MPLS Working Group                                          Rajiv Asati
Internet Draft                                                    Cisco                                         Carlos Pignataro
Updates: 5036 5036, 6720 (if approved)                           Kamran Raza
Intended status: Standards Track                         Vishwas Manral                                  Cisco
Expires: January April 2015
                                                         Vishwas Manral
                                                   Hewlett-Packard, Inc. Inc

                                                          Rajiv Papneja
                                                                 Huawei

                                                       Carlos Pignataro
                                                                  Cisco

                                                           July 3,

                                                        October 2, 2014

                          Updates to LDP for IPv6
                        draft-ietf-mpls-ldp-ipv6-13
                        draft-ietf-mpls-ldp-ipv6-14

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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. 5036 and RFC 6720.

Table of Contents

   1. Introduction...................................................3
      1.1. Topology Scenarios for Dual-Stack Dual-stack Environment.............4
      1.2. Single-hop vs. Multi-hop LDP Peering......................5
   2. Specification Language.........................................6
   3. LSP Mapping....................................................6 Mapping....................................................7
   4. LDP Identifiers................................................7
   5. Neighbor Discovery.............................................7 Discovery.............................................8
      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 establishment.......................10
         6.1.1. Determining Transport connection Roles..............11
      6.2. LDP Sessions Maintenance.................................13 Maintenance.................................14
   7. Address Binding Distribution..........................................14
   8.
      7.1. Address Distribution.....................................15
      7.2. Label Distribution............................................14
   9. Distribution.......................................15

   8. LDP Identifiers and Duplicate Next Hop Addresses..............15
   10. Addresses..............16
   9. LDP TTL Security.............................................16
   11. Security..............................................17
   10. IANA Considerations..........................................16
   12. Considerations..........................................18
   11. Security Considerations......................................16 Considerations......................................18
   12. Acknowledgments..............................................19
   13. Acknowledgments..............................................17
   14. Additional Contributors......................................17
   15. References...................................................18
      15.1. Contributors......................................19
   14. References...................................................20
      14.1. Normative References....................................18
      15.2. References....................................20
      14.2. Informative References..................................18 References..................................20
   Appendix A.......................................................20 A.......................................................22
      A.1. LDPv6 and LDPv4 Interoperability Safety Net..............20 Net..............22
      A.2. Accommodating Non-RFC5036-compliant implementations......22
      A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........23
      A.4. Why 32-bit value even for IPv6 LDP Router ID.............20
      A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........20 ID.............23
   Author's Addresses...............................................22 Addresses...............................................24

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)
   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 Address bindings over an LDP session

   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 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 Dual-stack LDP enabled
   interfaces (figure 1), or one or more single-stack Single-stack LDP enabled
   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 Single-stack Interfaces
                 R1------------------R2---------------R3
                       IPv4                 IPv6

           Figure 3 LSRs connected via a single-stack Single-stack Interface

   Note that the topology scenario illustrated in figure 1 also covers
   the case of a single-stack Single-stack LDP enabled interface (IPv4, say) being
   converted to a dual-stacked Dual-stacked LDP enabled interface by (by enabling IPv6
   routing as well as IPv6
   LDP, LDP), even though the IPv4 LDP LDPoIPv4 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- Single-
   stack LDP enabled interface (IPv6 routing and IPv6 LDP), even though
   the IPv4
   LDP LDPoIPv4 session may already be established between the LSRs
   over the existing interface(s).

   This document also addresses the scenario in which the LSRs do the
   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.

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 connection

   LDPoIPv6 - LDP over IPv6 transport session connection

   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

   Single-stack LDP - LDP supporting just one address family (for
                    discovery, session setup, address/label binding
                    exchange etc.)

   Dual-stack LDP   - LDP supporting two address families (for
                    discovery, session setup, address/label binding
                    exchange etc.)

