





Internet Engineering Task Force (IETF)                    W. George, Ed.
Request for Comments: 7439                             Time Warner Cable
Category: Informational                                C. Pignataro, Ed.
ISSN: 2070-1721                                                    Cisco
                                                            January 2015


           Gap Analysis for Operating IPv6-Only MPLS Networks

Abstract

   This document reviews the Multiprotocol Label Switching (MPLS)
   protocol suite in the context of IPv6 and identifies gaps that must
   be addressed in order to allow MPLS-related protocols and
   applications to be used with IPv6-only networks.  This document is
   intended to focus on gaps in the standards defining the MPLS suite,
   and is not intended to highlight particular vendor implementations
   (or lack thereof) in the context of IPv6-only MPLS functionality.

   In the data plane, MPLS fully supports IPv6, and MPLS labeled packets
   can be carried over IPv6 packets in a variety of encapsulations.
   However, support for IPv6 among MPLS control-plane protocols, MPLS
   applications, MPLS Operations, Administration, and Maintenance (OAM),
   and MIB modules is mixed, with some protocols having major gaps.  For
   most major gaps, work is in progress to upgrade the relevant
   protocols.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7439.









George & Pignataro            Informational                     [Page 1]

RFC 7439                     IPv6-Only MPLS                 January 2015


Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





































George & Pignataro            Informational                     [Page 2]

RFC 7439                     IPv6-Only MPLS                 January 2015


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Use Case  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Gap Analysis  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  MPLS Data Plane . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  MPLS Control Plane  . . . . . . . . . . . . . . . . . . .   6
       3.2.1.  Label Distribution Protocol (LDP) . . . . . . . . . .   6
       3.2.2.  Multipoint LDP (mLDP) . . . . . . . . . . . . . . . .   6
       3.2.3.  RSVP - Traffic Engineering (RSVP-TE)  . . . . . . . .   7
         3.2.3.1.  Interior Gateway Protocol (IGP) . . . . . . . . .   8
         3.2.3.2.  RSVP-TE Point-to-Multipoint (P2MP)  . . . . . . .   8
         3.2.3.3.  RSVP-TE Fast Reroute (FRR)  . . . . . . . . . . .   8
       3.2.4.  Path Computation Element (PCE)  . . . . . . . . . . .   8
       3.2.5.  Border Gateway Protocol (BGP) . . . . . . . . . . . .   9
       3.2.6.  Generalized Multi-Protocol Label Switching (GMPLS)  .   9
     3.3.  MPLS Applications . . . . . . . . . . . . . . . . . . . .   9
       3.3.1.  Layer 2 Virtual Private Network (L2VPN) . . . . . . .   9
         3.3.1.1.  Ethernet VPN (EVPN) . . . . . . . . . . . . . . .  10
       3.3.2.  Layer 3 Virtual Private Network (L3VPN) . . . . . . .  10
         3.3.2.1.  IPv6 Provider Edge/IPv4 Provider Edge (6PE/4PE) .  11
         3.3.2.2.  IPv6 Virtual Private Extension/IPv4 Virtual
                   Private Extension (6VPE/4VPE) . . . . . . . . . .  11
         3.3.2.3.  BGP Encapsulation Subsequent Address Family
                   Identifier (SAFI) . . . . . . . . . . . . . . . .  12
         3.3.2.4.  Multicast in MPLS/BGP IP VPN (MVPN) . . . . . . .  12
       3.3.3.  MPLS Transport Profile (MPLS-TP)  . . . . . . . . . .  13
     3.4.  MPLS Operations, Administration, and Maintenance (MPLS
           OAM)  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
       3.4.1.  Extended ICMP . . . . . . . . . . . . . . . . . . . .  14
       3.4.2.  Label Switched Path Ping (LSP Ping) . . . . . . . . .  15
       3.4.3.  Bidirectional Forwarding Detection (BFD)  . . . . . .  16
       3.4.4.  Pseudowire OAM  . . . . . . . . . . . . . . . . . . .  16
       3.4.5.  MPLS Transport Profile (MPLS-TP) OAM  . . . . . . . .  16
     3.5.  MIB Modules . . . . . . . . . . . . . . . . . . . . . . .  17
   4.  Gap Summary . . . . . . . . . . . . . . . . . . . . . . . . .  17
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  20
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  26
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28








George & Pignataro            Informational                     [Page 3]

RFC 7439                     IPv6-Only MPLS                 January 2015


1.  Introduction

   IPv6 [RFC2460] is an integral part of modern network deployments.  At
   the time when this document was written, the majority of these IPv6
   deployments were using dual-stack implementations, where IPv4 and
   IPv6 are supported equally on many or all of the network nodes, and
   single-stack primarily referred to IPv4-only devices.  Dual-stack
   deployments provide a useful margin for protocols and features that
   are not currently capable of operating solely over IPv6, because they
   can continue using IPv4 as necessary.  However, as IPv6 deployment
   and usage becomes more pervasive, and IPv4 exhaustion begins driving
   changes in address consumption behaviors, there is an increasing
   likelihood that many networks will need to start operating some or
   all of their network nodes either as primarily IPv6 (most functions
   use IPv6, a few legacy features use IPv4), or as IPv6-only (no IPv4
   provisioned on the device).  This transition toward IPv6-only
   operation exposes any gaps where features, protocols, or
   implementations are still reliant on IPv4 for proper function.  To
   that end, and in the spirit of the recommendation in RFC 6540
   [RFC6540] that implementations need to stop requiring IPv4 for proper
   and complete function, this document reviews the MPLS protocol suite
   in the context of IPv6 and identifies gaps that must be addressed in
   order to allow MPLS-related protocols and applications to be used
   with IPv6-only networks and networks that are primarily IPv6
   (hereafter referred to as IPv6-primary).  This document is intended
   to focus on gaps in the standards defining the MPLS suite, and not to
   highlight particular vendor implementations (or lack thereof) in the
   context of IPv6-only MPLS functionality.

2.  Use Case

   This section discusses some drivers for ensuring that MPLS completely
   supports IPv6-only operation.  It is not intended to be a
   comprehensive discussion of all potential use cases, but rather a
   discussion of one use case to provide context and justification to
   undertake such a gap analysis.

   IP convergence is continuing to drive new classes of devices to begin
   communicating via IP.  Examples of such devices could include set-top
   boxes for IP video distribution, cell tower electronics (macro or
   micro cells), infrastructure Wi-Fi access points, and devices for
   machine-to-machine (M2M) or Internet of Things (IoT) applications.
   In some cases, these classes of devices represent a very large
   deployment base, on the order of thousands or even millions of
   devices network-wide.  The scale of these networks, coupled with the
   increasingly overlapping use of RFC 1918 [RFC1918] address space
   within the average network and the lack of globally routable IPv4
   space available for long-term growth, begins to drive the need for



George & Pignataro            Informational                     [Page 4]

RFC 7439                     IPv6-Only MPLS                 January 2015


   many of the endpoints in this network to be managed solely via IPv6.
   Even if these devices are carrying some IPv4 user data, it is often
   encapsulated in another protocol such that the communication between
   the endpoint and its upstream devices can be IPv6-only without
   impacting support for IPv4 on user data.  As the number of devices to
   manage increases, the operator is compelled to move to IPv6.
   Depending on the MPLS features required, it is plausible to assume
   that the (existing) MPLS network will need to be extended to these
   IPv6-only devices.

