Updates to LDP for IPv6
draft-ietf-mpls-ldp-ipv6-13

MPLS Working Group                                          Rajiv Asati
Internet Draft                                                    Cisco
Updates: 5036 (if approved)
Intended status: Standards Track                         Vishwas Manral
Expires: January 2015                             Hewlett-Packard, Inc.

                                                          Rajiv Papneja
                                                                 Huawei

                                                       Carlos Pignataro
                                                                  Cisco

                                                           July 3, 2014

                          Updates to LDP for IPv6
                        draft-ietf-mpls-ldp-ipv6-13

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 3, 2015.

Copyright Notice

   Copyright (c) 2014 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

Asati, et. al          Expires January 3, 2015                 [Page 1]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008. The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Abstract

   The Label Distribution Protocol (LDP) specification defines
   procedures to exchange label bindings over either IPv4, or IPv6 or
   both networks. This document corrects and clarifies the LDP behavior
   when IPv6 network is used (with or without IPv4). This document
   updates RFC 5036.

Table of Contents

   1. Introduction...................................................3
      1.1. Topology Scenarios for Dual-Stack Environment.............4
      1.2. Single-hop vs. Multi-hop LDP Peering......................5
   2. Specification Language.........................................6
   3. LSP Mapping....................................................6
   4. LDP Identifiers................................................7
   5. Neighbor Discovery.............................................7
      5.1. Basic Discovery Mechanism.................................8
         5.1.1. Maintaining Hello Adjacencies........................9
      5.2. Extended Discovery Mechanism..............................9
   6. LDP Session Establishment and Maintenance......................9
      6.1. Transport connection establishment........................9
         6.1.1. Determining Transport connection Roles..............11
      6.2. LDP Sessions Maintenance.................................13
   7. Address Distribution..........................................14
   8. Label Distribution............................................14

Asati, et. al          Expires January 3, 2015                 [Page 2]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   9. LDP Identifiers and Duplicate Next Hop Addresses..............15
   10. LDP TTL Security.............................................16
   11. IANA Considerations..........................................16
   12. Security Considerations......................................16
   13. Acknowledgments..............................................17
   14. Additional Contributors......................................17
   15. References...................................................18
      15.1. Normative References....................................18
      15.2. Informative References..................................18
   Appendix A.......................................................20
      A.1. LDPv6 and LDPv4 Interoperability Safety Net..............20
      A.2. Why 32-bit value even for IPv6 LDP Router ID.............20
      A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........20
   Author's Addresses...............................................22

1. Introduction

   The LDP [RFC5036] specification defines procedures and messages for
   exchanging FEC-label bindings over either IPv4 or IPv6 or both (e.g.
   dual-stack) networks.

   However, RFC5036 specification has the following deficiency (or
   lacks details) in regards to IPv6 usage (with or without IPv4):

   1) LSP Mapping: No rule for mapping a particular packet to a
      particular LSP that has an Address Prefix FEC element containing
      IPv6 address of the egress router

   2) LDP Identifier: No details specific to IPv6 usage

   3) LDP Discovery: No details for using a particular IPv6 destination
      (multicast) address or the source address (with or without IPv4
      co-existence)

   4) LDP Session establishment: No rule for handling both IPv4 and
      IPv6 transport address optional objects in a Hello message, and
      subsequently two IPv4 and IPv6 transport connections

   5) LDP Address Distribution: No rule for advertising IPv4 or/and
      IPv6 FEC-Address bindings over an LDP session

Asati, et. al          Expires January 3, 2015                 [Page 3]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   6) LDP Label Distribution: No rule for advertising IPv4 or/and IPv6
      FEC-label bindings over an LDP session, and for handling the co-
      existence of IPv4 and IPv6 FEC Elements in the same FEC TLV

   7) Next Hop Address Resolution: No rule for accommodating the usage
      of duplicate link-local IPv6 addresses

   8) LDP TTL Security: No rule for built-in Generalized TTL Security
      Mechanism (GTSM) in LDP with IPv6 (this is a deficiency in
      RFC6720)

   This document addresses the above deficiencies by specifying the
   desired behavior/rules/details for using LDP in IPv6 enabled
   networks (IPv6-only or Dual-stack networks).