   Dual-stack LSR    - LSR supporting Dual-stack LDP for a peer

   Single-stack LSR  - LSR supporting Single-stack LDP for a peer

   Note that an LSR can be a Dual-stack and Single-stack LSR at the
   same time for different peers. This document loosely uses the term
   address family to mean IP address family.

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."

   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). 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. families.

5. Neighbor Discovery

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

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

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 Link Hello packet received on any of the
   other destination addresses MUST be dropped. Additionally, the link-local 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 Dual-stack LDP interface
   (e.g. LDP enabled in both IPv6 and IPv4 address families), then the
   LSR MUST periodically send transmit 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 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 transmit IPv6 LDP link Hellos before sending IPv4 LDP
   Link Hellos on a dual-stack interface. Dual-stack interface, particularly during the
   interface coming into service or configuration time.

5.1.1. Maintaining Hello Adjacencies

   In case of dual-stack LDP interface (e.g. Dual-stack LDP enabled in both IPv6
   and IPv4 address families), interface, 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 only for the address family that has been used for the
   establishment of the LDP session (either IPv4 (whether LDPoIPv4 or IPv6). LDPoIPv6
   session).

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 unicast
   IPv6 address, address destination, 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 neighbor discovery has completed (LDP
   (i.e. 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 Dual-stacking in the context of session establishment,
   whereas sub-section 6.2 discusses the LDP consideration for IPv6
   and/or dual-stacking 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
   does not specify whether both IPv4 and IPv6 transport connections
   should be allowed, if there were both IPv4 and IPv6 Hello
   adjacencies. adjacencies were
   present prior to the session establishment.

   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 the 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 address
        family in the received Hello message, and ignore the rest, if
        the LSR receives more than one transport object. object for a given
        address family.

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

     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
        targeted 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 A Dual-stack LSR SHOULD MUST NOT create initiate (or honor accept the request for creating) for)
        a TCP connection for a new LDP session with a remote LSR, if
        they already have an LDP session (for LDPoIPv4 or LDPoIPv6 session (for the same
        LDP Identifier)
        established over whatever IP version transport. established.

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

     7. An A Dual-stack LSR SHOULD MUST prefer the LDP/TCP connection over IPv6 for a new
        LDP establishing LDPoIPv6 session with
        a remote LSR, if it is able to determine the
        IPv6 presence (e.g. IPv6 Hello adjacency), LSR by following the 'transport connection role'
        determination logic in section 6.1.1.

     8.  A Single-stack LSR MUST establish LDPoIPv4 or LDPoIPv6 session
        with a remote LSR as per the enabled address-family.

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) Single-stack LDP, but not for a dual-
   stack (IPv4 and IPv6) Dual-stack 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,
   in case of Dual-stack LDP, this document specifies that the Dual-
   stack LSR convey its transport connection preference in every LDP
   Hello message. A new optional parameter, This preference is encoded as in a new TLV, named Dual-
   stack capability TLV, (section 3.5.2
   of RFC5036) is defined as follows (for Hello Message): defined below:

      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  Dual-stack capability  |        Length                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |TR     |      Reserved       |     MBZ                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 5 IPv4 or IPv6 Transport Preference Dual-stack capability TLV

   Where:

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

      IPv4orIPv6 Preference:

      Dual-stack capability: TLV code point for IPv4 or IPv6 Preference (to be assigned by IANA).

      TR,   Transport Preference

            00: IPv4

            01: IPv6 (default value) Connection Preference.

            This document defines the following 2 values:

            0100: LDPoIPv4 connection

            0110: LDPoIPv6 connection

      Reserved

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

   A dual-stack LDP enabled Dual-stack LSR (capable of supporting both IPv4 and
   IPv6 transports for LDP) MUST include "IPv4orIPv6 Transport
   Preference" optional parameter "Dual-stack capability" TLV in all of
   its LDP Hellos, and MUST set the "TR" field to announce its
   preference for either IPv4 LDPoIPv4 or
   IPv6 LDPoIPv6 transport connection. The
   default preference is IPv6. LDPoIPv6.

