Network Working Group                                          R. Coltun
Request for Comments: 2370                                  FORE Systems
See Also: 2328                                                 July 1998
Category: Standards Track


                       The OSPF Opaque LSA Option

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) The Internet Society (1998).  All Rights Reserved.

Table Of Contents

   1.0 Abstract .................................................  1
   2.0 Overview .................................................  2
   2.1 Organization Of This Document ............................  2
   2.2 Acknowledgments ..........................................  3
   3.0 The Opaque LSA ...........................................  3
   3.1 Flooding Opaque LSAs .....................................  4
   3.2 Modifications To The Neighbor State Machine ..............  5
   4.0 Protocol Data Structures .................................  6
   4.1 Additions To The OSPF Neighbor Structure .................  6
   5.0 Management Considerations ................................  7
   6.0 Security Considerations ..................................  9
   7.0 IANA Considerations ...................................... 10
   8.0 References ............................................... 10
   9.0 Author's Information ..................................... 11
   Appendix A: OSPF Data Formats ................................ 12
   A.1 The Options Field ........................................ 12
   A.2 The Opaque LSA ........................................... 13
   Appendix B: Full Copyright Statment .......................... 15

1.0  Abstract

   This memo defines enhancements to the OSPF protocol to support a new
   class of link-state advertisements (LSA) called Opaque LSAs.  Opaque
   LSAs provide a generalized mechanism to allow for the future
   extensibility of OSPF. Opaque LSAs consist of a standard LSA header
   followed by application-specific information.  The information field



Coltun                      Standards Track                     [Page 1]

RFC 2370               The OSPF Opaque LSA Option              July 1998


   may be used directly by OSPF or by other applications.  Standard OSPF
   link-state database flooding mechanisms are used to distribute Opaque
   LSAs to all or some limited portion of the OSPF topology.

2.0  Overview

   Over the last several years the OSPF routing protocol [OSPF] has been
   widely deployed throughout the Internet.  As a result of this
   deployment and the evolution of networking technology, OSPF has been
   extended to support many options; this evolution will obviously
   continue.

   This memo defines enhancements to the OSPF protocol to support a new
   class of link-state advertisements (LSA) called Opaque LSAs.  Opaque
   LSAs provide a generalized mechanism to allow for the future
   extensibility of OSPF. The information contained in Opaque LSAs may
   be used directly by OSPF or indirectly by some application wishing to
   distribute information throughout the OSPF domain.  For example, the
   OSPF LSA may be used by routers to distribute IP to link-layer
   address resolution information (see [ARA] for more information).  The
   exact use of Opaque LSAs is beyond the scope of this memo.

   Opaque LSAs consist of a standard LSA header followed by a 32-bit
   qaligned application-specific information field.  Like any other LSA,
   the Opaque LSA uses the link-state database distribution mechanism
   for flooding this information throughout the topology.  The link-
   state type field of the Opaque LSA identifies the LSA's range of
   topological distribution. This range is referred to as the Flooding
   Scope.

   It is envisioned that an implementation of the Opaque option provides
   an application interface for 1) encapsulating application-specific
   information in a specific Opaque type, 2) sending and receiving
   application-specific information, and 3) if required, informing the
   application of the change in validity of previously received
   information when topological changes are detected.

2.1  Organization Of This Document

   This document first defines the three types of Opaque LSAs followed
   by a description of OSPF packet processing. The packet processing
   sections include modifications to the flooding procedure and to the
   neighbor state machine. Appendix A then gives the packet formats.








Coltun                      Standards Track                     [Page 2]

RFC 2370               The OSPF Opaque LSA Option              July 1998


2.2 Acknowledgments

   The author would like to thank Dennis Ferguson, Acee Lindem, John
   Moy, Sandra Murphy, Man-Kit Yeung, Zhaohui "Jeffrey" Zhang and the
   rest of the OSPF Working Group for the ideas and support they have
   given to this project.

3.0 The Opaque LSA

   Opaque LSAs are types 9, 10 and 11 link-state advertisements.  Opaque
   LSAs consist of a standard LSA header followed by a 32-bit aligned
   application-specific information field.  Standard link-state database
   flooding mechanisms are used for distribution of Opaque LSAs.  The
   range of topological distribution (i.e., the flooding scope) of an
   Opaque LSA is identified by its link-state type.  This section
   documents the flooding of Opaque LSAs.

