OSPF Link-Local Signaling
RFC 5613

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.

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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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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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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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   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.

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   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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   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.

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   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.

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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.

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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.

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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

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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

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