI Case-7 E2E IPv4-Only PE-CE,
            VPN over IPv4-Only, 6to4 softwire -Inter-AS Option-B . .  19
     6.8.  IPv4-Only PE Design All SAFI Case-8 E2E IPv4-Only PE-CE,
            VPN over IPv4-Only Core, 6to4 softwire -Inter-AS
            Option-C . . . . . . . . . . . . . . . . . . . . . . . .  19
     6.9.  IPv4-Only PE Design All SAFI Case-9 E2E IPv4-Only PE-CE,
            Global Table over IPv6-Only Core, 4to6 softwire -Inter-AS
            Option-B . . . . . . . . . . . . . . . . . . . . . . . .  20
     6.10. IPv4-Only PE Design All SAFI Case-10 E2E IPv4-Only PE-CE,
            Global Table over IPv6-Only Core, 4to6 softwire -Inter-AS
            Option-C . . . . . . . . . . . . . . . . . . . . . . . .  20
     6.11. IPv4-Only PE Design All SAFI Case-11 E2E IPv4-Only PE-CE,
            VPN over IPv6-Only Core, 4to6 softwire -Inter-AS
            Option-B . . . . . . . . . . . . . . . . . . . . . . . .  21
     6.12. IPv4-Only PE Design All SAFI Case-12 E2E IPv4-Only PE-CE,
            VPN over IPv6-Only Core, 4to6 softwire -Inter-AS
            Option-C . . . . . . . . . . . . . . . . . . . . . . . .  21
   7.  IPv6-Only PE Design ALL AFI/SFI Operational Considerations  .  22
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  23
   11. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  23
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     12.2.  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.




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   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
   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>.



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   [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.

   This document defines the IPv4-Only PE Design Architecture details
   for External BGP (eBGP) PE-PE Inter-AS IPv6-Only peering design that
   leverages the MP-BGP capability exchange by using IPv6 peering as
   pure transport, allowing all and any 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 for all Address Family Identifiers (AFI) and Subsequent
   Address Family Identifiers(SAFI).  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 IPv6-Only PE
   Design, IPv6 address MUST not be configured on the the Provider Edge
   (PE) - Customer Edge (CE), or Inter-AS ASBR (Autonomous System
   Boundary Router) to ASBR (Autonomous System Boundary Router) PE-PE
   Provider Edge (PE) - Provider Edge (PE).  From a control plane
   perspective a single IPv4-Only peer MUST be configured for both IPv4
   and IPv6 routing updates, and from a data plane forwarindg
   perspective only an IPv4 address MUST be configured on the PE-CE Edge
   or ASBR-ASBR, PE to PE Inter-AS peering interface for both IPv4 and
   IPv6 packet forwarding for all AFI/SAFI.  This document defines the
   IPv4-Only PE Design as a new Intra-AS PE-CE Edge and Inter-AS PE-PE
   BGP peering Standard which is described in the POC testing document
   in detail, [I-D.mishra-bess-ipv4-only-pe-design] which is now
   extended for applicability to to all AFI/SAFI ubiquitously.  As
   service providers migrate to Segment Routing architecture SR-MPLS and
   SRv6, VPN overlay exsits as well, and thus Inter-AS options Option-A,



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   Option-AB and Option-C are still applicable and thus this extension
   of IPv4-Only peering architecure extension to Inter-AS peering is
   very relevant to Segment Routing as well as well as any other
   applicable AFI/SAFI is now as well relevant.

