MPLS Working Group                                       Vishwas Manral
Internet Draft                                          IPInfusion Inc.
Updates: 5036 (if approved)
Intended status: Standards Track                          Rajiv Papneja
Expires: September 2011                                         Isocore

                                                            Rajiv Asati

                                                       Carlos Pignataro

                                                           May 12, 17, 2011

                          Updates to LDP for IPv6

Status of this Memo

   This Internet-Draft is submitted to IETF 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

   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 November 12, 17, 2011.

Copyright Notice

   Copyright (c) 2011 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
   ( 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.


   The Label Distribution Protocol (LDP) specification defines
   procedures to exchange label bindings over either IPv4, 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........................................3
   2. Specification Language.........................................4
   3. LSP Mapping....................................................5
   4. LDP Identifiers................................................6
   5. Peer Discovery.................................................6
      5.1. Basic Discovery Mechanism.................................6
      5.2. Extended Discovery Mechanism..............................7
   6. LDP Session Establishment and Maintenance......................8
      6.1. Transport connection establishment........................8
      6.2. Maintaining Hello Adjacencies.............................9
      6.3. Maintaining LDP Sessions.................................10
   7. Label Distribution............................................10
   8. IANA Considerations...........................................10
   9. Security Considerations.......................................11
   10. Acknowledgments..............................................11
   11. References...................................................12
      11.1. Normative References....................................12
      11.2. Informative References..................................12
   Author's Addresses...............................................13

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 deficiencies in
   regards to IPv6 usage:

   1) LSP mapping: No rule defined 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 multicast
      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 Label exchange: No rule for advertising IPv4 or/and IPv6 FEC-
      label bindings over an LDP session

   6) LDP TTL security: No rule for built-in Generalized TTL Security
      Mechanism (GTSM) in LDP

   This document addresses the above deficiencies by specifying the
   desired behavior/rules/details. It also clarifies the topology
   scenarios in section 1.1.

   Note that this document updates RFC5036.

1.1. Topology Scenarios

   The following scenarios in which the LSRs may be inter-connected via
   one or more dual-stack interfaces (figure 1), or two or more single-
   stack interfaces (figure 2 and figure 3) become quite relevant to
   consider while addressing the deficiencies highlighted in section 1.


            Figure 1 LSRs connected via a Dual-stack Interface


          Figure 2 LSRs connected via two single-stack Interfaces

                       IPv4                 IPv6

           Figure 3 LSRs connected via a single-stack Interface

   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 as well as IPv6 LDP, even though
   the IPv4 LDP session may already be established between the LSRs.

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

2. Specification Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].


   LDP      - Label Distribution Protocol

   LDPv4    - LDP for enabling IPv4 MPLS forwarding

   LDPv6    - Label Distribution Protocol using LDP for enabling IPv6 MPLS forwarding
   LDPoIPv4 - LDP over IPv4 transport address
          family session

   LDPoIPv6 - LDP over IPv6 transport session

   FEC      - Forwarding Equivalence Class

   TLV      - Type Length Value

   LSR      - Label Switch Router

   LSP      - Label Switched Path

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."

   Suffice to say, this rule is correct for IPv4, but not for IPv6,
   since an IPv6 router may not have any /32 address.

   This document proposes to modify this rule by also including a /128
   address (for IPv6). In fact, it should be reasonable to just 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."

   While the above rule mentions 'Address Prefix FEC', it is also
   applicable to 'Typed WildCard prefix FEC' [RFC5918].

   Additionally, it is desirable that a packet is forwarded to an LSP
   of an egress router, only if LSP's address-family matches with that
   of the LDP hello adjacency on the next-hop interface.

4. LDP Identifiers

   Section 2.2.2 of [RFC5036] specifies formulating at least one LDP
   Identifier, however, it doesn't provide any consideration in case of
   IPv6 (with or without dual-stacking). Additionally, section 2.5.2 of
   [RFC5036] implicitly prohibits using the same label space for both
   IPv4 and IPv6 FEC-label bindings.

   The first four octets of the LDP identifier, the 32-bit LSR Id,
   identify the LSR and is a globally unique value. This is regardless
   of the address family used for the LDP session. In other words, this
   document preserves the usage of 32-bit LSR Id on an IPv6 only LSR.

     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 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.

   The first sentence of last paragraph of Section 2.5.2 of [RFC5036]
   is qualified per address family and therefore updated to the
   following: "For a given address family over which a Hello is sent,
   and a given label space, an LSR MUST advertise the same transport
   address." This rightly enables the per-platform label space to be
   shared between IPv4 and IPv6.

   In summary, this document not only allows the usage of a common LDP
   identifier i.e. same LSR-Id, but also the common Label space id for
   both IPv4 and IPv6 on a dual-stack LSR.

   This document reserves as the LSR-Id, and prohibits its

5. Peer Discovery

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
   sends 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

   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 for IPv6
   LDP Link Hellos. An LDP Hello packet received on any of the other
   addresses must be dropped.

   Also, the 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 specified in Generalized TTL Security Mechanism
   (GTSM)[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. enabled with both IPv4 and IPv6 LDP), then the LSR must
   periodically send both IPv4 and IPv6 LDP Link Hellos (using the same
   LDP Identifier per section 4) and must separately maintain the Hello
   adjacency for IPv4 and IPv6 on that interface.