   Additionally, as the impact of IPv4 exhaustion becomes more acute,
   more and more aggressive IPv4 address reclamation measures will be
   justified.  Many networks are likely to focus on preserving their
   remaining IPv4 addresses for revenue-generating customers so that
   legacy support for IPv4 can be maintained as long as necessary.  As a
   result, it may be appropriate for some or all of the network
   infrastructure, including MPLS Label Switching Routers (LSRs) and
   Label Edge Routers (LERs), to have its IPv4 addresses reclaimed and
   transition toward IPv6-only operation.

3.  Gap Analysis

   This gap analysis aims to answer the question of what fails when one
   attempts to use MPLS features on a network of IPv6-only devices.  The
   baseline assumption for this analysis is that some endpoints, as well
   as Label Switching Routers (Provider Edge (PE) and Provider (P)
   routers), only have IPv6 transport available and need to support the
   full suite of MPLS features defined as of the time of this document's
   writing at parity with the support on an IPv4 network.  This is
   necessary whether they are enabled via the Label Distribution
   Protocol (LDP) [RFC5036], RSVP - Traffic Engineering (RSVP-TE)
   [RFC3209], or Border Gateway Protocol (BGP) [RFC3107], and whether
   they are encapsulated in MPLS [RFC3032], IP [RFC4023], Generic
   Routing Encapsulation (GRE) [RFC4023], or Layer 2 Tunneling Protocol
   Version 3 (L2TPv3) [RFC4817].  It is important when evaluating these
   gaps to distinguish between user data and control-plane data, because
   while this document is focused on IPv6-only operation, it is quite
   likely that some amount of the user payload data being carried in the
   IPv6-only MPLS network will still be IPv4.

   A note about terminology: Gaps identified by this document are
   characterized as "Major" or "Minor".  Major gaps refer to significant
   changes necessary in one or more standards to address the gap due to
   existing standards language having either missing functionality for
   IPv6-only operation or explicit language requiring the use of IPv4
   with no IPv6 alternatives defined.  Minor gaps refer to changes
   necessary primarily to clarify existing standards language.  Usually




George & Pignataro            Informational                     [Page 5]

RFC 7439                     IPv6-Only MPLS                 January 2015


   these changes are needed in order to explicitly codify IPv6 support
   in places where it is either implicit or omitted today, but the
   omission is unlikely to prevent IPv6-only operation.

3.1.  MPLS Data Plane

   MPLS labeled packets can be transmitted over a variety of data links
   [RFC3032], and MPLS labeled packets can also be encapsulated over IP.
   The encapsulations of MPLS in IP and GRE, as well as MPLS over
   L2TPv3, support IPv6.  See Section 3 of RFC 4023 [RFC4023] and
   Section 2 of RFC 4817 [RFC4817], respectively.

   Gap: None.

3.2.  MPLS Control Plane

3.2.1.  Label Distribution Protocol (LDP)

   The Label Distribution Protocol (LDP) [RFC5036] defines a set of
   procedures for distribution of labels between Label Switching Routers
   that can use the labels for forwarding traffic.  While LDP was
   designed to use an IPv4 or dual-stack IP network, it has a number of
   deficiencies that prevent it from working in an IPv6-only network.
   LDP-IPv6 [LDP-IPv6] highlights some of the deficiencies when LDP is
   enabled in IPv6-only or dual-stack networks and specifies appropriate
   protocol changes.  These deficiencies are related to Label Switched
   Path (LSP) mapping, LDP identifiers, LDP discovery, LDP session
   establishment, next-hop address, and LDP Time To Live (TTL) security
   [RFC5082] [RFC6720].

   Gap: Major; update to RFC 5036 in progress via [LDP-IPv6], which
   should close this gap.

3.2.2.  Multipoint LDP (mLDP)

   Multipoint LDP (mLDP) is a set of extensions to LDP for setting up
   Point-to-Multipoint (P2MP) and Multipoint-to-Multipoint (MP2MP) LSPs.
   These extensions are specified in RFC 6388 [RFC6388].  In terms of
   IPv6-only gap analysis, mLDP has two identified areas of interest:

   1.  LDP Control Plane: Since mLDP uses the LDP control plane to
       discover and establish sessions with the peer, it shares the same
       gaps as LDP (Section 3.2.1) with regards to control plane
       (discovery, transport, and session establishment) in an IPv6-only
       network.






George & Pignataro            Informational                     [Page 6]

RFC 7439                     IPv6-Only MPLS                 January 2015


   2.  Multipoint (MP) Forwarding Equivalence Class (FEC) Root Address:
       mLDP defines its own MP FECs and rules, different from LDP, to
       map MP LSPs.  An mLDP MP FEC contains a Root Address field that
       is an IP address in IP networks.  The current specification
       allows specifying the root address according to the Address
       Family Identifier (AFI), and hence covers both IPv4 or IPv6 root
       addresses, requiring no extension to support IPv6-only MP LSPs.
       The root address is used by each LSR participating in an MP LSP
       setup such that root address reachability is resolved by doing a
       table lookup against the root address to find corresponding
       upstream neighbor(s).  This will pose a problem if an MP LSP
       traverses IPv4-only and IPv6-only nodes in a dual-stack network
       on the way to the root node.

   For example, consider following setup, where R1/R6 are IPv4-only, R3/
   R4 are IPv6-only, and R2/R5 are dual-stack LSRs:

   ( IPv4-only )  (  IPv6-only   )  ( IPv4-only )
          R1 -- R2 -- R3 -- R4 -- R5 -- R6
          Leaf                          Root

   Assume R1 to be a leaf node for a P2MP LSP rooted at R6 (root node).
   R1 uses R6's IPv4 address as the root address in MP FEC.  As the MP
   LSP signaling proceeds from R1 to R6, the MP LSP setup will fail on
   the first IPv6-only transit/branch LSRs (R3) when trying to find IPv4
   root address reachability.  RFC 6512 [RFC6512] defines a recursive-
   FEC solution and procedures for mLDP when the backbone (transit/
   branch) LSRs have no route to the root.  The proposed solution is
   defined for a BGP-free core in a VPN environment, but a similar
   concept can be used/extended to solve the above issue of the
   IPv6-only backbone receiving an MP FEC element with an IPv4 address.
   The solution will require a border LSR (the one that is sitting on
   the border of an IPv4/IPv6 island (namely, R2 and R5 in this
   example)) to translate an IPv4 root address to an equivalent IPv6
   address (and vice versa) through procedures similar to RFC 6512.

   Gap: Major; update in progress for LDP via [LDP-IPv6], may need
   additional updates to RFC 6512.

3.2.3.  RSVP - Traffic Engineering (RSVP-TE)

   RSVP-TE [RFC3209] defines a set of procedures and enhancements to
   establish LSP tunnels that can be automatically routed away from
   network failures, congestion, and bottlenecks.  RSVP-TE allows
   establishing an LSP for an IPv4 or IPv6 prefix, thanks to its
   LSP_TUNNEL_IPv6 object and subobjects.

   Gap: None.



