    Network Working Group                                           A. Zinin
    Request for Comments: 5613                                Alcatel-Lucent
    Obsoletes: 4813                                                   A. Roy
    Category: Standards Track                                      L. Nguyen
                                                               Cisco Systems
                                                                 B. Friedman
                                                                Google, Inc.
                                                                    D. Yeung
                                                               Cisco Systems
                                                                 August 2009

                           OSPF Link-Local Signaling

    Abstract

       OSPF is a link-state intra-domain routing protocol.  OSPF routers
       exchange information on a link using packets that follow a well-
       defined fixed format.  The format is not flexible enough to enable
       new features that need to exchange arbitrary data.  This document
       describes a backward-compatible technique to perform link-local
       signaling, i.e., exchange arbitrary data on a link.  This document
       replaces the experimental specification published in RFC 4813 to
       bring it on the Standards Track.

    Status of This Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    Copyright Notice

       Copyright (c) 2009 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 (http://trustee.ietf.org/license-info).
       Please review these documents carefully, as they describe your rights
       and restrictions with respect to this document.

    Zinin, et al.               Standards Track                     [Page 1]

    RFC 5613               OSPF Link-Local Signaling             August 2009

    Table of Contents

       1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
         1.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  2
       2.  Proposed Solution  . . . . . . . . . . . . . . . . . . . . . .  3
         2.1.  L-Bit in Options Field . . . . . . . . . . . . . . . . . .  4
         2.2.  LLS Data Block . . . . . . . . . . . . . . . . . . . . . .  4
         2.3.  LLS TLVs . . . . . . . . . . . . . . . . . . . . . . . . .  5
         2.4.  Extended Options and Flags TLV . . . . . . . . . . . . . .  5
         2.5.  Cryptographic Authentication TLV (OSPFv2 ONLY) . . . . . .  6
         2.6.  Private TLVs . . . . . . . . . . . . . . . . . . . . . . .  7
       3.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
       4.  Compatibility Issues . . . . . . . . . . . . . . . . . . . . .  9
       5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
       6.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
         6.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
         6.2.  Informative References . . . . . . . . . . . . . . . . . . 10
       Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 11
       Appendix B.  Changes from RFC 4813 . . . . . . . . . . . . . . . . 11

    1.  Introduction

       This document describes an extension to OSPFv2 [OSPFV2] and OSPFv3
       [OSPFV3] allowing additional information to be exchanged between
       routers on the same link.  OSPFv2 and OSPFv3 packet formats are fixed
       and do not allow for extension.  This document proposes appending an
       optional data block composed of Type/Length/Value (TLV) triplets to
       existing OSPFv2 and OSPFv3 packets to carry this additional
       information.  Throughout this document, OSPF will be used when the
       specification is applicable to both OSPFv2 and OSPFv3.  Similarly,
       OSPFv2 or OSPFv3 will be used when the text is protocol specific.

       One potential way of solving this task could be introducing a new
       packet type.  However, that would mean introducing extra packets on
       the network that may not be desirable and may cause backward
       compatibility issues.  This document describes how to exchange data
       using standard OSPF packet types.

    1.1.  Requirements Notation

       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 [KEY].

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    RFC 5613               OSPF Link-Local Signaling             August 2009

    2.  Proposed Solution

       To perform link-local signaling (LLS), OSPF routers add a special
       data block to the end of OSPF packets or right after the
       authentication data block when cryptographic authentication is used.
       The length of the LLS block is not included into the length of the
       OSPF packet, but is included in the IPv4/IPv6 packet length.  Figure
       1 illustrates how the LLS data block is attached.

       +---------------------+ --              --  +---------------------+
       | IP Header           | ^               ^   | IPv6 Header         |
       | Length = HL+X+Y+Z   | | Header Length |   | Length = HL+X+Y     |
       |                     | v               v   |                     |
       +---------------------+ --              --  +---------------------+
       | OSPF Header         | ^               ^   | OSPFv3 Header       |
       | Length = X          | |               |   | Length = X          |
       |.....................| | X             | X |.....................|
       |                     | |               |   |                     |
       | OSPFv2 Data         | |               |   | OSPFv3 Data         |
       |                     | v               v   |                     |
       +---------------------+ --              --  +---------------------+
       |                     | ^               ^   |                     |
       | Authentication Data | | Y             | Y |  LLS Data           |
       |                     | v               v   |                     |
       +---------------------+ --              --  +---------------------+
       |                     | ^
       |  LLS Data           | | Z
       |                     | v
       +---------------------+ --

                   Figure 1: LLS Data Block in OSPFv2 and OSPFv3

       The LLS block MAY be attached to OSPF Hello and Database Description
       (DD) packets.  The LLS block MUST NOT be attached to any other OSPF
       packet types on generation and MUST be ignored on reception.