   Note that this document updates RFC5036 and RFC6720.

1.1. Topology Scenarios for Dual-Stack Environment

   Two LSRs may involve basic and/or extended LDP discovery in IPv6
   and/or IPv4 address-families in various topology scenarios.

   This document addresses the following 3 topology scenarios in which
   the LSRs may be connected via one or more dual-stack interfaces
   (figure 1), or one or more single-stack interfaces (figure 2 and
   figure 3):

                 R1------------------R2
                       IPv4+IPv6

            Figure 1 LSRs connected via a Dual-stack Interface

                       IPv4
                 R1=================R2
                       IPv6

          Figure 2 LSRs connected via two single-stack Interfaces

Asati, et. al          Expires January 3, 2015                 [Page 4]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

                 R1------------------R2---------------R3
                       IPv4                 IPv6

           Figure 3 LSRs connected via a single-stack Interface

   Note that the topology scenario illustrated in figure 1 also covers
   the case of a single-stack interface (IPv4, say) being converted to
   a dual-stacked interface by enabling IPv6 routing as well as IPv6
   LDP, even though the IPv4 LDP session may already be established
   between the LSRs.

   Note that the topology scenario illustrated in figure 2 also covers
   the case of two routers getting connected via an additional single-
   stack interface (IPv6 routing and IPv6 LDP), even though the IPv4
   LDP session may already be established between the LSRs over the
   existing interface(s).

   This document also addresses the scenario in which the LSRs do
   extended discovery in IPv6 and/or IPv4 address-families:

                          IPv4
                 R1-------------------R2
                          IPv6

          Figure 4 LSRs involving IPv4 and IPv6 address-families

1.2. Single-hop vs. Multi-hop LDP Peering

   LDP TTL Security mechanism specified by this document applies only
   to single-hop LDP peering sessions, but not to multi-hop LDP peering
   sessions, in line with Section 5.5 of [RFC5082] that describes
   Generalized TTL Security Mechanism (GTSM).

   As a consequence, any LDP feature that relies on multi-hop LDP
   peering session would not work with GTSM and will warrant
   (statically or dynamically) disabling GTSM. Please see section 10.

Asati, et. al          Expires January 3, 2015                 [Page 5]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

2. Specification Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Abbreviations:

   LDP      - Label Distribution Protocol

   LDPoIPv4 - LDP over IPv4 transport session

   LDPoIPv6 - LDP over IPv6 transport session

   FEC      - Forwarding Equivalence Class

   TLV      - Type Length Value

   LSR      - Label Switching Router

   LSP      - Label Switched Path

   LSPv4    - IPv4-signaled Label Switched Path [RFC4798]

   LSPv6    - IPv6-signaled Label Switched Path [RFC4798]

   AFI      - Address Family Identifier

   LDP Id   - LDP Identifier

3. LSP Mapping

   Section 2.1 of [RFC5036] specifies the procedure for mapping a
   particular packet to a particular LSP using three rules. Quoting the
   3rd rule from RFC5036:

     "If it is known that a packet must traverse a particular egress
     router, and there is an LSP that has an Address Prefix FEC element
     that is a /32 address of that router, then the packet is mapped to
     that LSP."

Asati, et. al          Expires January 3, 2015                 [Page 6]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   This rule is correct for IPv4, but not for IPv6, since an IPv6
   router may even have a /64 or /96 or /128 (or whatever prefix
   length) address. Hence, it is reasonable to say IPv4 or IPv6 address
   instead of /32 or /128 addresses as shown below in the updated rule:

     "If it is known that a packet must traverse a particular egress
     router, and there is an LSP that has an Address Prefix FEC element
     that is an IPv4 or IPv6 address of that router, then the packet is
     mapped to that LSP."

4. LDP Identifiers

   In line with section 2.2.2 of [RFC5036], this document specifies the
   usage of 32-bit (unsigned non-zero integer) LSR Id on an IPv6
   enabled LSR (with or without dual-stacking).