George & Pignataro            Informational                     [Page 7]

RFC 7439                     IPv6-Only MPLS                 January 2015


3.2.3.1.  Interior Gateway Protocol (IGP)

   RFC 3630 [RFC3630] specifies a method of adding traffic engineering
   capabilities to OSPF Version 2.  New TLVs and sub-TLVs were added in
   RFC 5329 [RFC5329] to extend TE capabilities to IPv6 networks in OSPF
   Version 3.

   RFC 5305 [RFC5305] specifies a method of adding traffic engineering
   capabilities to IS-IS.  New TLVs and sub-TLVs were added in RFC 6119
   [RFC6119] to extend TE capabilities to IPv6 networks.

   Gap: None.

3.2.3.2.  RSVP-TE Point-to-Multipoint (P2MP)

   RFC 4875 [RFC4875] describes extensions to RSVP-TE for the setup of
   Point-to-Multipoint (P2MP) LSPs in MPLS and Generalized MPLS (GMPLS)
   with support for both IPv4 and IPv6.

   Gap: None.

3.2.3.3.  RSVP-TE Fast Reroute (FRR)

   RFC 4090 [RFC4090] specifies Fast Reroute (FRR) mechanisms to
   establish backup LSP tunnels for local repair supporting both IPv4
   and IPv6 networks.  Further, [RFC5286] describes the use of loop-free
   alternates to provide local protection for unicast traffic in pure IP
   and MPLS networks in the event of a single failure, whether link,
   node, or shared risk link group (SRLG) for both IPv4 and IPv6.

   Gap: None.

3.2.4.  Path Computation Element (PCE)

   The Path Computation Element (PCE) defined in RFC 4655 [RFC4655] is
   an entity that is capable of computing a network path or route based
   on a network graph and applying computational constraints.  A Path
   Computation Client (PCC) may make requests to a PCE for paths to be
   computed.  The PCE Communication Protocol (PCEP) is designed as a
   communication protocol between PCCs and PCEs for path computations
   and is defined in RFC 5440 [RFC5440].

   The PCEP specification [RFC5440] is defined for both IPv4 and IPv6
   with support for PCE discovery via an IGP (OSPF [RFC5088] or IS-IS
   [RFC5089]) using both IPv4 and IPv6 addresses.  Note that PCEP uses
   identical encoding of subobjects, as in RSVP-TE defined in RFC 3209
   [RFC3209] that supports both IPv4 and IPv6.




George & Pignataro            Informational                     [Page 8]

RFC 7439                     IPv6-Only MPLS                 January 2015


   The extensions to PCEP to support confidentiality [RFC5520], route
   exclusions [RFC5521], monitoring [RFC5886], and P2MP TE LSPs
   [RFC6006] have support for both IPv4 and IPv6.

   Gap: None.

3.2.5.  Border Gateway Protocol (BGP)

   RFC 3107 [RFC3107] specifies a set of BGP protocol procedures for
   distributing the labels (for prefixes corresponding to any address
   family) between label switch routers so that they can use the labels
   for forwarding the traffic.  RFC 3107 allows BGP to distribute the
   label for IPv4 or IPv6 prefix in an IPv6-only network.

   Gap: None.

3.2.6.  Generalized Multi-Protocol Label Switching (GMPLS)

   The Generalized Multi-Protocol Label Switching (GMPLS) specification
   includes signaling functional extensions [RFC3471] and RSVP-TE
   extensions [RFC3473].  The gap analysis in Section 3.2.3 applies to
   these.

   RFC 4558 [RFC4558] specifies Node-ID Based RSVP Hello Messages with
   capability for both IPv4 and IPv6.  RFC 4990 [RFC4990] clarifies the
   use of IPv6 addresses in GMPLS networks including handling in the MIB
   modules.

   The second paragraph of Section 5.3 of RFC 6370 [RFC6370] describes
   the mapping from an MPLS Transport Profile (MPLS-TP) LSP_ID to RSVP-
   TE with an assumption that Node_IDs are derived from valid IPv4
   addresses.  This assumption fails in an IPv6-only network, given that
   there would not be any IPv4 addresses.

   Gap: Minor; Section 5.3 of RFC 6370 [RFC6370] needs to be updated.

3.3.  MPLS Applications

3.3.1.  Layer 2 Virtual Private Network (L2VPN)

   L2VPN [RFC4664] specifies two fundamentally different kinds of Layer
   2 VPN services that a service provider could offer to a customer:
   Virtual Private Wire Service (VPWS) and Virtual Private LAN Service
   (VPLS).  RFC 4447 [RFC4447] and RFC 4762 [RFC4762] specify the LDP
   protocol changes to instantiate VPWS and VPLS services, respectively,
   in an MPLS network using LDP as the signaling protocol.  This is
   complemented by RFC 6074 [RFC6074], which specifies a set of
   procedures for instantiating L2VPNs (e.g., VPWS, VPLS) using BGP as a



George & Pignataro            Informational                     [Page 9]

RFC 7439                     IPv6-Only MPLS                 January 2015


   discovery protocol and LDP, as well as L2TPv3, as a signaling
   protocol.  RFC 4761 [RFC4761] and RFC 6624 [RFC6624] specify BGP
   protocol changes to instantiate VPLS and VPWS services in an MPLS
   network, using BGP for both discovery and signaling.

   In an IPv6-only MPLS network, use of L2VPN represents a connection of
   Layer 2 islands over an IPv6 MPLS core, and very few changes are
   necessary to support operation over an IPv6-only network.  The L2VPN
   signaling protocol is either BGP or LDP in an MPLS network, and both
   can run directly over IPv6 core infrastructure as well as IPv6 edge
   devices.  RFC 6074 [RFC6074] is the only RFC that appears to have a
   gap for IPv6-only operation.  In its discovery procedures (Sections
   3.2.2 and 6 of RFC 6074 [RFC6074]), it suggests encoding PE IP
   addresses in the Virtual Switching Instance ID (VSI-ID), which is
   encoded in Network Layer Reachability Information (NLRI) and should
   not exceed 12 bytes (to differentiate its AFI/SAFI (Subsequent
   Address Family Identifier) encoding from RFC 4761).  This means that
   a PE IP address cannot be an IPv6 address.  Also, in its signaling
   procedures (Section 3.2.3 of RFC 6074 [RFC6074]), it suggests
   encoding PE_addr in the Source Attachment Individual Identifier
   (SAII) and the Target Attachment Individual Identifier (TAII), which
   are limited to 32 bits (AII Type=1) at the moment.

   RFC 6073 [RFC6073] defines the new LDP Pseudowire (PW) Switching
   Point PE TLV, which supports IPv4 and IPv6.

   Gap: Minor; RFC 6074 needs to be updated.

3.3.1.1.  Ethernet VPN (EVPN)

   Ethernet VPN [EVPN] defines a method for using BGP MPLS-based
   Ethernet VPNs.  Because it can use functions in LDP and mLDP, as well
   as Multicast VPLS [RFC7117], it inherits LDP gaps previously
   identified in Section 3.2.1.  Once those gaps are resolved, it should
   function properly on IPv6-only networks as defined.

   Gap: Major for LDP; update to RFC 5036 in progress via [LDP-IPv6]
   that should close this gap (see Section 3.2.1).