       The data included in the LLS block attached to a Hello packet MAY be
       used for dynamic signaling since Hello packets may be sent at any
       time.  However, delivery of LLS data in Hello packets is not
       guaranteed.  The data sent with DD packets is guaranteed to be
       delivered as part of the adjacency forming process.

       This document does not specify how the data transmitted by the LLS
       mechanism should be interpreted by OSPF routers.  As routers that do
       not understand LLS may receive these packets, changes made due to LLS
       block TLV's do not affect the basic routing when interacting with
       non-LLS routers.

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    RFC 5613               OSPF Link-Local Signaling             August 2009

    2.1.  L-Bit in Options Field

       A new L-bit (L stands for LLS) is introduced into the OSPF Options
       field (see Figures 2a and 2b).  Routers set the L-bit in Hello and DD
       packets to indicate that the packet contains an LLS data block.  In
       other words, the LLS data block is only examined if the L-bit is set.

                 +---+---+---+---+---+---+---+---+
                 | * | O | DC| L |N/P| MC| E | * |
                 +---+---+---+---+---+---+---+-+-+

                  Figure 2a: OSPFv2 Options Field

       0                   1                       2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7  8  9  0  1  2  3
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+--+--+--+--+--+
       | | | | | | | | | | | | | | |L|AF|*|*|DC| R| N|MC| E|V6|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+--+--+--+--+--+

                  Figure 2b: OSPFv3 Options Field

       The L-bit MUST NOT be set except in Hello and DD packets that contain
       an LLS block.

    2.2.  LLS Data Block

       The data block used for link-local signaling is formatted as
       described below (see Figure 3 for illustration).

       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 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Checksum           |       LLS Data Length         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                           LLS TLVs                            |
       .                                                               .
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 3: Format of LLS Data Block

       The Checksum field contains the standard IP checksum for the entire
       contents of the LLS block.  Before computing the checksum, the
       checksum field is set to 0.  If the checksum is incorrect, the OSPF
       packet MUST be processed, but the LLS block MUST be discarded.

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    RFC 5613               OSPF Link-Local Signaling             August 2009

       The 16-bit LLS Data Length field contains the length (in 32-bit
       words) of the LLS block including the header and payload.

       Note that if the OSPF packet is cryptographically authenticated, the
       LLS data block MUST also be cryptographically authenticated.  In this
       case, the regular LLS checksum is not calculated, but is instead set
       to 0.

       The rest of the block contains a set of Type/Length/Value (TLV)
       triplets as described in Section 2.3.  All TLVs MUST be 32-bit
       aligned (with padding if necessary).

    2.3.  LLS TLVs

       The contents of an LLS data block are constructed using TLVs.  See
       Figure 4 for the TLV format.

       The Type field contains the TLV ID, which is unique for each type of
       TLV.  The Length field contains the length of the Value field (in
       bytes).  The Value field is variable and contains arbitrary data.

       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 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Type               |           Length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                             Value                             .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 4: Format of LLS TLVs

       Note that TLVs are always padded to a 32-bit boundary, but padding
       bytes are not included in the TLV Length field (though they are
       included in the LLS Data Length field in the LLS block header).
       Unrecognized TLV types are ignored.

    2.4.  Extended Options and Flags TLV

       This subsection describes a TLV called the Extended Options and Flags
       (EOF) TLV.  The format of the EOF-TLV is shown in Figure 5.

       Bits in the Value field do not have any semantics from the point of
       view of the LLS mechanism.  Bits MAY be allocated to announce OSPF
       link-local capabilities.  Bits MAY also be allocated to perform
       boolean link-local signaling.

    Zinin, et al.               Standards Track                     [Page 5]

    RFC 5613               OSPF Link-Local Signaling             August 2009

       The length of the Value field in the EOF-TLV is 4 bytes.

       The value of the Type field in the EOF-TLV is 1.  The EOF-TLV MUST
       only appear once in the LLS data block.