   This document also qualifies the first sentence of last paragraph of
   Section 2.5.2 of [RFC5036] to be per address family and therefore
   updates that sentence to the following:

     "For a given address family, an LSR MUST advertise the same
     transport address in all Hellos that advertise the same label
     space."

   This rightly enables the per-platform label space to be shared
   between IPv4 and IPv6.

   In summary, this document mandates the usage of a common LDP
   identifier (same LSR Id aka LDP Router Id as well as a common Label
   space id) for both IPv4 and IPv6 address families on a dual-stack
   LSR.

5. Neighbor Discovery

   If an LSR is enabled with dual-stack LDP (e.g. LDP enabled in both
   IPv6 and IPv4 address families), then the LSR MUST advertise both
   IPv6 and IPv4 LDP Link or targeted Hellos and include the same LDP
   Identifier (assuming per-platform label space usage) in them.

   If an LSR is enabled with single-stack LDP (e.g. LDP enabled in
   either IPv6 or IPv4 address family), then the LSR MUST advertise
   either IPv6 or IPv4 LDP Link or targeted Hellos respectively.

Asati, et. al          Expires January 3, 2015                 [Page 7]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

5.1. Basic Discovery Mechanism

   Section 2.4.1 of [RFC5036] defines the Basic Discovery mechanism for
   directly connected LSRs. Following this mechanism, LSRs periodically
   send LDP Link Hellos destined to "all routers on this subnet" group
   multicast IP address.

   Interesting enough, per the IPv6 addressing architecture [RFC4291],
   IPv6 has three "all routers on this subnet" multicast addresses:

         FF01:0:0:0:0:0:0:2   = Interface-local scope

         FF02:0:0:0:0:0:0:2   = Link-local scope

         FF05:0:0:0:0:0:0:2   = Site-local scope

   [RFC5036] does not specify which particular IPv6 'all routers on
   this subnet' group multicast IP address should be used by LDP Link
   Hellos.

   This document specifies the usage of link-local scope e.g.
   FF02:0:0:0:0:0:0:2 as the destination multicast IP address in IPv6
   LDP Link Hellos. An LDP Hello packet received on any of the other
   destination addresses MUST be dropped. Additionally, the link-local
   IPv6 address MUST be used as the source IP address in IPv6 LDP Link
   Hellos.

   Also, the LDP Link Hello packets MUST have their IPv6 Hop Limit set
   to 255, be checked for the same upon receipt (before any LDP
   specific processing) and be handled as specified in Generalized TTL
   Security Mechanism (GTSM) section 3 of [RFC5082]. The built-in
   inclusion of GTSM automatically protects IPv6 LDP from off-link
   attacks.

   More importantly, if an interface is a dual-stack LDP interface
   (e.g. LDP enabled in both IPv6 and IPv4 address families), then the
   LSR MUST periodically send both IPv6 and IPv4 LDP Link Hellos (using
   the same LDP Identifier per section 4) on that interface and be able
   to receive them. This facilitates discovery of IPv6-only, IPv4-only
   and dual-stack peers on the interface's subnet and ensures
   successful subsequent peering using the appropriate (address family)
   transport on a multi-access or broadcast interface.

   An implementation MUST send IPv6 LDP link Hellos before sending IPv4
   LDP Link Hellos on a dual-stack interface.

Asati, et. al          Expires January 3, 2015                 [Page 8]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

5.1.1. Maintaining Hello Adjacencies

   In case of dual-stack LDP interface (e.g. LDP enabled in both IPv6
   and IPv4 address families), the LSR SHOULD maintain link Hello
   adjacencies for both IPv4 and IPv6 address families. This document,
   however, allows an LSR to maintain Rx-side Link Hello adjacency for
   the address family that has been used for the establishment of the
   LDP session (either IPv4 or IPv6).

5.2. Extended Discovery Mechanism

   The extended discovery mechanism (defined in section 2.4.2 of
   [RFC5036]), in which the targeted LDP Hellos are sent to a pre-
   configured (unicast) destination IPv6 address, requires only one
   IPv6 specific consideration: the link-local IPv6 addresses MUST NOT
   be used as the targeted LDP hello packet's source or destination
   addresses.