   Upon receiving the hello message with this TLV, messages from the neighbor, a dual-stack capable
   receiving Dual-stack
   LSR MUST do check for the following: presence of "Dual-stack capability" TLV and
   take appropriate actions as follows:

     1. If it understands the TLV, "Dual-stack capability" TLV is present and if neighbor's remote preference
        does not match with the local preference, then it discards the LSR MUST
        discard the hello
        (and no adjacency is formed) message and logs log an error.

     2.

        If it understands LDP session was already in place, then LSR MUST send a fatal
        Notification message with status code [Transport Connection
        mismatch, IANA allocation TBD] and reset the TLV, session.

     2. If "Dual-stack capability" TLV is present, and if neighbor's remote
        preference matches with the local preference, then:

          a) If TR=0 (IPv4), TR=0100 (LDPoIPv4), 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), TR=0110 (LDPoIPv6), 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 using IPv6 TCP
             connection. transport address
             as defined in section 2.5.2 of RFC 5036.

     3. If it does not understand the TLV, then it MUST silently
        discard this "Dual-stack capability" TLV is NOT present, and process the rest of
          a) Only IPv4 hellos are received, then the Hello message.

   If an neighbor is deemed
             as a legacy IPv4-only LSR receives (supporting Single-stack LDP),
             hence, an LDPoIPv4 session SHOULD be established (similar
             to that of 2a above).

             However, if IPv6 hellos are also received at any time from
             that neighbor, then the hello neighbor is deemed as a non-
             compliant Dual-stack LSR (similar to that of 3c below),
             resulting in any established LDPoIPv4 session being reset
             and a fatal Notification message without the "IPv4orIPv6
   Transport Preference" TLV, being sent (with status
             code of 'Dual-Stack Non-Compliance', IANA allocation TBD).

          b) Only IPv6 hellos are received, then it MUST proceed with the neighbor is deemed
             as an IPv6-only LSR (supporting Single-stack LDP) and
             LDPoIPv6 session
   establishment using single-stack rules, SHOULD be established (similar to that of
             2b above).

             However, if IPv4 hellos are also received at any time from
             that neighbor, then the neighbor is deemed as per section 2.5.2 a non-
             compliant Dual-stack LSR (similar to that of RFC
   5036. 3c below),
             resulting in any established LDPoIPv6 session being reset
             and a fatal Notification message being sent (with status
             code of 'Dual-Stack Non-Compliance', IANA allocation TBD).

          c) Both IPv4 and IPv6 hellos are received, then the neighbor
             is deemed as a non-compliant Dual-stack neighbor, and is
             not allowed to have any LDP session.

   An LSR MUST convey the same transport connection preference ("TR"
   field)
   field value) 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 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 this new Capability TLV could be a new Flag
   value in LDP Hello message, however, it will get used even in a single-stack
   Single-stack IPv6 scenarios LDP networks and linger on forever, even though dual-stack
   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 Dual-stack LDP enabled interface(s) or
     via two (or more) single-stack Single-stack LDP enabled interfaces;
   - a single-stack Single-stack LDP enabled interface is converted to a dual-stack Dual-stack
     LDP enabled interface (e.g. figure 1) on either LSR;
   - an additional single-stack Single-stack or dual-stack 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 setting up
   the LDP session in preferred AFI 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 Dual-stack LDP enabled interfaces being converted into
   a single-stack 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 MUST be
   reset. Otherwise, the LDP session SHOULD MUST stay intact.

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

7. Address Binding Distribution

   If an LSR is

   LSRs by definition can be enabled with dual-stack LDP (i.e. for Dual-stack LDP in both IPv4 and
   IPv6 globally and/or
   per peer so as to exchange the address families) and label bindings for any (discovered or targeted) peer, then
   it MUST advertise (via ADDRESS message) its local both
   IPv4 and IPv6
   addresses to that peer by default, address-families, independent of the transport
   connection (address family) used for LDPoIPv4 or LDPoIPV6
   session between them.

