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Versions: 00 01 02 03 04 05 06 07 08 rfc5613                            
Network Working Group                         Alex Zinin (Cisco Systems)
Internet Draft                            Barry Friedman (Cisco Systems)
Expiration Date: July 2001                     Abhay Roy (Cisco Systems)
File name: draft-ietf-ospf-lls-00.txt        Liem Nguyen (Cisco Systems)
                                                   Derek Yeung (Procket)
                                                           November 2000

                       OSPF Link-local Signaling

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet Drafts are working documents of the Internet Engineering
   Task Force (IETF), its Areas, and its Working Groups. Note that other
   groups may also distribute working documents as Internet Drafts.

   Internet Drafts are draft documents valid for a maximum of six
   months. Internet Drafts may be updated, replaced, or obsoleted by
   other documents at any time. It is not appropriate to use Internet
   Drafts as reference material or to cite them other than as a "working
   draft" or "work in progress".

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   OSPF is a link-state intra-domain routing protocol used in IP
   networks. OSPF routers exchange information on a link using packets
   that follow a well-defined format. The format of OSPF packets is not
   flexible enough to enable applications exchange arbitrary data, which
   may be necessary in certain situations.  This memo describes a
   backward-compatible technique to perform link-local signaling, i.e.,
   exchange arbitrary data on a link.

1 Motivation

   Formats of OSPF [RFC2328] packets are not very flexible to provide an
   acceptable mechanism for opaque data transfer. However, this appears
   to be very useful to allow OSPF routers to do so.  An example where
   such a technique could be used is exchanging some capabilities on a

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INTERNET DRAFT         OSPF Link-local Signaling           November 2000

   link (standard OSPF utilizes Options field in Hello and Exchange
   packets, but there are not so many bits left in it).

   One potential way of solving this task could be introducing a new
   packet type. However, in some situations it may not be desirable, so
   this document describes how to exchange data using standard OSPF
   packet types.

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.
   Like with OSPF cryptographic authentication, the length of the LLS-
   block is not included into the length of OSPF packet, but is included
   in the IP packet length. Figure 1 illustrates how the LLS data block
   is attached.

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

                    Figure 1: Attaching LLS Data Block

   The LLS data block may be attached to OSPF packets of two types---
   type 1 (OSPF Hello), and type-2 (OSPF DBD). Note that only the
   initial DBD packet (with the I bit set) may carry the LLS block. 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 an initial DBD packets is guaranteed

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INTERNET DRAFT         OSPF Link-local Signaling           November 2000

   to be delivered as soon as the adjacency proceeds from ExStart state,
   but this info may not change dynamically, since sending of an initial
   DBD packet will bring the adjacency to ExStart state.

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

2.1 Options Field

   A new bit, called L (L stands for LLS) is introduced to OSPF Options
   field (see Figure 2). The value of the bit is 0x10.  Routers set L
   bit in Hellow and DBD packets to indicate that the packet contains
   LLS data block.

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

                        Figure 2: The Options field

   The L-bit is set only in Hello and DBD packets. It is not set in OSPF
   LSAs and may be used in them for different purposes.

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.

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INTERNET DRAFT         OSPF Link-local Signaling           November 2000

   Implementations should 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 checksum is not calculated and the LLS block will
   contain a cryptographic authentication TLV (see Section 2.4.2).

   The rest of the block contains a set of Type/Length/Value (TLV)
   triplets as described in Section 2.2.  All TLVs must be 32-bit
   aligned (with padding if necessary).

2.3 LLS TLVs

   The contents of LLS data block is constructed using TLVs.  See Figure
   4 for 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).

2.4 Predefined TLV

 2.4.1 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

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INTERNET DRAFT         OSPF Link-local Signaling           November 2000

   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 TBD (temporarily used value
   is 1).

   EO-TLV should 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                 |           Length              |
    |                       Extended Options                        |
                        Figure 5: Format of EO TLV

 2.4.2 Cryptographic Authentication TLV

   This document defines a special TLV that is used for cryptographic
   authentication (CA-TLV) of the LLS data block.  This TLV should be
   inluded in the LLS block when the cryptographic (MD5) authentication
   is enabled on the corresponding inteface.  The message digest of the
   LLS block should be calculated using the same key as that used for
   the main OSPF packet. The cryptographic sequence number is included
   in the TLV and must be the same as the one in the main OSPF packet
   for the LLS block to be considered authentic.

   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 TBD. Temoprary used value

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INTERNET DRAFT         OSPF Link-local Signaling           November 2000

   is 2.

   The Length field in the header contains the length of the data
   portion of the TLV that includes 2 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 18.

   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 OSPF packet.

   The AuthData contains the message digest calculated for the LLS data

   The CA-TLV may appear in the LLS block only once. Also, when present,
   this TLV should be the last 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 the OSPF working
   group.  In the event that the OSPF working group has disbanded the
   review shall be performed by a recommended Designated Expert.

   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.

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.

5 Security considerations

   The described technique provides the same level of security as OSPF
   protocol by allowing LLS data to be authenticated (see Section 2.4.2
   for more details).

6 Acknowledgements

   The authors would like to acknowledge Russ White for his review of
   this document.

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INTERNET DRAFT         OSPF Link-local Signaling           November 2000

7 References

        J. Moy. OSPF version 2. Technical Report RFC 2328, Internet
        Engineering Task Force, 1998.  ftp://ftp.isi.edu/in-

   [IANA]T. Narten, H. Alvestrand. Guidelines for Writing an IANA Con-
        siderations Section in RFCs. Best current practice RFC 2434.

8 Authors' addresses

        Alex Zinin                        Barry Friedman
        Cisco Systems                     Cisco Systems
        150 W. Tasman Dr.                 170 W. Tasman Dr.
        San Jose,CA 95134                 San Jose,CA 95134
        USA                               USA
        E-mail: azinin@cisco.com          E-mail: friedman@cisco.com

        Liem Nguyen                       Abhay Roy
        7025 Kit Creek Rd.                Cisco Systems
        Research Triangle Park, NC 27709  170 W. Tasman Dr.
        USA                               San Jose,CA 95134
        e-mail: lhnguyen@cisco.com        USA
                                          E-mail: akr@cisco.com

        Derek M. Yeung
        Procket Networks
        3850 N.First Street
        San Jose, CA 95134
        Phone: 408-954-7911
        Fax:   408-987-6166
        Email: myeung@procket.com

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