6. LDP Session Establishment and Maintenance

   Section 2.5.1 of [RFC5036] defines a two-step process for LDP
   session establishment, once the peer discovery has completed (LDP
   Hellos have been exchanged):

     1. Transport connection establishment
     2. Session initialization

   The forthcoming sub-section 6.1 discusses the LDP consideration for
   IPv6 and/or dual-stacking in the context of session establishment,
   whereas sub-section 6.2 discusses the LDP consideration for IPv6
   and/or dual-stacking in the context of session maintenance.

6.1. Transport connection establishment

   Section 2.5.2 of [RFC5036] specifies the use of an optional
   transport address object (TLV) in LDP Hello message to convey the
   transport (IP) address, however, it does not specify the behavior of
   LDP if both IPv4 and IPv6 transport address objects (TLV) are sent
   in a Hello message or separate Hello messages. More importantly, it

Asati, et. al          Expires January 3, 2015                 [Page 9]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   does not specify whether both IPv4 and IPv6 transport connections
   should be allowed, if there were both IPv4 and IPv6 Hello
   adjacencies.

   This document specifies that:

     1. An LSR MUST NOT send a Hello message containing both IPv4 and
        IPv6 transport address optional objects. In other words, there
        MUST be at most one optional Transport Address object in a
        Hello message. An LSR MUST include only the transport address
        whose address family is the same as that of the IP packet
        carrying Hello message.

     2. An LSR SHOULD accept the Hello message that contains both IPv4
        and IPv6 transport address optional objects, but MUST use only
        the transport address whose address family is the same as that
        of the IP packet carrying the Hello message. An LSR SHOULD
        accept only the first transport object for a given Address
        family in the received Hello message, and ignore the rest, if
        the LSR receives more than one transport object.

     3. An LSR MUST send separate Hello messages (each containing
        either IPv4 or IPv6 transport address optional object) for each
        IP address family, if LDP was enabled for both IP address
        families.

     4. An LSR MUST use a global unicast IPv6 address in IPv6 transport
        address optional object of outgoing targeted Hellos, and check
        for the same in incoming targeted hellos (i.e. MUST discard the
        hello, if it failed the check).

     5. An LSR MUST prefer using a global unicast IPv6 address in IPv6
        transport address optional object of outgoing Link Hellos, if
        it had to choose between global unicast IPv6 address and
        unique-local or link-local IPv6 address.

     6. An LSR SHOULD NOT create (or honor the request for creating) a
        TCP connection for a new LDP session with a remote LSR, if they
        already have an LDP session (for the same LDP Identifier)
        established over whatever IP version transport.

        This means that only one transport connection is established
        regardless of IPv6 or/and IPv4 Hello adjacencies presence
        between two LSRs.

     7. An LSR SHOULD prefer the LDP/TCP connection over IPv6 for a new
        LDP session with a remote LSR, if it is able to determine the

Asati, et. al          Expires January 3, 2015                [Page 10]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

        IPv6 presence (e.g. IPv6 Hello adjacency), by following the
        'transport connection role' determination logic in section
        6.1.1.

6.1.1. Determining Transport connection Roles

   Section 2.5.2 of [RFC5036] specifies the rules for determining
   active/passive roles in setting up TCP connection. These rules are
   clear for a single-stack (IPv4 or IPv6) LDP, but not for a dual-
   stack (IPv4 and IPv6) LDP, in which an LSR may assume different
   roles for different address families, causing LDP session to not get
   established.

   To ensure deterministic transport connection (active/passive) role
   for dual-stack LDP peering, this document specifies that the LSR
   convey its transport connection preference in every LDP Hello
   message. A new optional parameter, encoded as a TLV, (section 3.5.2
   of RFC5036) is defined as follows (for Hello Message):

      0                  1                   2                  3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7  9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1|0|   IPv4orIPv6 Preference |        Length                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |TR |  Reserved               |     MBZ                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 5 IPv4 or IPv6 Transport Preference TLV

   Where:

      U and F bits: 1 and 0 (as specified by RFC5036)

      IPv4orIPv6 Preference: TLV code point for IPv4 or IPv6 Preference
      (to be assigned by IANA).