3.3.2.  Layer 3 Virtual Private Network (L3VPN)

   RFC 4364 [RFC4364] defines a method by which a Service Provider may
   use an IP backbone to provide IP VPNs for its customers.  The
   following use cases arise in the context of this gap analysis:

   1.  Connecting IPv6 islands over IPv6-only MPLS network

   2.  Connecting IPv4 islands over IPv6-only MPLS network



George & Pignataro            Informational                    [Page 10]

RFC 7439                     IPv6-Only MPLS                 January 2015


   Both use cases require mapping an IP packet to an IPv6-signaled LSP.
   RFC 4364 defines Layer 3 Virtual Private Networks (L3VPNs) for
   IPv4-only and has references to 32-bit BGP next-hop addresses.  RFC
   4659 [RFC4659] adds support for IPv6 on L3VPNs, including 128-bit BGP
   next-hop addresses, and discusses operation whether IPv6 is the
   payload or the underlying transport address family.  However, RFC
   4659 does not formally update RFC 4364, and thus an implementer may
   miss this additional set of standards unless it is explicitly
   identified independently of the base functionality defined in RFC
   4364.  Further, Section 1 of RFC 4659 explicitly identifies use case
   2 as out of scope for the document.

   The authors do not believe that there are any additional issues
   encountered when using L2TPv3, RSVP, or GRE (instead of MPLS) as
   transport on an IPv6-only network.

   Gap: Major; RFC 4659 needs to be updated to explicitly cover use case
   2 (discussed in further detail below)

3.3.2.1.  IPv6 Provider Edge/IPv4 Provider Edge (6PE/4PE)

   RFC 4798 [RFC4798] defines IPv6 Provider Edge (6PE), which defines
   how to interconnect IPv6 islands over a MPLS-enabled IPv4 cloud.
   However, use case 2 is doing the opposite, and thus could also be
   referred to as IPv4 Provider Edge (4PE).  The method to support this
   use case is not defined explicitly.  To support it, IPv4 edge devices
   need to be able to map IPv4 traffic to MPLS IPv6 core LSPs.  Also,
   the core switches may not understand IPv4 at all, but in some cases
   they may need to be able to exchange Labeled IPv4 routes from one
   Autonomous System (AS) to a neighboring AS.

   Gap: Major; RFC 4798 covers only the "6PE" case.  Use case 2 is
   currently not specified in an RFC.

3.3.2.2.  IPv6 Virtual Private Extension/IPv4 Virtual Private Extension
          (6VPE/4VPE)

   RFC 4659 [RFC4659] defines IPv6 Virtual Private Network Extension
   (6VPE), a method by which a Service Provider may use its packet-
   switched backbone to provide Virtual Private Network (VPN) services
   for its IPv6 customers.  It allows the core network to be MPLS IPv4
   or MPLS IPv6, thus addressing use case 1 above.  RFC 4364 should work
   as defined for use case 2 above, which could also be referred to as
   IPv4 Virtual Private Extension (4VPE), but the RFC explicitly does
   not discuss this use and defines it as out of scope.

   Gap: Minor; RFC 4659 needs to be updated to explicitly cover use case
   2.



George & Pignataro            Informational                    [Page 11]

RFC 7439                     IPv6-Only MPLS                 January 2015


3.3.2.3.  BGP Encapsulation Subsequent Address Family Identifier (SAFI)

   RFC 5512 [RFC5512] defines the BGP Encapsulation SAFI and the BGP
   Tunnel Encapsulation Attribute, which can be used to signal tunneling
   over an IP Core that is using a single address family.  This
   mechanism supports transport of MPLS (and other protocols) over
   Tunnels in an IP core (including an IPv6-only core).  In this
   context, load balancing can be provided as specified in RFC 5640
   [RFC5640].

   Gap: None.

3.3.2.4.  Multicast in MPLS/BGP IP VPN (MVPN)

   RFC 6513 [RFC6513] defines the procedure to provide multicast service
   over an MPLS VPN backbone for downstream customers.  It is sometimes
   referred to as Next Generation Multicast VPN (NG-MVPN) The procedure
   involves the below set of protocols.

3.3.2.4.1.  PE-CE Multicast Routing Protocol

   RFC 6513 [RFC6513] explains the use of Protocol Independent Multicast
   (PIM) as a Provider Edge - Customer Edge (PE-CE) protocol, while
   Section 11.1.2 of RFC 6514 [RFC6514] explains the use of mLDP as a
   PE-CE protocol.

   The MCAST-VPN NLRI route-type format defined in RFC 6514 [RFC6514] is
   not sufficiently covering all scenarios when mLDP is used as a PE-CE
   protocol.  The issue is explained in Section 2 of [mLDP-NLRI] along
   with a new route type that encodes the mLDP FEC in NLRI.

   Further, [PE-CE] defines the use of BGP as a PE-CE protocol.

   Gap: None.

3.3.2.4.2.  P-Tunnel Instantiation

   [RFC6513] explains the use of the below tunnels:

   o  RSVP-TE P2MP LSP

   o  PIM Tree

   o  mLDP P2MP LSP

   o  mLDP MP2MP LSP

   o  Ingress Replication



George & Pignataro            Informational                    [Page 12]

RFC 7439                     IPv6-Only MPLS                 January 2015


   Gap: Gaps in RSVP-TE P2MP LSP (Section 3.2.3.2) and mLDP
   (Section 3.2.2) P2MP and MP2MP LSP are covered in previous sections.
   There are no MPLS-specific gaps for PIM Tree or Ingress Replication,
   and any protocol-specific gaps not related to MPLS are outside the
   scope of this document.

3.3.2.4.3.  PE-PE Multicast Routing Protocol

   Section 3.1 of RFC 6513 [RFC6513] explains the use of PIM as a PE-PE
   protocol, while RFC 6514 [RFC6514] explains the use of BGP as a PE-PE
   protocol.

   PE-PE multicast routing is not specific to P-tunnels or to MPLS.  It
   can be PIM or BGP with P-tunnels that are label based or PIM tree
   based.  Enabling PIM as a PE-PE multicast protocol is equivalent to
   running it on a non-MPLS IPv6 network, so there are not any MPLS-
   specific considerations and any gaps are applicable for non-MPLS
   networks as well.  Similarly, BGP only includes the P-Multicast
   Service Interface (PMSI) tunnel attribute as a part of the NLRI,
   which is inherited from P-tunnel instantiation and considered to be
   an opaque value.  Any gaps in the control plane (PIM or BGP) will not
   be specific to MPLS.

   Gap: Any gaps in PIM or BGP as a PE-PE multicast routing protocol are
   not unique to MPLS, and therefore are outside the scope of this
   document.  It is included for completeness.

3.3.3.  MPLS Transport Profile (MPLS-TP)

   MPLS-TP does not require IP (see Section 2 of RFC 5921 [RFC5921]) and
   should not be affected by operation on an IPv6-only network.
   Therefore, this is considered out of scope for this document but is
   included for completeness.

   Although not required, MPLS-TP can use IP.  One such example is
   included in Section 3.2.6, where MPLS-TP identifiers can be derived
   from valid IPv4 addresses.

   Gap: None.  MPLS-TP does not require IP.