   However, there might be some legacy LSRs that peering.

   If an LSR, are fully compliant
   with this specification, is enabled with
   single-stack LDP (i.e. LDP in either IPv6 or IPv4 address family) RFC 5036 for any (discovered or targeted) peer, then it IPv4, but non-compliant for IPv6 (say, section
   3.5.5.1 of RFC 5036), causing them to reset the session upon
   receiving IPv6 address bindings or IPv6 FEC (Prefix) label bindings.
   This is somewhat undesirable, as clarified further Appendix A.1 and
   A.2.

   To help maintain backward compatibility (accommodate IPv4-only LDP
   implementations that may not be compliant with RFC 5036 section
   3.5.5.1), this specification requires that an LSR MUST NOT send any
   IPv6 bindings to a peer if peer has been determined as a legacy LSR.

   The 'Dual-stack capability' TLV, which is defined in section 6.1.1,
   is also used to determine if a peer is a legacy (IPv4-only Single-
   stack) LSR or not.

7.1. Address Distribution

   An LSR MUST NOT advertise (via ADDRESS message) any IPv4-mapped IPv6
   addresses (defined in section 2.5.5.2 of [RFC4291]), and ignore such
   addresses, if ever received. Please see Appendix A.3.

   If an LSR is enabled with Dual-stack LDP for a peer and

     1. Is NOT able to find the Dual-stack capability TLV in the
        incoming IPv4 LDP hello messages from that peer, then the LSR
        MUST NOT advertise its local IPv6 Addresses to the peer.

     2. Is able to find the Dual-stack capability in the incoming IPv4
        (or IPv6) LDP Hello messages from that peer, then it MUST
        advertise (via ADDRESS message) its local IPv4 and IPv6
        addresses to that peer.

     3. Is NOT able to find the Dual-stack capability in the incoming
        IPv6 LDP Hello messages, then it MUST advertise (via ADDRESS
        message) only its local IPv6 addresses to that peer.

        The last point helps to maintain forward compatibility (no need
        to require this TLV in case of IPv6 Single-stack LDP).

   If an LSR is enabled with Single-stack LDP for any peer, then it
   MUST advertise (via ADDRESS message) its local IP addresses as per
   the enabled address
   family by default, family, and SHOULD accept a received Address message messages
   containing both IPv4 and IPv6 addresses.

8. IP addresses as per the enabled address family.

7.2. 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

   If an LSR enabled with IPv4-only Dual-stack LDP implementations) in light of section 3.4.1.1 of
   RFC5036, as rationalized for a peer and

     1. Is NOT able to find the Dual-stack capability TLV in the Appendix section A.1 later, this
   document specifies
        incoming IPv4 LDP hello messages from that -

     1. An peer, then the LSR
        MUST NOT send a label mapping message with a FEC TLV
        containing two or more Prefix FEC Elements of different advertise IPv6 FEC-label bindings to the peer.

     2. Is able to find the Dual-stack capability in the incoming IPv4
        (or IPv6) LDP Hello messages from that peer, then it MUST
        advertise FEC-Label bindings for both IPv4 and IPv6 address
        families. This means
        families to that a FEC TLV in peer.

     3. Is NOT able to find the label mapping
        message must contain all Dual-stack capability in the Prefix FEC Elements belonging incoming
        IPv6 LDP Hello messages, then it MUST advertise FEC-Label
        bindings for IPv6 address families to that peer.

        The last point helps to maintain forward compatibility (no need
        to require this TLV for IPv6 address family or IPv4 address family, but not both. Single-stack LDP).

   If an LSR is enabled with dual-stack LDP (i.e. Single-stack LDP in both IPv4 and
   IPv6 address families) for any peer, then it
   MUST advertise the FEC-
   Label (via ADDRESS message) FEC-Label bindings for both IPv4 the
   enabled address family, and IPv6 accept FEC-Label bindings for the
   enabled address families to that peer.
   However, an family.