      TR,   Transport Preference

            00: IPv4

            01: IPv6 (default value)

Asati, et. al          Expires January 3, 2015                [Page 11]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

      Reserved

            This field is reserved.  It MUST be set to zero on
            transmission and ignored on receipt.

   A dual-stack LDP enabled LSR (capable of supporting both IPv4 and
   IPv6 transports for LDP) MUST include "IPv4orIPv6 Transport
   Preference" optional parameter in all of its LDP Hellos, and MUST
   set the "TR" field to announce its preference for either IPv4 or
   IPv6 transport connection. The default preference is IPv6.

   Upon receiving the hello message with this TLV, a dual-stack capable
   receiving LSR MUST do the following:

     1. If it understands the TLV, and if neighbor's preference does
        not match with the local preference, then it discards the hello
        (and no adjacency is formed) and logs an error.

     2. If it understands the TLV, and if neighbor's preference matches
        with the local preference, then:

          a) If TR=0 (IPv4), then determine the active/passive roles
             for TCP connection using IPv4 transport address as defined
             in section 2.5.2 of RFC 5036.

          b) If TR=1 (IPv6), then determine the active/passive roles
             for TCP connection by comparing the LSR Id part of the LDP
             Identifiers of LSRs.

             The LSR with higher LSR Id MUST assume the active role and
             other LSR MUST assume the passive role for the IPv6 TCP
             connection.

     3. If it does not understand the TLV, then it MUST silently
        discard this TLV and process the rest of the Hello message.

   If an LSR receives the hello message without the "IPv4orIPv6
   Transport Preference" TLV, then it MUST proceed with session
   establishment using single-stack rules, as per section 2.5.2 of RFC
   5036.

   An LSR MUST convey the same transport connection preference ("TR"
   field) in all (link and targeted) Hellos that advertise the same
   label space to the same peer and/or on same interface.  This ensures
   that two LSRs linked by multiple Hello adjacencies using the same

Asati, et. al          Expires January 3, 2015                [Page 12]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   label spaces play the same connection establishment role for each
   adjacency.

   An implementation may provide an option to favor one AFI (IPv4, say)
   over another AFI (IPv6, say) for the TCP transport connection, so as
   to use the favored IP version for the LDP session, and force
   deterministic active/passive roles.

   Note - An alternative to Capability TLV could be a new Flag value in
   LDP Hello message, however, it will get used even in a single-stack
   IPv6 scenarios and linger on forever, even though dual-stack will
   not. Hence, this alternative is discarded.

6.2. LDP Sessions Maintenance

   This document specifies that two LSRs maintain a single LDP session
   regardless of number of Link or Targeted Hello adjacencies between
   them, as described in section 6.1. This is independent of whether:

   - they are connected via a dual-stack LDP enabled interface(s) or
     via two (or more) single-stack LDP enabled interfaces;
   - a single-stack LDP enabled interface is converted to a dual-stack
     LDP enabled interface (e.g. figure 1) on either LSR;
   - an additional single-stack or dual-stack LDP enabled interface is
     added or removed between two LSRs (e.g. figure 2).

   The procedures defined in section 6.1 SHOULD result in preferring
   LDPoIPv6 session only after the loss of an existing LDP session
   (because of link failure, node failure, reboot etc.).

   If the last hello adjacency for a given address family goes down
   (e.g. due to dual-stack LDP enabled interfaces being converted into
   a single-stack LDP enabled interfaces on one LSR etc.), and that
   address family is the same as the one used in the transport
   connection, then the transport connection (LDP session) SHOULD be
   reset. Otherwise, the LDP session SHOULD stay intact.

   If the LDP session is torn down for whatever reason (LDP disabled
   for the corresponding transport, hello adjacency expiry etc.), then
   the LSRs SHOULD initiate establishing a new LDP session as per the
   procedures described in section 6.1 of this document.

