OSPF Working Group                                            Alex Zinin
Internet Draft                                                   Alcatel
Expiration Date: December 2006                            Barry Friedman
File name: draft-ietf-ospf-lls-01.txt                          Abhay Roy
                                                             Liem Nguyen
                                                             Derek Yeung
                                                           Cisco Systems
                                                               June 2006

                       OSPF Link-local Signaling

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Copyright Notice

   Copyright (C) The Internet Society (2006).


   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 which need to exchange arbitrary data.  This memo
   describes a backward-compatible technique to perform link-local
   signaling, i.e., exchange arbitrary data on a link.

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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 which may not be desirable and may cause backward
   compatibility issues. This document describes how to exchange data
   using standard OSPF packet types.

1.1  Conventions Used In This Document

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC2119 [KEY].

2. Proposed solution

   To perform link-local signaling (LLS), OSPF routers add a special
   data block at 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 OSPF
   packet, but is included in the IPv4/IPv6 packet length. Figure 1
   illustrates how the LLS data block is attached.

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

   This memo does not specify how the data transmitted by the LLS
   mechanism should be interpreted by OSPF routers. The interface
   between OSPF LLS component and its clients is implementation

2.1. Options Field

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

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

                        Figure 2a: OSPFv2 Options field

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           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 is only set in Hello and DBD packets.

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 of the entire
   contents of the LLS block.

   The 16-bit LLS Data Length field contains the length (in 32-bit
   words) of the LLS block including the header and payload.
   Implementations MUST NOT use the Length field in the IP packet
   header to determine the length of the LLS data block.

   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 and the LLS block
   will contain a cryptographic authentication TLV (see Section 2.6).

   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).

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2.3. LLS TLVs

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

   The type field contains the TLV ID which is unique for each type of
   TLVs. The Length field contains the length of the Value field (in
   bytes) that 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 32-bit boundary, but padding
   bytes are not included in TLV Length field (though it is included in
   the LLS Data Length field of the LLS block header).

2.5. Extended Options TLV

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

   Bits in the Value field do not have any semantics from the point of
   view of LLS mechanism. This field MAY be used to announce some OSPF
   capabilities that are link-specific. Also, other OSPF extensions MAY
   allocate bits in the bit vector to perform boolean link-local

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

   The value of the type field in EO-TLV is 1.

   EO-TLV MUST only appear once in the LLS data block.

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     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                        |

                        Figure 5: Format of EO TLV

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

   The Extended Options bits are defined in Section 3.

2.6. 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 be
   included in the LLS block when the cryptographic (MD5) 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 that used for the main OSPFv2 packet. The cryptographic
   sequence number is included in the TLV and MUST be the same as the
   one in the main OSPFv2 packet for the LLS block to be considered

   The TLV is constructed as shown 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

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

   The Length field in the header contains the length of the data
   portion of the TLV that includes 4 bytes for the Sequence Number and
   the length of the message digest (MD5) block for the whole LLS block
   in bytes (this will always be 16 bytes for MD5). So AuthLen field
   will have value of 20.

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   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.

   The AuthData contains the message digest calculated for the LLS data

   The CA-TLV MUST only appear once in the the LLS block. Also, when
   present, this TLV SHOULD be the last TLV in the LLS block.

3. IANA Considerations

   LLS TLV types are maintained by the IANA.  Extensions to OSPF which
   require a new LLS TLV type MUST be reviewed by an designated expert
   from the routing area.

   Following the policies outlined in [IANA], LLS type values in the
   range of 0-32767 are allocated through an IETF Consensus action and
   LLS type values in the range of 32768-65536 are reserved for private
   and experimental use.

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

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

     *[RFCNNNN] refers to the RFC number-to-be for this document.
     + Cryptographic Authentication TLV is only defined for OSPFv2

   This document also assigns the following bits for the Extended
   Options bits field in the EO-TLV outlined in Section 2.5:

     Extended Options Bit      Name                        Reference
       0x00000001              LSDB Resynchronization (LR) [OOB]
       0x00000002              Restart Signal (RS-bit)     [RESTART]

   Other Extended Options bits will be allocated through an IETF
   consensus action.

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4. Compatibility Issues

   The modifications to OSPF packet formats are compatible with standard
   OSPF because LLS-incapable routers will not consider the extra data
   after the packet; i.e., the LLS data block will be ignored by routers
   which do not support the LLS extension.

5. Security Considerations

   The described technique provides the same level of security as OSPF
   protocol by allowing LLS data to be authenticated (see Section 2.6
   for more details).

   OSPFv3 has IPSec authentication built in. There are AH/ESP techniques
   which operate on the whole OSPFv3 payload. So we do not need a
   separate cryptographic TLV for OSPFv3.

6. Acknowledgements

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

7. References

7.1 Normative References

   [OSPFV2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
   [OSPFV3] R. Coltun, D. Ferguson and J.  Moy,  "OSPF  for  IPv6",
            RFC 2740, December 1999.
   [KEY] Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.
   [IANA] Narten, T., and H. Alvestrand, "Guidelines for Writing an IANA
          Considerations Section in RFCs", RFC 2434, October 1998.

7.2 Informative References

   [OOB] Zinin, A., Roy, A. and L. Nguyen,
         "OSPF Out-of-band LSDB resynchronization",
         Work in progress, September 2004.

   [RESTART] Zinin, A., Roy, A. and L. Nguyen, "OSPF Restart Signaling",
             Work in progress, September 2004.

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8. Author Information

   Alex Zinin                                   Abhay Roy
   Alcatel                                      Cisco Systems
   Sunnyvale, CA                                170 W. Tasman Dr.
   USA                                          San Jose,CA 95134
   E-mail: zinin@psg.com                        USA
                                                E-mail: akr@cisco.com
   Barry Friedman
   Cisco Systems                                Derek M. Yeung
   170 W. Tasman Dr.                            Cisco Systems
   San Jose,CA 95134                            170 W. Tasman Dr.
   USA                                          San Jose,CA 95134
   E-mail: friedman@cisco.com                   USA
                                                E-mail: myeung@cisco.com
   Liem Nguyen
   Cisco Systems
   170 W. Tasman Dr.
   San Jose,CA 95134
   E-mail: lhnguyen@cisco.com

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