   This IPv4-Only PE ALL SAFI Design details an important External BGP
   (eBGP) PE-PE Inter-AS IPv4-Only peering design that leverages the MP-
   BGP capability exchange by using IPv6 peering as pure transport,
   allowing all and any 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 for
   all remaining Address Family Identifiers (AFI) and Subsequent Address
   Family Identifiers(SAFI) below as well that can be carried over
   IPv4-Only Inter-AS peerings: <AFI/SAFI> MCAST-VPN [RFC6514] <1/5>,
   NLRI Multi-Segment Pseudowires [RFC7267] <1/6>, BGP Tunnel
   Encapsulation SAFI [RFC9012] <1/7>, MCAST-VPLS [RFC7117] <1/8>, BGP
   SFC [RFC9015] <1/9>, Tunnel SAFI [I-D.nalawade-kapoor-tunnel-safi]
   <1/6>, Virtual Private LAN Service (VPLS) [RFC4761] and [RFC6074]
   <1/5>, BGP MDT SAFI [RFC6037] <1/66>, BGP 4to6 SAFI [RFC5747] <1/67>,
   BGP 6to4 SAFI draft xx <1/8>, Layer 1 VPN Auto-Discovery [RFC5195]
   <1/69>, BGP EVPNs [RFC7432] <1/70>, BGP-LS (VPLS) [RFC7752] <1/71>,
   BGP-LS-EVPN [RFC7752] <72/>, SR-TE Policy SAFI draftxx <1/73>, BGP
   6to4 SAFI draft xx <1/8>, SDN WAN Capabilities draftxx <1/74>,
   Routing Policy SAFI draftxx <1/75>, Classful-Transport SAFI draftxx
   <1/76>, Tunneled Traffic FlowSpec draftxx <1/77>, MCAST-TREE SAFI
   draft xx <1/78>, Route Target Constraints [RFC4684] <1/132>,
   Dissemination of Flow Specification Rules [RFC8955] <1/133>, L3 VPN
   Dissemination of Flow Specification Rules [RFC8955] <1/1344>, VPN
   Auto-Discovery SAFI draftxx <1/140>

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)




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

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

   E2E: End to End

4.  IPv4-Only PE-CE Design ALL SAFI Solution

   The IPv4-Only Edge design solution applies to any and all IPv4
   Network Layer Reachability Information (NLRI) and IPv6 Network Layer
   Reachability Information (NLRI) over an IPv4-Only BGP Peering
   session.

   IPv4-Only PE Design ALL SAFI can be broken up into the following
   design scenario's below:

   Edge Customer NLRI IPv4 or IPV6 related AFI/SAFI (PE-CE): 1/1 2/1
   (Unicast), 1/2 2/2 (Multicast)

   Inter-AS Customer NLRI IPv4 or IPV6 related AFI/SAFI (ASBR-ASBR): 1/1
   2/1 (Unicast), 1/2 2/2 (Multicast), 1/128 2/128 (VPN), 1/129 2/129
   (MVPN), 1/4 2/4 BGP-LU (6PE/4PE), 1/140 2/140 (BGP VPN Auto
   Discovery)

   Inter-AS Multicast NLRI IPv4 or IPV6 related AFI/SAFI (ASBR-ASBR):
   1/5 2/5 (MCAST-VPN) , 1/8 2/8 (MCAST-VPLS), 1/66 2/66 (BGP MDT-SAFI),
   1/78 2/78 (MCAST-TREE)

   PE to Controller NLRI IPv4 or IPV6 related AFI/SAFI 1/71 2/71 (BGP-
   LS), 1/72 2/72 (BGP-LS VPN), 1/75 2/75 (Routing Policy SAFI), 1/80
   2/80 BGP-LS-SPF

   Inter-AS L1 VPN, L2 VPN NLRI IPv4 or IPV6 related AFI/SAFI (ASBR-
   ASBR) 1/65 2/65 (VPLS), 1/70 2/70 (BGP EVPN), 1/69 2/69 (L1 VPN)

   Inter-AS BGP FlowSpec, Optimizations and SFC NLRI IPv4 or IPV6
   related AFI/SAFI (ASBR-ASBR) 1/132 2/132 (RTC), 1/133 2/133 (BGP
   FlowSpec), 1/134 2/134 (VPN BGP FlowSpec), 1/9 2/9 (BGP SFC)

   Inter-AS BGP Policy - SR-TE Policy, SD-WAN Policy NLRI IPv4 or IPV6
   related AFI/SAFI (ASBR-ASBR) 1/73 2/73 (SR-TE), 1/74 2/74 (SD-WAN
   Capabilities)