   An LSR MAY further 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. basis to a peer.

   If an LSR is configured to move change an interface or peer from single- Single-
   stack (IPv6 or IPv4 address family) to dual-stack LDP (IPv6 and IPv4
   address families), to Dual-stack LDP, then an LSR SHOULD use Typed Wildcard
   FEC procedures [RFC5918] to request the FEC-label label bindings for the
   enabled address family. This helps to relearn the FEC-label label bindings
   that may have been discarded before without resetting the peering.

9. session.

8. 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 received 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.

10.

9. 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.

10. IANA Considerations

   This document defines a new optional parameter for the LDP Hello
   Message and two new status codes for the LDP Notification Message.

   The type 'Dual-Stack capability' parameter requires a code point from the
   TLV Type Name Space.  [RFC5036] partitions the TLV Type Name Space
   into 3 regions:  IETF Consensus region, First Come First Served
   region, and Private Use region.  The authors recommend that a code
   point from the IETF Consensus range be assigned to the 'Dual-Stack
   capability' TLV.

   The 'Transport Connection Mismatch' status code requires a code
   point from the Status Code Name Space.  [RFC5036] partitions the
   Status Code Name Space into 3 regions:  IETF Consensus region, First
   Come First Served region, and Private Use region.  The authors
   recommend that a code needs point from the IETF Consensus range be
   assigned to the 'Transport Connection Mismatch ' status code.

   The 'Dual-Stack Non-Compliance' status code requires a code point
   from the Status Code Name Space.  [RFC5036] partitions the Status
   Code Name Space into 3 regions:  IETF Consensus region, First Come
   First Served region, and Private Use region.  The authors recommend
   that a code point from the IETF Consensus range be assigned by IANA.

12. to the
   'Dual-Stack Non-Compliance' status code.

11. 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] [RFC7321] as well as [RFC5920].

13.

12. 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, Santosh Esale, Danial Johari 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.

13. 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

15.

14. References

15.1.

14.1. 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.

14.2. Informative References

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

   [RFC4835]

   [RFC7321] Manral, V., "Cryptographic Algorithm Implementation
             Requirements for Encapsulating Security Payload (ESP) and
             Authentication Header (AH)", RFC 4835, 7321, 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.

   [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.

Appendix A.

A.1. IPv6 Transition", RFC
             4038, March 2005.

Appendix A.

A.1. LDPv6 and LDPv4 Interoperability Safety Net

   It is not safe to assume that RFC5036 compliant implementations have
   supported handling IPv6 address family (IPv6 FEC label) in Label
   Mapping message all along.

   If a router upgraded with this specification advertised both IPv4
   and IPv6 FECs in the same label mapping message, then an IPv4-only
   peer (not knowing how to process such a message) may abort
   processing the entire label mapping message (thereby discarding even
   the IPv4 label FECs), as per the section 3.4.1.1 of RFC5036.

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

   The change proposed in section 8 of this document provides a good
   safety net and LDPv4 Interoperability Safety Net makes LDPv6 incrementally deployable without making
   any such assumption on the routers' support for IPv6 FEC processing
   in current production networks.

A.2. Accommodating Non-RFC5036-compliant implementations

   It is naive not safe to assume that RFC5036 compliant implementations have
   supported been RFC5036
   compliant in gracefully handling IPv6 address family (IPv6 FEC processing, in particular) Address
   List TLV) in label advertisement Address message all along. And if that assumption turned out

   If a router upgraded with this specification advertised IPv6
   addresses (with or without IPv4 addresses) in Address message, then
   an IPv4-only peer (not knowing how to be process such a message) may
   not true, then follow section 3.4.1.1 3.5.5.1 of RFC5036 would cause LSRs to
   abort processing the entire label mapping message RFC5036, and generate an
   error. tear down the LDP
   session.

   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.

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

   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.

A.4. 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
   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.

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