Asati, et. al          Expires January 3, 2015                [Page 13]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

7. Address Distribution

   If an LSR is enabled with dual-stack LDP (i.e. LDP in both IPv4 and
   IPv6 address families) for any (discovered or targeted) peer, then
   it MUST advertise (via ADDRESS message) its local IPv4 and IPv6
   addresses to that peer by default, independent of the transport
   connection (address family) used for that peering.

   If an LSR, compliant with this specification, is enabled with
   single-stack LDP (i.e. LDP in either IPv6 or IPv4 address family)
   for any (discovered or targeted) peer, then it MUST advertise (via
   ADDRESS message) its local IP addresses as per the enabled address
   family by default, and SHOULD accept a received Address message
   containing both IPv4 and IPv6 addresses.

8. Label Distribution

   An LSR MUST NOT allocate and MUST NOT advertise FEC-Label bindings
   for link-local or IPv4-mapped IPv6 addresses (defined in section
   2.5.5.2 of [RFC4291]), and ignore such bindings, if ever received.
   Please see Appendix A.3.

   Additionally, to ensure backward compatibility (and interoperability
   with IPv4-only LDP implementations) in light of section 3.4.1.1 of
   RFC5036, as rationalized in the Appendix section A.1 later, this
   document specifies that -

     1. An LSR MUST NOT send a label mapping message with a FEC TLV
        containing two or more Prefix FEC Elements of different address
        families. This means that a FEC TLV in the label mapping
        message must contain all the Prefix FEC Elements belonging to
        IPv6 address family or IPv4 address family, but not both.

   If an LSR is enabled with dual-stack LDP (i.e. LDP in both IPv4 and
   IPv6 address families) for any peer, then it MUST advertise the FEC-
   Label bindings for both IPv4 and IPv6 address families to that peer.
   However, an LSR MAY constrain the advertisement of FEC-label
   bindings for a particular address family by negotiating the IP
   Capability for a given address family, as specified in [IPPWCap]
   document. This allows an LSR pair to neither advertise nor receive
   the undesired FEC-label bindings on a per address family basis.

   If an LSR is configured to move an interface or peer from single-
   stack (IPv6 or IPv4 address family) to dual-stack LDP (IPv6 and IPv4

Asati, et. al          Expires January 3, 2015                [Page 14]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   address families), then an LSR SHOULD use Typed Wildcard FEC
   procedures [RFC5918] to request the FEC-label bindings for the
   enabled address family. This helps to relearn the FEC-label bindings
   that may have been discarded before without resetting the peering.

9. LDP Identifiers and Duplicate Next Hop Addresses

   RFC5036 section 2.7 specifies the logic for mapping the IP routing
   next-hop (of a given FEC) to an LDP peer so as to find the correct
   label entry for that FEC. The logic involves using the IP routing
   next-hop address as an index into the (peer Address) database (which
   is populated by the Address message containing mapping between each
   peer's local addresses and its LDP Identifier) to determine the LDP
   peer.

   However, this logic is insufficient to deal with duplicate IPv6
   (link-local) next-hop addresses used by two or more peers. The
   reason is that all interior IPv6 routing protocols (can) use link-
   local IPv6 addresses as the IP routing next-hops, and 'IPv6
   Addressing Architecture [RFC4291]' allows a link-local IPv6 address
   to be used on more than one links.

   Hence, this logic is extended by this specification to use not only
   the IP routing next-hop address, but also the IP routing next-hop
   interface to uniquely determine the LDP peer(s). The next-hop
   address-based LDP peer mapping is to be done through LDP peer
   address database (populated by Address messages received from the
   LDP peers), whereas next-hop interface-based LDP peer mapping is to
   be done through LDP hello adjacency/interface database (populated by
   hello messages from the LDP peers).

   This extension solves the problem of two or more peers using the
   same link-local IPv6 address (in other words, duplicate peer
   addresses) as the IP routing next-hops.

   Lastly, for better scale and optimization, an LSR may advertise only
   the link-local IPv6 addresses in the Address message, assuming that
   the peer uses only the link-local IPv6 addresses as static and/or
   dynamic IP routing next-hops.