   Needless to say, the IPv4 and IPv6 LDP Link Hellos must carry the
   same LDP identifier (assuming per-platform label space usage).

5.2. Extended Discovery Mechanism

   Suffice to say, the extended discovery mechanism (defined in section
   2.4.2 of [RFC5036]) doesn't require any additional IPv6 specific
   consideration, since the targeted LDP Hellos are sent to a pre-
   configured destination IP address.

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-sections discuss the LDP consideration for IPv6
   and/or dual-stacking in the context of session establishment and

6.1. Transport connection establishment

   Section 2.5.2 of [RFC5036] specifies the use of an optional
   transport address object (TLV) in LDP Link 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 Hello
   adjacencies for both IPv4 and IPv6 whether over a single interface
   or multiple interfaces.

   This document specifies that:

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

     - An LSR should accept the Hello message that contains both IPv4
        and IPv6 transport address optional objects, but use only the
        transport address whose address family is the same as that of
        the IP packet carrying Hello.

     - An LSR must send separate Hellos (each containing either IPv4
        or IPv6 transport address optional object) for each IP address-
        family, if LDP was enabled for both IP address-families.

     - 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 should be established, even if
        there are two Hello adjacencies (one for IPv4 and another for
        IPv6). This is independent of whether the Hello Adjacencies are
        created over a single interface (scenarios 1 in section 1.1) or
        multiple interfaces (scenario 2 in section 1.1) between two

     - An LSR should prefer the LDP/TCP connection over IPv6 for a new
        LDP session with a remote LSR, if it has both IPv4 and IPv6
        hello adjacencies for the same LDP Identifier (over a dual-
        stack interface, or two or more single-stack IPv4 and IPv6
        interfaces). This applies to the section 2.5.2 of RFC5036.

     - An LSR should prefer the LDP/TCP connection over IPv6 for a new
        LDP session with a remote LSR, if they attempted two TCP
        connections using IPv4 and IPv6 transport addresses

   This document allows an implementation to provide a configuration to
   override the above stated preference from IPv6 to IPv4 on a per-peer
   basis. Suffice to say that, such preference must be set on both

   This document also specifies that the LDP/TCP transport connection
   over IPv6 must follow the GTSM procedures (Section 3 of [RFC5082])
   by default, if the LDP/TCP transport connection is being established
   between the adjacent LSRs (using Basic Discovery, as described in
   section 5.1). This means that the IP Hop Limit field is set to 255
   upon sending, and checked to be 255 upon receipt. The built-in
   inclusion of GTSM automatically protects IPv6 LDP peering session
   from off-link attacks.

6.2. Maintaining Hello Adjacencies

   As outlined in section 2.5.5 of RFC5036, this draft suggests that if
   an LSR has a dual-stack interface, which is enabled with both IPv4
   and IPv6 LDP, then the LSR must periodically send both IPv4 and IPv6
   LDP Link Hellos and must separately maintain the Hello adjacency for
   IPv4 and IPv6 on that interface.

     This ensures successful labeled IPv4 and labeled IPv6 traffic
     forwarding on a dual-stacked interface, as well as successful LDP
     peering using the appropriate transport on a multi-access
     interface (even if there are IPv4-only, IPv6-only and dual-stack
     LSRs connected to that multi-access interface).

6.3. Maintaining LDP Sessions

   Two LSRs maintain a single LDP session between them, as described in
   section 6.1, whether they are connected via a dual-stack LDP enabled
   interface or via two single-stack LDP enabled interfaces. This is
   also true when a single-stack interface is converted to a dual-stack
   interface, or when another interface is added between two LSRs.

   On the other hand, if a dual-stack interface is converted to a
   single-stack interface (by disabling IPv4 or IPv6 routing), then the
   LDP session should be torn down ONLY if the disabled IP version was
   the same as that of the transport connection. 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 and RFC5036.

7. Label Distribution

   This document specifies that an LSR should advertise and receive
   both IPv4 and IPv6 label bindings from and to the peer, only if it
   has valid IPv4 and IPv6 Hello Adjacencies for that peer, as
   specified in section 6.2.

   This means that the LSR must not advertise any IPv6 label bindings
   to a peer over an IPv4 LDP session, if no IPv6 Hello Adjacency
   existed for that peer (and vice versa).

8. IANA Considerations


9. 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].

   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].

10. Acknowledgments

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

   Thanks to Bob Thomas for providing critical feedback to improve this
   document early on. Thanks to Kamran Raza, Eric Rosen, Lizhong Jin,
   Bin Mo, Mach Chen, and Kishore Tiruveedhula for reviewing this
   document. The authors also acknowledge the help of Manoj Dutta and
   Vividh Siddha.

   This document was prepared using

11. References

11.1. 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.

11.2. 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.

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

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

Author's Addresses

   Vishwas Manral
   IP Infusion Inc.,
   1188 E. Arques Ave,
   Sunnyvale, CA, 94089

   Rajiv Papneja
   12359 Sunrise Valley Dr, STE 100
   Reston, VA 20190

   Rajiv Asati
   Cisco Systems, Inc.
   7025 Kit Creek Road
   Research Triangle Park, NC 27709-4987

   Carlos Pignataro
   Cisco Systems, Inc.
   7200 Kit Creek Road
   Research Triangle Park, NC 27709-4987