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                                  Solution applicable to all AFI/SAFI
                                  AFI/SAFI 1/X 2/X  Where X = ALL SAFI

                        +-------+                +-------+
                        |   AS1 |  IPv6 Only     |  AS2  |
                        |   PE1 |----------------|  PE2  |
                        | (ASBR)|  IPv6 BGP Peer |(ASBR) |
                        +-------+                +-------+
                       IPv4 forwarding            IPv4 forwarding
                       IPv6 forwarding            IPv6 forwarding


         Figure 1: IPv4-Only Solution Applicability to ALL AFI/SAFI

4.1.  IPv4-Only Edge Peering Design

4.1.1.  IPv4-Only PE Design ALL SAFI 6to4 Softwire IPv4-Only Core 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.

4.1.2.  IPv4-Only PE Design ALL SAFI 6to4 Softwire - IPv6 Edge over an
        IPv4-Only Core

   6to4 softwire where IPv4-Edge eBGP IPv4 peering where IPv6 packets at
   network Edge traverse a IPv4-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 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
   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 2: 6to4 Softwire - IPv6 Edge over an IPv4-Only Core

4.1.3.  IPv4-Only PE Design ALL SAFI 4to6 Softwire - IPv4 Edge over an
        IPv6-Only Core

   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 3: 4to6 Softwire - IPv4 Edge over an IPv6-Only Core

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






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5.1.  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>

5.2.  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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6.  IPv4-Only PE Design Edge E2E Design for ALL AFI/SAFI

   Listed below are the following IPv4-Only PE Design ALL SAFI design
   scenario's:

   <AFI/SAFI> IPv4 Unicast <1/1>, IPv6 Unicast <2/1>, VPN-IPV4 <1/128>,
   VPN-IPV6 <2/128>, Multicasat VPN <1/129>, Multicasat VPN <2/129>,BGP-
   LU IPV4 (GRT) <1/4>

6.1.  IPv4-Only PE Design All SAFI Case-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 4: Design Solution-1 E2E IPv4-Only PE-CE, Global
                    Table over IPv4-Only Core (6PE)

6.2.  IPv4-Only PE Design All SAFI Case-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 5: Design Solution-2 E2E IPv4-Only PE-CE, VPN over
                             IPv4-Only Core

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

6.3.  IPv4-Only PE Design All SAFI Case-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 6: Design Solution-3 E2E IPv4-Only PE-CE, Global
                    Table over IPv6-Only Core (4PE)

6.4.  IPv4-Only PE Design All SAFI Case-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 7: Design Solution-4 E2E IPv4-Only PE-CE, VPN over
                             IPv6-Only Core

6.5.  IPv4-Only PE Design All SAFI Case-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 8: Design Solution-5 E2E IPv4-Only PE-CE, Global
            Table over IPv4-Only Core (6PE) - Inter-AS Option-B

6.6.  IPv4-Only PE Design All SAFI Case-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 9: Design Solution-6 E2E IPv4-Only PE-CE, Global
            Table over IPv4-Only Core (6PE) - Inter-AS Option-C

6.7.  IPv4-Only PE Design All SAFI Case-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 10: Design Solution-7 E2E IPv4-Only PE-CE, VPN over
                     IPv4-Only Core - Inter-AS Option-B

6.8.  IPv4-Only PE Design All SAFI Case-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 11: Design Solution-8 E2E IPv4-Only PE-CE, VPN over
                     IPv4-Only Core - Inter-AS Option-C

6.9.  IPv4-Only PE Design All SAFI Case-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 12: Design Solution-9 E2E IPv4-Only PE-CE, Global
               Table over IPv6-Only Core - Inter-AS Option-B

6.10.  IPv4-Only PE Design All SAFI Case-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 13: Design Solution-10 E2E IPv4-Only PE-CE, Global
               Table over IPv6-Only Core - Inter-AS Option-C

6.11.  IPv4-Only PE Design All SAFI Case-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 14: Design Solution-11 E2E IPv4-Only PE-CE, VPN over
                     IPv6-Only Core - Inter-AS Option-B

6.12.  IPv4-Only PE Design All SAFI Case-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 15: Design Solution-12 E2E IPv4-Only PE-CE, VPN over
                     IPv6-Only Core - Inter-AS Option-C

7.  IPv6-Only PE Design ALL AFI/SFI Operational Considerations

   With a single IPv6 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.