Asati, et. al          Expires January 3, 2015                [Page 15]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

10. LDP TTL Security

   This document recommends enabling Generalized TTL Security Mechanism
   (GTSM) for LDP, as specified in [RFC6720], for the LDP/TCP transport
   connection over IPv6 (i.e. LDPoIPv6). The GTSM inclusion is intended
   to automatically protect IPv6 LDP peering session from off-link
   attacks.

   [RFC6720] allows for the implementation to statically
   (configuration) and/or dynamically override the default behavior
   (enable/disable GTSM) on a per-peer basis. Suffice to say that such
   an option could be set on either LSR (since GTSM negotiation would
   ultimately disable GTSM between LSR and its peer(s)).

   LDP Link Hello packets MUST have their IPv6 Hop Limit set to 255,
   and be checked for the same upon receipt before any further
   processing, as per section 3 of [RFC5082].

11. IANA Considerations

   This document defines a new optional parameter for the LDP Hello
   Message. The type code needs to be assigned by IANA.

12. Security Considerations

   The extensions defined in this document only clarify the behavior of
   LDP, they do not define any new protocol procedures. Hence, this
   document does not add any new security issues to LDP.

   While the security issues relevant for the [RFC5036] are relevant
   for this document as well, this document reduces the chances of off-
   link attacks when using IPv6 transport connection by including the
   use of GTSM procedures [RFC5082]. Please see section 9 for LDP TTL
   Security details.

   Moreover, this document allows the use of IPsec [RFC4301] for IPv6
   protection, hence, LDP can benefit from the additional security as
   specified in [RFC4835] as well as [RFC5920].

Asati, et. al          Expires January 3, 2015                [Page 16]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

13. Acknowledgments

   We acknowledge the authors of [RFC5036], since some text in this
   document is borrowed from [RFC5036].

   Thanks to Bob Thomas for providing critical feedback to improve this
   document early on.

   Many thanks to Eric Rosen, Lizhong Jin, Bin Mo, Mach Chen, Shane
   Amante, Pranjal Dutta, Mustapha Aissaoui, Matthew Bocci, Mark Tinka,
   Tom Petch, Kishore Tiruveedhula, Manoj Dutta, Vividh Siddha, Qin Wu,
   Simon Perreault, Brian E Carpenter, and Loa Andersson for thoroughly
   reviewing this document, and providing insightful comments and
   multiple improvements.

   This document was prepared using 2-Word-v2.0.template.dot.

14. Additional Contributors

   The following individuals contributed to this document:

   Kamran Raza
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, ON K2K-3E8, Canada
   Email: skraza@cisco.com

   Nagendra Kumar
   Cisco Systems, Inc.
   SEZ Unit, Cessna Business Park,
   Bangalore, KT, India
   Email: naikumar@cisco.com

   Andre Pelletier
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, ON K2K-3E8, Canada
   Email: apelleti@cisco.com

Asati, et. al          Expires January 3, 2015                [Page 17]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

15. References

15.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4291] Hinden, R. and S. Deering, "Internet Protocol Version 6
             (IPv6) Addressing Architecture", RFC 4291, February 2006.

   [RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP
             Specification", RFC 5036, October 2007.

   [RFC5082] Pignataro, C., Gill, V., Heasley, J., Meyer, D., and
             Savola, P., "The Generalized TTL Security Mechanism
             (GTSM)", RFC 5082, October 2007.

   [RFC5918] Asati, R., Minei, I., and Thomas, B., "Label Distribution
             Protocol (LDP) 'Typed Wildcard Forward Equivalence Class
             (FEC)", RFC 5918, October 2010.

15.2. Informative References

   [RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet
             Protocol", RFC 4301, December 2005.

   [RFC4835] Manral, V., "Cryptographic Algorithm Implementation
             Requirements for Encapsulating Security Payload (ESP) and
             Authentication Header (AH)", RFC 4835, April 2007.

   [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS
             Networks", RFC 5920, July 2010.