3.4.  MPLS Operations, Administration, and Maintenance (MPLS OAM)

   For MPLS LSPs, there are primarily three OAM mechanisms: Extended
   ICMP [RFC4884] [RFC4950], LSP Ping [RFC4379], and Bidirectional
   Forwarding Detection (BFD) for MPLS LSPs [RFC5884].  For MPLS
   Pseudowires, there is also Virtual Circuit Connectivity Verification
   (VCCV) [RFC5085] [RFC5885].  Most of these mechanisms work in pure




George & Pignataro            Informational                    [Page 13]

RFC 7439                     IPv6-Only MPLS                 January 2015


   IPv6 environments, but there are some problems encountered in mixed
   environments due to address-family mismatches.  The next subsections
   cover these gaps in detail.

   Gap: Major; RFC 4379 needs to be updated to better support multipath
   IPv6.  Additionally, there is potential for dropped messages in
   Extended ICMP and LSP Ping due to IP version mismatches.  It is
   important to note that this is a more generic problem with tunneling
   when address-family mismatches exist and is not specific to MPLS.
   While MPLS will be affected, it will be difficult to fix this problem
   specifically for MPLS, rather than fixing the more generic problem.

3.4.1.  Extended ICMP

   Extended ICMP to support Multi-part messages is defined in RFC 4884
   [RFC4884].  This extensibility is defined generally for both ICMPv4
   and ICMPv6.  The specific ICMP extensions for MPLS are defined in RFC
   4950 [RFC4950].  ICMP Multi-part with MPLS extensions works for IPv4
   and IPv6.  However, the mechanisms described in RFC 4884 and 4950 may
   fail when tunneling IPv4 traffic over an LSP that is supported by an
   IPv6-only infrastructure.

   Assume the following:

   o  The path between two IPv4-only hosts contains an MPLS LSP.

   o  The two routers that terminate the LSP run dual stack.

   o  The LSP interior routers run IPv6 only.

   o  The LSP is signaled over IPv6.

   Now assume that one of the hosts sends an IPv4 packet to the other.
   However, the packet's TTL expires on an LSP interior router.
   According to RFC 3032 [RFC3032], the interior router should examine
   the IPv4 payload, format an ICMPv4 message, and send it (over the
   tunnel upon which the original packet arrived) to the egress LSP.  In
   this case, however, the LSP interior router is not IPv4-aware.  It
   cannot parse the original IPv4 datagram, nor can it send an IPv4
   message.  So, no ICMP message is delivered to the source.  Some
   specific ICMP extensions, in particular, ICMP extensions for
   interface and next-hop identification [RFC5837], restrict the address
   family of address information included in an Interface Information
   Object to the same one as the ICMP (see Section 4.5 of RFC 5837).
   While these extensions are not MPLS specific, they can be used with
   MPLS packets carrying IP datagrams.  This has no implications for
   IPv6-only environments.




George & Pignataro            Informational                    [Page 14]

RFC 7439                     IPv6-Only MPLS                 January 2015


   Gap: Major; IP version mismatches may cause dropped messages.
   However, as noted in the previous section, this problem is not
   specific to MPLS.

3.4.2.  Label Switched Path Ping (LSP Ping)

   The LSP Ping mechanism defined in RFC 4379 [RFC4379] is specified to
   work with IPv6.  Specifically, the Target FEC Stacks include both
   IPv4 and IPv6 versions of all FECs (see Section 3.2 of RFC 4379).
   The only exceptions are the Pseudowire FECs, which are later
   specified for IPv6 in RFC 6829 [RFC6829].  The multipath information
   also includes IPv6 encodings (see Section 3.3.1 of RFC 4379).

   LSP Ping packets are UDP packets over either IPv4 or IPv6 (see
   Section 4.3 of RFC 4379).  However, for IPv6 the destination IP
   address is a (randomly chosen) IPv6 address from the range
   0:0:0:0:0:FFFF:127/104; that is, using an IPv4-mapped IPv6 address.
   This is a transitional mechanism that should not bleed into IPv6-only
   networks, as [IPv4-MAPPED] explains.  The issue is that the MPLS LSP
   Ping mechanism needs a range of loopback IP addresses to be used as
   destination addresses to exercise Equal Cost Multiple Path (ECMP),
   but the IPv6 address architecture specifies a single address
   (::1/128) for loopback.  A mechanism to achieve this was proposed in
   [LOOPBACK-PREFIX].

   Additionally, RFC 4379 does not define the value to be used in the
   IPv6 Router Alert option (RAO).  For IPv4 RAO, a value of zero is
   used.  However, there is no equivalent value for IPv6 RAO.  This gap
   needs to be fixed to be able to use LSP Ping in IPv6 networks.
   Further details on this gap are captured, along with a proposed
   solution, in [IPv6-RAO].

   Another gap is that the mechanisms described in RFC 4379 may fail
   when tunneling IPv4 traffic over an LSP that is supported by
   IPv6-only infrastructure.

   Assume the following:

   o  LSP Ping is operating in traceroute mode over an MPLS LSP.

   o  The two routers that terminate the LSP run dual stack.

   o  The LSP interior routers run IPv6 only.

   o  The LSP is signaled over IPv6.






George & Pignataro            Informational                    [Page 15]

RFC 7439                     IPv6-Only MPLS                 January 2015


   Packets will expire at LSP interior routers.  According to RFC 4379,
   the interior router must parse the IPv4 Echo Request and then send an
   IPv4 Echo Reply.  However, the LSP interior router is not IPv4-aware.
   It cannot parse the IPv4 Echo Request, nor can it send an IPv4 Echo
   Reply.  So, no reply is sent.

   The mechanism described in RFC 4379 also does not sufficiently
   explain the behavior in certain IPv6-specific scenarios.  For
   example, RFC 4379 defines the K value as 28 octets when the Address
   Family is set to IPv6 Unnumbered, but it doesn't describe how to
   carry a 32-bit LSR Router ID in the 128-bit Downstream IP Address
   field.

   Gap: Major; LSP Ping uses IPv4-mapped IPv6 addresses.  IP version
   mismatches may cause dropped messages and unclear mapping from the
   LSR Router ID to Downstream IP Address.

3.4.3.  Bidirectional Forwarding Detection (BFD)

   The BFD specification for MPLS LSPs [RFC5884] is defined for IPv4, as
   well as IPv6, versions of MPLS FECs (see Section 3.1 of RFC 5884).
   Additionally, the BFD packet is encapsulated over UDP and specified
   to run over both IPv4 and IPv6 (see Section 7 of RFC 5884).

   Gap: None.

3.4.4.  Pseudowire OAM

   The OAM specifications for MPLS Pseudowires define usage for both
   IPv4 and IPv6.  Specifically, VCCV [RFC5085] can carry IPv4 or IPv6
   OAM packets (see Sections 5.1.1 and 5.2.1 of RFC 5085), and VCCV for
   BFD [RFC5885] also defines an IPv6 encapsulation (see Section 3.2 of
   RFC 5885).

   Additionally, for LSP Ping for pseudowires, the Pseudowire FECs are
   specified for IPv6 in RFC 6829 [RFC6829].

   Gap: None.

3.4.5.  MPLS Transport Profile (MPLS-TP) OAM

   As with MPLS-TP, MPLS-TP OAM [RFC6371] does not require IP or
   existing MPLS OAM functions and should not be affected by operation
   on an IPv6-only network.  Therefore, this is out of scope for this
   document but is included for completeness.  Although not required,
   MPLS-TP can use IP.