       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 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             1                 |            4                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                  Extended Options and Flags                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                            Figure 5: Format of the EOF-TLV

       Currently, [OOB] and [RESTART] use bits in the Extended Options field
       of the EOF-TLV.

       The Extended Options and Flags bits are defined in Section 3.

    2.5.  Cryptographic Authentication TLV (OSPFv2 ONLY)

       This document defines a special TLV that is used for cryptographic
       authentication (CA-TLV) of the LLS data block.  This TLV MUST only be
       included in the LLS block when cryptographic authentication is
       enabled on the corresponding interface.  The message digest of the
       LLS block MUST be calculated using the same key and authentication
       algorithm as used for the OSPFv2 packet.  The cryptographic sequence
       number is included in the TLV and MUST be the same as the one in the
       OSPFv2 authentication data for the LLS block to be considered
       authentic.

       The TLV is constructed as shown in Figure 6.

       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 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              2                |         AuthLen               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Sequence Number                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                           AuthData                            .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 6: Format of Cryptographic Authentication TLV

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    RFC 5613               OSPF Link-Local Signaling             August 2009

       The value of the Type field for the CA-TLV is 2.

       The Length field in the header contains the length of the data
       portion of the TLV including 4 bytes for Sequence Number and the
       length of the message digest block for the whole LLS block in bytes.

       The Sequence Number field contains the cryptographic sequence number
       that is used to prevent simple replay attacks.  For the LLS block to
       be considered authentic, the Sequence Number in the CA-TLV MUST match
       the Sequence Number in the OSPFv2 packet header Authentication field
       (which MUST be present).  In the event of Sequence Number mismatch or
       Authentication failure, the whole LLS block MUST be ignored.

       The CA-TLV MUST NOT appear more than once in the LLS block.  Also,
       when present, this TLV MUST be the last TLV in the LLS block.  If it
       appears more than once, only the first occurrence is processed and
       any others MUST be ignored.

       The AuthData field contains the message digest calculated for the LLS
       data block up to the CA-TLV AuthData field (i.e., excludes the CA-TLV
       AuthData).

       The CA-TLV is not applicable to OSPFv3 and it MUST NOT be added to
       any OSPFv3 packet.  If found on reception, this TLV MUST be ignored.

    2.6.  Private TLVs

       LLS type values in the range of 32768-65536 are reserved for private
       use.  The first four octets of the Value field MUST be the private
       enterprise code [ENTNUM].  This allows multiple vendor private
       extensions to coexist in a network.

    3.  IANA Considerations

       This document uses the registry that was originally created in
       [RFC4813].  IANA updated the following registry to point to this
       document instead:

       o  "Open Shortest Path First (OSPF) Link-Local Signalling (LLS) -
          Type/Length/Value Identifiers (TLV)"

       IANA allocated L-bit in the "OSPFv2 Options Registry" and "OSPFv3
       Options Registry" as per Section 2.1.

       LLS TLV types are maintained by the IANA.  Extensions to OSPF that
       require a new LLS TLV type MUST be reviewed by a Designated Expert
       from the routing area.

    Zinin, et al.               Standards Track                     [Page 7]

    RFC 5613               OSPF Link-Local Signaling             August 2009

       The criteria for allocating LLS TLVs are:

       o  LLS should not be used for information that would be better suited
          to be advertised in a link-local link state advertisement (LSA).

       o  LLS should be confined to signaling between direct neighbors.

       o  Discretion should be used in the volume of information signaled
          using LLS due to the obvious MTU and performance implications.

       Following the policies outlined in [IANA], LLS type values in the
       range of 0-32767 are allocated through an IETF Review and LLS type
       values in the range of 32768-65535 are reserved for private use.

       This document assigns the following LLS TLV types in OSPFv2/OSPFv3.

       TLV Type    Name                                      Reference
       0           Reserved
       1           Extended Options and Flags                [RFC5613]
       2           Cryptographic Authentication+             [RFC5613]
       3-32767     Reserved for assignment by the IANA
       32768-65535 Private Use

       + Cryptographic Authentication TLV is only defined for OSPFv2

       IANA renamed the sub-registry from "LLS Type 1 Extended Options" to
       "LLS Type 1 Extended Options and Flags".

       This document also assigns the following bits in the EOF-TLV outlined
       in Section 2.5:

       Bit                     Name                        Reference
       0x00000001              LSDB Resynchronization (LR) [RFC4811]
       0x00000002              Restart Signal (RS-bit)     [RFC4812]

       Future allocation of Extended Options and Flags bits MUST be reviewed
       by a Designated Expert from the routing area.