   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 IPv6 transport peer carrying IPv4
   NLRI and IPv6 NLRI below:

   Physical interface is no longer dual stacked.

   Any change in IPv6 address or DAD state 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 IPv6 address
   family.



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

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

   From an operations perspective, prior to elimination of IPv4 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.

8.  IANA Considerations

   There are not any IANA considerations.

9.  Security Considerations

   The extensions defined in this document allow BGP to propagate
   reachability information about IPv4 prefixes over an MPLS or SR
   IPv6-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 IPv6 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].

10.  Acknowledgments

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

11.  Contributors

   The following people contributed substantive text to this document:

       Mohana Sundari
       EMail: mohanas@juniper.net


12.  References




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12.1.  Normative References

   [I-D.mishra-bess-ipv4-only-pe-design]
              Mishra, G. and J. Tantsura, "IPv4-Only PE Design for
              IPv6-NLRI with IPv4-NH", Work in Progress, Internet-Draft,
              draft-mishra-bess-ipv4-only-pe-design-01, 18 May 2022,
              <https://www.ietf.org/archive/id/draft-mishra-bess-ipv4-
              only-pe-design-01.txt>.

   [I-D.nalawade-kapoor-tunnel-safi]
              Nalawade, G., "BGP Tunnel SAFI", Work in Progress,
              Internet-Draft, draft-nalawade-kapoor-tunnel-safi-05, 29
              June 2006, <https://www.ietf.org/archive/id/draft-
              nalawade-kapoor-tunnel-safi-05.txt>.

   [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>.

   [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>.

   [RFC4761]  Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
              <https://www.rfc-editor.org/info/rfc4761>.

   [RFC5195]  Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP-Based
              Auto-Discovery for Layer-1 VPNs", RFC 5195,
              DOI 10.17487/RFC5195, June 2008,
              <https://www.rfc-editor.org/info/rfc5195>.




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   [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>.

   [RFC5747]  Wu, J., Cui, Y., Li, X., Xu, M., and C. Metz, "4over6
              Transit Solution Using IP Encapsulation and MP-BGP
              Extensions", RFC 5747, DOI 10.17487/RFC5747, March 2010,
              <https://www.rfc-editor.org/info/rfc5747>.

   [RFC6037]  Rosen, E., Ed., Cai, Y., Ed., and IJ. Wijnands, "Cisco
              Systems' Solution for Multicast in BGP/MPLS IP VPNs",
              RFC 6037, DOI 10.17487/RFC6037, October 2010,
              <https://www.rfc-editor.org/info/rfc6037>.

   [RFC7117]  Aggarwal, R., Ed., Kamite, Y., Fang, L., Rekhter, Y., and
              C. Kodeboniya, "Multicast in Virtual Private LAN Service
              (VPLS)", RFC 7117, DOI 10.17487/RFC7117, February 2014,
              <https://www.rfc-editor.org/info/rfc7117>.

   [RFC7267]  Martini, L., Ed., Bocci, M., Ed., and F. Balus, Ed.,
              "Dynamic Placement of Multi-Segment Pseudowires",
              RFC 7267, DOI 10.17487/RFC7267, June 2014,
              <https://www.rfc-editor.org/info/rfc7267>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [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>.

   [RFC8955]  Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
              Bacher, "Dissemination of Flow Specification Rules",
              RFC 8955, DOI 10.17487/RFC8955, December 2020,
              <https://www.rfc-editor.org/info/rfc8955>.




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   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

   [RFC9015]  Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
              Jalil, "BGP Control Plane for the Network Service Header
              in Service Function Chaining", RFC 9015,
              DOI 10.17487/RFC9015, June 2021,
              <https://www.rfc-editor.org/info/rfc9015>.

12.2.  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>.

   [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>.





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   [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


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











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