   Gap: None.  MPLS-TP OAM does not require IP.



George & Pignataro            Informational                    [Page 16]

RFC 7439                     IPv6-Only MPLS                 January 2015


3.5.  MIB Modules

   RFC 3811 [RFC3811] defines the textual conventions for MPLS.  These
   lack support for IPv6 in defining MplsExtendedTunnelId and
   MplsLsrIdentifier.  These textual conventions are used in the MPLS-TE
   MIB specification [RFC3812], the GMPLS-TE MIB specification [RFC4802]
   and the FRR extension [RFC6445].  "Definitions of Textual Conventions
   (TCs) for Multiprotocol Label Switching (MPLS) Management" [MPLS-TC]
   tries to resolve this gap by marking this textual convention as
   obsolete.

   The other MIB specifications for LSR [RFC3813], LDP [RFC3815], and TE
   [RFC4220] have support for both IPv4 and IPv6.

   Lastly, RFC 4990 [RFC4990] discusses how to handle IPv6 sources and
   destinations in the MPLS and GMPLS-TE MIB modules.  In particular,
   Section 8 of RFC 4990 [RFC4990] describes a method of defining or
   monitoring an LSP tunnel using the MPLS-TE and GMPLS-TE MIB modules,
   working around some of the limitations in RFC 3811 [RFC3811].

   Gap: Minor; Section 8 of RFC 4990 [RFC4990] describes a method to
   handle IPv6 addresses in the MPLS-TE [RFC3812] and GMPLS-TE [RFC4802]
   MIB modules.  Work underway to update RFC 3811 via [MPLS-TC], may
   also need to update RFC 3812, RFC 4802, and RFC 6445, which depend on
   it.

4.  Gap Summary

   This document has reviewed a wide variety of MPLS features and
   protocols to determine their suitability for use on IPv6-only or
   IPv6-primary networks.  While some parts of the MPLS suite will
   function properly without additional changes, gaps have been
   identified in others that will need to be addressed with follow-on
   work.  This section will summarize those gaps, along with pointers to
   any work in progress to address them.  Note that because the
   referenced documents are works in progress and do not have consensus
   at the time of this document's publication, there could be other
   solutions proposed at a future time, and the pointers in this
   document should not be considered normative in any way.
   Additionally, work in progress on new features that use MPLS
   protocols will need to ensure that those protocols support operation
   on IPv6-only or IPv6-primary networks, or explicitly identify any
   dependencies on existing gaps that, once resolved, will allow proper
   IPv6-only operation.







George & Pignataro            Informational                    [Page 17]

RFC 7439                     IPv6-Only MPLS                 January 2015


              Identified Gaps in MPLS for IPv6-Only Networks

   +---------+---------------------------------------+-----------------+
   |   Item  |                  Gap                  |   Addressed in  |
   +---------+---------------------------------------+-----------------+
   |   LDP   |   LSP mapping, LDP identifiers, LDP   |    [LDP-IPv6]   |
   | S.3.2.1 | discovery, LDP session establishment, |                 |
   |         |     next-hop address, and LDP TTL     |                 |
   |         |                security               |                 |
   +---------+---------------------------------------+-----------------+
   |   mLDP  |    Inherits gaps from LDP, RFC 6512   |     Inherits    |
   | S.3.2.2 |               [RFC6512]               |   [LDP-IPv6],   |
   |         |                                       |    additional   |
   |         |                                       |    fixes TBD    |
   +---------+---------------------------------------+-----------------+
   |  GMPLS  | RFC 6370 [RFC6370] Node ID derivation |       TBD       |
   | S.3.2.6 |                                       |                 |
   +---------+---------------------------------------+-----------------+
   |  L2VPN  |     RFC 6074 [RFC6074] discovery,     |       TBD       |
   | S.3.3.1 |               signaling               |                 |
   +---------+---------------------------------------+-----------------+
   |  L3VPN  |  RFC 4659 [RFC4659] does not define a |       TBD       |
   | S.3.3.2 |          method for 4PE/4VPE          |                 |
   +---------+---------------------------------------+-----------------+
   |   OAM   |  RFC 4379 [RFC4379] No IPv6 multipath |    [IPv6-RAO]   |
   |  S.3.4  |     support, no IPv6 RAO, possible    |                 |
   |         |     dropped messages in IP version    |                 |
   |         |                mismatch               |                 |
   +---------+---------------------------------------+-----------------+
   |   MIB   |   RFC 3811 [RFC3811] no IPv6 textual  |    [MPLS-TC]    |
   | Modules |               convention              |                 |
   |  S.3.5  |                                       |                 |
   +---------+---------------------------------------+-----------------+

                       Table 1: IPv6-Only MPLS Gaps

5.  Security Considerations

   Changing the address family used for MPLS network operation does not
   fundamentally alter the security considerations currently extant in
   any of the specifics of the protocol or its features.  However,
   follow-on work recommended by this gap analysis will need to address
   any effects that the use of IPv6 in their modifications may have on
   security.







George & Pignataro            Informational                    [Page 18]

RFC 7439                     IPv6-Only MPLS                 January 2015


6.  References

6.1.  Normative References

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998,
              <http://www.rfc-editor.org/info/rfc2460>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, January 2001,
              <http://www.rfc-editor.org/info/rfc3032>.

   [RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in
              BGP-4", RFC 3107, May 2001,
              <http://www.rfc-editor.org/info/rfc3107>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001,
              <http://www.rfc-editor.org/info/rfc3209>.

   [RFC3471]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Functional Description", RFC 3471,
              January 2003, <http://www.rfc-editor.org/info/rfc3471>.

   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE) Extensions", RFC 3473, January 2003,
              <http://www.rfc-editor.org/info/rfc3473>.

   [RFC3811]  Nadeau, T. and J. Cucchiara, "Definitions of Textual
              Conventions (TCs) for Multiprotocol Label Switching (MPLS)
              Management", RFC 3811, June 2004,
              <http://www.rfc-editor.org/info/rfc3811>.

   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating
              MPLS in IP or Generic Routing Encapsulation (GRE)", RFC
              4023, March 2005,
              <http://www.rfc-editor.org/info/rfc4023>.

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006, <http://www.rfc-editor.org/info/rfc4379>.







George & Pignataro            Informational                    [Page 19]

RFC 7439                     IPv6-Only MPLS                 January 2015


   [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, September 2006,
              <http://www.rfc-editor.org/info/4659>.

   [RFC4817]  Townsley, M., Pignataro, C., Wainner, S., Seely, T., and
              J. Young, "Encapsulation of MPLS over Layer 2 Tunneling
              Protocol Version 3", RFC 4817, March 2007,
              <http://www.rfc-editor.org/info/rfc4817>.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007,
              <http://www.rfc-editor.org/info/rfc5036>.

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

   [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
              Profile (MPLS-TP) Identifiers", RFC 6370, September 2011,
              <http://www.rfc-editor.org/info/rfc6370>.

   [RFC6512]  Wijnands, IJ., Rosen, E., Napierala, M., and N. Leymann,
              "Using Multipoint LDP When the Backbone Has No Route to
              the Root", RFC 6512, February 2012,
              <http://www.rfc-editor.org/info/rfc6512>.