    Zinin, et al.               Standards Track                     [Page 8]

    RFC 5613               OSPF Link-Local Signaling             August 2009

    4.  Compatibility Issues

       The modifications to OSPF packet formats are compatible with standard
       OSPF since OSPF routers not supporting LLS will ignore the LLS data
       block after the OSPF packet or cryptographic message digest.  As of
       this writing, there are implementations deployed with [RFC4813]-
       compliant software.  Routers not implementing [RFC4813] ignore the
       LLS data at the end of the OSPF packet.

       Careful consideration should be given to carrying additional LLS
       data, as it may affect the OSPF adjacency bring-up time due to
       additional propagation delay and/or processing time.

    5.  Security Considerations

       Security considerations inherited from OSPFv2 are described in
       [OSPFV2].  This technique provides the same level of security as the
       basic OSPFv2 protocol by allowing LLS data to be authenticated using
       the same cryptographic authentication that OSPFv2 uses (see
       Section 2.5 for more details).

       Security considerations inherited from OSPFv3 are described in
       [OSPFV3] and [OSPFV3AUTH].  OSPFv3 utilizes IPsec for authentication
       and encryption.  With IPsec, the AH (Authentication Header), ESP
       (Encapsulating Security Payload), or both are applied to the entire
       OSPFv3 payload including the LLS block.

    6.  References

    6.1.  Normative References

       [IANA]        Narten, T. and H. Alvestrand, "Guidelines for Writing
                     an IANA Considerations Section in RFCs", BCP 26,
                     RFC 5226, May 2008.

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

       [OSPFV2]      Moy, J., "OSPF Version 2", STD 54, RFC 2328,
                     April 1998.

       [OSPFV3]      Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
                     for IPv6", RFC 5340, July 2008.

       [OSPFV3AUTH]  Gupta, M. and N. Melam, "Authentication/Confidentiality
                     for OSPFv3", RFC 4552, June 2006.

    Zinin, et al.               Standards Track                     [Page 9]

    RFC 5613               OSPF Link-Local Signaling             August 2009

    6.2.  Informative References

       [ENTNUM]      IANA, "PRIVATE ENTERPRISE NUMBERS",
                     http://www.iana.org.

       [OOB]         Nguyen, L., Roy, A., and A. Zinin, "OSPF Out-of-Band
                     Link State Database (LSDB) Resynchronization",
                     RFC 4811, March 2007.

       [RESTART]     Nguyen, L., Roy, A., and A. Zinin, "OSPF Restart
                     Signaling", RFC 4812, March 2007.

       [RFC4813]     Friedman, B., Nguyen, L., Roy, A., Yeung, D., and A.
                     Zinin, "OSPF Link-Local Signaling", RFC 4813,
                     March 2007.

    Zinin, et al.               Standards Track                    [Page 10]

    RFC 5613               OSPF Link-Local Signaling             August 2009

    Appendix A.  Acknowledgements

       The authors would like to acknowledge Russ White, Acee Lindem, and
       Manral Vishwas for their review of this document.

    Appendix B.  Changes from RFC 4813

       This section describes the substantive change from [RFC4813].

       o  Added OSPFv3 support

       o  Private TLVs MUST use private enterprise code

       o  Clarified requirement levels at several places

       o  Changed from Experimental to Standards Track

    Zinin, et al.               Standards Track                    [Page 11]

    RFC 5613               OSPF Link-Local Signaling             August 2009

    Authors' Addresses

       Alex Zinin
       Alcatel-Lucent
       Singapore

       EMail: alex.zinin@alcatel-lucent.com

       Abhay Roy
       Cisco Systems
       170 West Tasman Drive
       San Jose, CA  95134
       USA

       EMail: akr@cisco.com

       Liem Nguyen
       Cisco Systems
       170 West Tasman Drive
       San Jose, CA  95134
       USA

       EMail: lhnguyen@cisco.com

       Barry Friedman
       Google, Inc.
       1600 Amphitheatre Parkway
       Mountain View, CA  94043
       USA

       EMail: barryf@google.com

       Derek Yeung
       Cisco Systems
       170 West Tasman Drive
       San Jose, CA  95134
       USA

       EMail: myeung@cisco.com

    Zinin, et al.               Standards Track                    [Page 12]