   [RFC4798] De Clercq, et al., "Connecting IPv6 Islands over IPv4 MPLS
             Using IPv6 Provider Edge Routers (6PE)", RFC 4798,
             February 2007.

   [IPPWCap] Raza, K., "LDP IP and PW Capability", draft-ietf-mpls-ldp-
             ip-pw-capability, June 2011.

   [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
             for IPv6", RFC 5340, July 2008.

Asati, et. al          Expires January 3, 2015                [Page 18]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   [RFC6286] E. Chen, and J. Yuan, "Autonomous-System-Wide Unique BGP
             Identifier for BGP-4", RFC 6286, June 2011.

   [RFC6720] R. Asati, and C. Pignataro, "The Generalized TTL Security
             Mechanism (GTSM) for the Label Distribution Protocol
             (LDP)", RFC 6720, August 2012.

   [RFC4038] M-K. Shin, Y-G. Hong, J. Hagino, P. Savola, and E. M.
             Castro, "Application Aspects of IPv6 Transition", RFC
             4038, March 2005.

Asati, et. al          Expires January 3, 2015                [Page 19]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

Appendix A.

A.1. LDPv6 and LDPv4 Interoperability Safety Net

   It is naive to assume that RFC5036 compliant implementations have
   supported IPv6 address family (IPv6 FEC processing, in particular)
   in label advertisement all along. And if that assumption turned out
   to be not true, then section 3.4.1.1 of RFC5036 would cause LSRs to
   abort processing the entire label mapping message and generate an
   error.

   This would result in LDPv6 to be somewhat undeployable in existing
   production networks.

   The change proposed in section 7 of this document provides a good
   safety net and makes LDPv6 incrementally deployable without making
   any such assumption on the routers' support for IPv6 FEC processing
   in current production networks.

A.2. Why 32-bit value even for IPv6 LDP Router ID

   The first four octets of the LDP identifier, the 32-bit LSR Id (e.g.
   (i.e. LDP Router Id), identify the LSR and is a globally unique
   value within the MPLS network. This is regardless of the address
   family used for the LDP session.

   Please note that 32-bit LSR Id value would not map to any IPv4-
   address in an IPv6 only LSR (i.e., single stack), nor would there be
   an expectation of it being IP routable, nor DNS-resolvable. In IPv4
   deployments, the LSR Id is typically derived from an IPv4 address,
   generally assigned to a loopback interface. In IPv6 only
   deployments, this 32-bit LSR Id must be derived by some other means
   that guarantees global uniqueness within the MPLS network, similar
   to that of BGP Identifier [RFC6286] and OSPF router ID [RFC5340].

   This document reserves 0.0.0.0 as the LSR Id, and prohibits its
   usage with IPv6, in line with OSPF router Id in OSPF version 3
   [RFC5340].

A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP

Asati, et. al          Expires January 3, 2015                [Page 20]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

   Per discussion with 6MAN and V6OPS working groups, the overwhelming
   consensus was to not promote IPv4-mapped IPv6 addresses appear in
   the routing table, as well as in LDP (address and label) databases.

   Also, [RFC4038] section 4.2 suggests that IPv4-mapped IPv6 addressed
   packets should never appear on the wire.

Asati, et. al          Expires January 3, 2015                [Page 21]
Internet-Draft         draft-ietf-mpls-ldp-ipv6            July 3, 2014

Author's Addresses

   Vishwas Manral
   Hewlet-Packard, Inc.
   19111 Pruneridge Ave., Cupertino, CA, 95014
   Phone: 408-447-1497
   Email: vishwas.manral@hp.com

   Rajiv Papneja
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, CA  95050
   Phone: +1 571 926 8593
   EMail: rajiv.papneja@huawei.com

   Rajiv Asati
   Cisco Systems, Inc.
   7025 Kit Creek Road
   Research Triangle Park, NC 27709-4987
   Email: rajiva@cisco.com

   Carlos Pignataro
   Cisco Systems, Inc.
   7200 Kit Creek Road
   Research Triangle Park, NC 27709-4987
   Email: cpignata@cisco.com

Asati, et. al          Expires January 3, 2015                [Page 22]