6.2.  Informative References

   [EVPN]     Sajassi, A., Aggarwal, R., Bitar, N., Isaac, A., and J.
              Uttaro, "BGP MPLS Based Ethernet VPN", Work in Progress,
              draft-ietf-l2vpn-evpn-11, October 2014.

   [IPv4-MAPPED]
              Metz, C. and J. Hagino, "IPv4-Mapped Addresses on the Wire
              Considered Harmful", Work in Progress, draft-itojun-v6ops-
              v4mapped-harmful-02, October 2003.

   [IPv6-RAO]
              Raza, K., Akiya, N., and C. Pignataro, "IPv6 Router Alert
              Option for MPLS OAM", Work in Progress, draft-raza-mpls-
              oam-ipv6-rao-02, September 2014.

   [LDP-IPv6]
              Asati, R., Manral, V., Papneja, R., and C. Pignataro,
              "Updates to LDP for IPv6", Work in Progress, draft-ietf-
              mpls-ldp-ipv6-14, October 2014.



George & Pignataro            Informational                    [Page 20]

RFC 7439                     IPv6-Only MPLS                 January 2015


   [LOOPBACK-PREFIX]
              Smith, M., "A Larger Loopback Prefix for IPv6", Work in
              Progress, draft-smith-v6ops-larger-ipv6-loopback-prefix-
              04, February 2013.

   [mLDP-NLRI]
              Wijnands, I., Rosen, E., and U. Joorde, "Encoding mLDP
              FECs in the NLRI of BGP MCAST-VPN Routes", Work in
              Progress, draft-ietf-l3vpn-mvpn-mldp-nlri-10, November
              2014.

   [MPLS-TC]  Manral, V., Tsou, T., Will, W., and F. Fondelli,
              "Definitions of Textual Conventions (TCs) for
              Multiprotocol Label Switching (MPLS) Management", Work in
              Progress, draft-manral-mpls-rfc3811bis-04, September 2014.

   [PE-CE]    Patel, K., Rekhter, Y., and E. Rosen, "BGP as an MVPN
              PE-CE Protocol", Work in Progress,
              draft-ietf-l3vpn-mvpn-pe- ce-02, October 2014.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996,
              <http://www.rfc-editor.org/info/rfc1918>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630, September
              2003, <http://www.rfc-editor.org/info/rfc3630>.

   [RFC3812]  Srinivasan, C., Viswanathan, A., and T. Nadeau,
              "Multiprotocol Label Switching (MPLS) Traffic Engineering
              (TE) Management Information Base (MIB)", RFC 3812, June
              2004, <http://www.rfc-editor.org/info/rfc3812>.

   [RFC3813]  Srinivasan, C., Viswanathan, A., and T. Nadeau,
              "Multiprotocol Label Switching (MPLS) Label Switching
              Router (LSR) Management Information Base (MIB)", RFC 3813,
              June 2004, <http://www.rfc-editor.org/info/rfc3813>.

   [RFC3815]  Cucchiara, J., Sjostrand, H., and J. Luciani, "Definitions
              of Managed Objects for the Multiprotocol Label Switching
              (MPLS), Label Distribution Protocol (LDP)", RFC 3815, June
              2004, <http://www.rfc-editor.org/info/rfc3815>.

   [RFC4090]  Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
              Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May
              2005, <http://www.rfc-editor.org/info/rfc4090>.




George & Pignataro            Informational                    [Page 21]

RFC 7439                     IPv6-Only MPLS                 January 2015


   [RFC4220]  Dubuc, M., Nadeau, T., and J. Lang, "Traffic Engineering
              Link Management Information Base", RFC 4220, November
              2005, <http://www.rfc-editor.org/info/rfc4220>.

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

   [RFC4447]  Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
              Heron, "Pseudowire Setup and Maintenance Using the Label
              Distribution Protocol (LDP)", RFC 4447, April 2006,
              <http://www.rfc-editor.org/info/rfc4447>.

   [RFC4558]  Ali, Z., Rahman, R., Prairie, D., and D. Papadimitriou,
              "Node-ID Based Resource Reservation Protocol (RSVP) Hello:
              A Clarification Statement", RFC 4558, June 2006,
              <http://www.rfc-editor.org/info/rfc4558>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, August 2006,
              <http://www.rfc-editor.org/info/rfc4655>.

   [RFC4664]  Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
              Private Networks (L2VPNs)", RFC 4664, September 2006,
              <http://www.rfc-editor.org/info/rfc4664>.

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

   [RFC4762]  Lasserre, M. and V. Kompella, "Virtual Private LAN Service
              (VPLS) Using Label Distribution Protocol (LDP) Signaling",
              RFC 4762, January 2007,
              <http://www.rfc-editor.org/info/rfc4762>.

   [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, February 2007,
              <http://www.rfc-editor.org/info/rfc4798>.

   [RFC4802]  Nadeau, T. and A. Farrel, "Generalized Multiprotocol Label
              Switching (GMPLS) Traffic Engineering Management
              Information Base", RFC 4802, February 2007,
              <http://www.rfc-editor.org/info/rfc4802>.






George & Pignataro            Informational                    [Page 22]

RFC 7439                     IPv6-Only MPLS                 January 2015


   [RFC4875]  Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
              "Extensions to Resource Reservation Protocol - Traffic
              Engineering (RSVP-TE) for Point-to-Multipoint TE Label
              Switched Paths (LSPs)", RFC 4875, May 2007,
              <http://www.rfc-editor.org/info/rfc4875>.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              April 2007, <http://www.rfc-editor.org/info/rfc4884>.

   [RFC4950]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "ICMP
              Extensions for Multiprotocol Label Switching", RFC 4950,
              August 2007, <http://www.rfc-editor.org/info/rfc4950>.

   [RFC4990]  Shiomoto, K., Papneja, R., and R. Rabbat, "Use of
              Addresses in Generalized Multiprotocol Label Switching
              (GMPLS) Networks", RFC 4990, September 2007,
              <http://www.rfc-editor.org/info/rfc4990>.

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, October 2007,
              <http://www.rfc-editor.org/info/rfc5082>.

   [RFC5085]  Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
              Connectivity Verification (VCCV): A Control Channel for
              Pseudowires", RFC 5085, December 2007,
              <http://www.rfc-editor.org/info/rfc5085>.

   [RFC5088]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "OSPF Protocol Extensions for Path Computation Element
              (PCE) Discovery", RFC 5088, January 2008,
              <http://www.rfc-editor.org/info/rfc5088>.

   [RFC5089]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "IS-IS Protocol Extensions for Path Computation Element
              (PCE) Discovery", RFC 5089, January 2008,
              <http://www.rfc-editor.org/info/rfc5089>.

   [RFC5286]  Atlas, A. and A. Zinin, "Basic Specification for IP Fast
              Reroute: Loop-Free Alternates", RFC 5286, September 2008,
              <http://www.rfc-editor.org/info/rfc5286>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, October 2008,
              <http://www.rfc-editor.org/info/rfc5305>.





George & Pignataro            Informational                    [Page 23]

RFC 7439                     IPv6-Only MPLS                 January 2015


   [RFC5329]  Ishiguro, K., Manral, V., Davey, A., and A. Lindem,
              "Traffic Engineering Extensions to OSPF Version 3", RFC
              5329, September 2008,
              <http://www.rfc-editor.org/info/rfc5329>.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440, March
              2009, <http://www.rfc-editor.org/info/rfc5440>.

   [RFC5512]  Mohapatra, P. and E. Rosen, "The BGP Encapsulation
              Subsequent Address Family Identifier (SAFI) and the BGP
              Tunnel Encapsulation Attribute", RFC 5512, April 2009,
              <http://www.rfc-editor.org/info/rfc5512>.

   [RFC5520]  Bradford, R., Vasseur, JP., and A. Farrel, "Preserving
              Topology Confidentiality in Inter-Domain Path Computation
              Using a Path-Key-Based Mechanism", RFC 5520, April 2009,
              <http://www.rfc-editor.org/info/rfc5520>.

   [RFC5521]  Oki, E., Takeda, T., and A. Farrel, "Extensions to the
              Path Computation Element Communication Protocol (PCEP) for
              Route Exclusions", RFC 5521, April 2009,
              <http://www.rfc-editor.org/info/rfc5521>.

   [RFC5640]  Filsfils, C., Mohapatra, P., and C. Pignataro, "Load-
              Balancing for Mesh Softwires", RFC 5640, August 2009,
              <http://www.rfc-editor.org/info/rfc5640>.

   [RFC5837]  Atlas, A., Bonica, R., Pignataro, C., Shen, N., and JR.
              Rivers, "Extending ICMP for Interface and Next-Hop
              Identification", RFC 5837, April 2010,
              <http://www.rfc-editor.org/info/rfc5837>.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, June 2010,
              <http://www.rfc-editor.org/info/rfc5884>.

   [RFC5885]  Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
              Detection (BFD) for the Pseudowire Virtual Circuit
              Connectivity Verification (VCCV)", RFC 5885, June 2010,
              <http://www.rfc-editor.org/info/rfc5885>.

   [RFC5886]  Vasseur, JP., Le Roux, JL., and Y. Ikejiri, "A Set of
              Monitoring Tools for Path Computation Element (PCE)-Based
              Architecture", RFC 5886, June 2010,
              <http://www.rfc-editor.org/info/rfc5886>.




George & Pignataro            Informational                    [Page 24]

RFC 7439                     IPv6-Only MPLS                 January 2015


   [RFC5921]  Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
              Berger, "A Framework for MPLS in Transport Networks",
              RFC 5921, July 2010,
              <http://www.rfc-editor.org/info/rfc5921>.

   [RFC6006]  Zhao, Q., King, D., Verhaeghe, F., Takeda, T., Ali, Z.,
              and J. Meuric, "Extensions to the Path Computation Element
              Communication Protocol (PCEP) for Point-to-Multipoint
              Traffic Engineering Label Switched Paths", RFC 6006,
              September 2010, <http://www.rfc-editor.org/info/rfc6006>.

   [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
              Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011,
              <http://www.rfc-editor.org/info/rfc6073>.

   [RFC6119]  Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
              Engineering in IS-IS", RFC 6119, February 2011,
              <http://www.rfc-editor.org/info/rfc6119>.

   [RFC6371]  Busi, I. and D. Allan, "Operations, Administration, and
              Maintenance Framework for MPLS-Based Transport Networks",
              RFC 6371, September 2011,
              <http://www.rfc-editor.org/info/rfc6371>.

   [RFC6388]  Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
              "Label Distribution Protocol Extensions for Point-to-
              Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, November 2011,
              <http://www.rfc-editor.org/info/rfc6388>.

   [RFC6445]  Nadeau, T., Koushik, A., and R. Cetin, "Multiprotocol
              Label Switching (MPLS) Traffic Engineering Management
              Information Base for Fast Reroute", RFC 6445, November
              2011, <http://www.rfc-editor.org/info/rfc6445>.

   [RFC6513]  Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP
              VPNs", RFC 6513, February 2012,
              <http://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, February 2012,
              <http://rfc-editor.org/info/rfc6514>.

   [RFC6540]  George, W., Donley, C., Liljenstolpe, C., and L. Howard,
              "IPv6 Support Required for All IP-Capable Nodes", BCP 177,
              RFC 6540, April 2012,
              <http://www.rfc-editor.org/info/rfc6540>.



George & Pignataro            Informational                    [Page 25]

RFC 7439                     IPv6-Only MPLS                 January 2015


   [RFC6624]  Kompella, K., Kothari, B., and R. Cherukuri, "Layer 2
              Virtual Private Networks Using BGP for Auto-Discovery and
              Signaling", RFC 6624, May 2012,
              <http://www.rfc-editor.org/info/rfc6624>.

   [RFC6720]  Pignataro, C. and R. Asati, "The Generalized TTL Security
              Mechanism (GTSM) for the Label Distribution Protocol
              (LDP)", RFC 6720, August 2012,
              <http://www.rfc-editor.org/info/rfc6720>.

   [RFC6829]  Chen, M., Pan, P., Pignataro, C., and R. Asati, "Label
              Switched Path (LSP) Ping for Pseudowire Forwarding
              Equivalence Classes (FECs) Advertised over IPv6", RFC
              6829, January 2013,
              <http://www.rfc-editor.org/info/rfc6829>.

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

Acknowledgements

   The authors wish to thank Alvaro Retana, Andrew Yourtchenko, Loa
   Andersson, David Allan, Mach Chen, Mustapha Aissaoui, and Mark Tinka
   for their detailed reviews, as well as Brian Haberman, Joel Jaeggli,
   Adrian Farrel, Nobo Akiya, Francis Dupont, and Tobias Gondrom for
   their comments.

Contributors

   The following people have contributed text to this document:

      Rajiv Asati
      Cisco Systems
      7025 Kit Creek Road
      Research Triangle Park, NC 27709
      United States

      EMail: rajiva@cisco.com











George & Pignataro            Informational                    [Page 26]

RFC 7439                     IPv6-Only MPLS                 January 2015


      Kamran Raza
      Cisco Systems
      2000 Innovation Drive
      Ottawa, ON K2K-3E8
      Canada

      EMail: skraza@cisco.com


      Ronald Bonica
      Juniper Networks
      2251 Corporate Park Drive
      Herndon, VA 20171
      United States

      EMail: rbonica@juniper.net


      Rajiv Papneja
      Huawei Technologies
      2330 Central Expressway
      Santa Clara, CA 95050
      United States

      EMail: rajiv.papneja@huawei.com


      Dhruv Dhody
      Huawei Technologies
      Leela Palace
      Bangalore, Karnataka 560008
      India

      EMail: dhruv.ietf@gmail.com


      Vishwas Manral
      Ionos Networks
      Sunnyvale, CA 94089
      United States

      EMail: vishwas@ionosnetworks.com









George & Pignataro            Informational                    [Page 27]

RFC 7439                     IPv6-Only MPLS                 January 2015


      Nagendra Kumar
      Cisco Systems, Inc.
      7200 Kit Creek Road
      Research Triangle Park, NC 27709
      United States

      EMail: naikumar@cisco.com

Authors' Addresses

   Wesley George (editor)
   Time Warner Cable
   13820 Sunrise Valley Drive
   Herndon, VA  20111
   United States

   Phone: +1-703-561-2540
   EMail: wesley.george@twcable.com


   Carlos Pignataro (editor)
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   United States

   Phone: +1-919-392-7428
   EMail: cpignata@cisco.com























George & Pignataro            Informational                    [Page 28]