   The flooding scope associated with each Opaque link-state type is
   defined as follows.

     o Link-state type 9 denotes a link-local scope. Type-9 Opaque
       LSAs are not flooded beyond the local (sub)network.

     o Link-state type 10 denotes an area-local scope. Type-10 Opaque
       LSAs are not flooded beyond the borders of their associated area.

     o Link-state type 11 denotes that the LSA is flooded throughout
       the Autonomous System (AS). The flooding scope of type-11
       LSAs are equivalent to the flooding scope of AS-external (type-5)
       LSAs.  Specifically type-11 Opaque LSAs are 1) flooded throughout
       all transit areas, 2) not flooded into stub areas from the
       backbone and 3) not originated by routers into their connected
       stub areas.  As with type-5 LSAs, if a type-11 Opaque LSA is
       received in a stub area from a neighboring router within the
       stub area the LSA is rejected.

   The link-state ID of the Opaque LSA is divided into an Opaque type
   field (the first 8 bits) and a type-specific ID (the remaining 24
   bits).  The packet format of the Opaque LSA is given in Appendix A.
   Section 7.0 describes Opaque type allocation and assignment.

   The responsibility for proper handling of the Opaque LSA's flooding
   scope is placed on both the sender and receiver of the LSA.  The
   receiver must always store a valid received Opaque LSA in its link-
   state database.  The receiver must not accept Opaque LSAs that
   violate the flooding scope (e.g., a type-11 (domain-wide) Opaque LSA
   is not accepted in a stub area).  The flooding scope effects both the




Coltun                      Standards Track                     [Page 3]

RFC 2370               The OSPF Opaque LSA Option              July 1998


   synchronization of the link-state database and the flooding
   procedure.

   The following describes the modifications to these procedures that
   are necessary to insure conformance to the Opaque LSA's Scoping
   Rules.

3.1  Flooding Opaque LSAs

   The flooding of Opaque LSAs must follow the rules of Flooding Scope
   as specified in this section.  Section 13 of [OSPF] describes the
   OSPF flooding procedure.  The following describes the Opaque LSA's
   type-specific flooding restrictions.

     o If the Opaque LSA is type 9 (the flooding scope is link-local)
       and the interface that the LSA was received on is not the same as
       the target interface (e.g., the interface associated with a
       particular target neighbor), the Opaque LSA must not be flooded
       out that interface (or to that neighbor).  An implementation
       should keepk track of the IP interface associated with each
       Opaque LSA having a link-local flooding scope.

     o If the Opaque LSA is type 10 (the flooding scope is area-local)
       and the area associated with Opaque LSA (upon reception) is not
       the same as the area associated with the target interface, the
       Opaque LSA must not be flooded out the interface.  An
       implementation should keep track of the OSPF area associated
       with each Opaque LSA having an area-local flooding scope.

     o If the Opaque LSA is type 11 (the LSA is flooded throughout the
       AS) and the target interface is associated with a stub area the
       Opaque LSA must not be flooded out the interface.  A type-11
       Opaque LSA that is received on an interface associated with a
       stub area must be discarded and not acknowledged (the
       neighboring router has flooded the LSA in error).

   When opaque-capable routers and non-opaque-capable OSPF routers are
   mixed together in a routing domain, the Opaque LSAs are not flooded
   to the non-opaque-capable routers. As a general design principle,
   optional OSPF advertisements are only flooded to those routers that
   understand them.

   An opaque-capable router learns of its neighbor's opaque capability
   at the beginning of the "Database Exchange Process" (see Section 10.6
   of [OSPF], receiving Database Description packets from a neighbor in
   state ExStart). A neighbor is opaque-capable if and only if it sets
   the O-bit in the Options field of its Database Description packets;
   the O-bit is not set in packets other than Database Description



Coltun                      Standards Track                     [Page 4]

RFC 2370               The OSPF Opaque LSA Option              July 1998


   packets.  Then, in the next step of the Database Exchange process,
   Opaque LSAs are included in the Database summary list that is sent to
   the neighbor (see Sections 3.2 below and 10.3 of [OSPF]) if and only
   if the neighbor is opaque capable.

   When flooding Opaque-LSAs to adjacent neighbors, a opaque-capable
   router looks at the neighbor's opaque capability.  Opaque LSAs are
   only flooded to opaque-capable neighbors. To be more precise, in
   Section 13.3 of [OSPF], Opaque LSAs are only placed on the link-state
   retransmission lists of opaque-capable neighbors.  However, when send
   ing Link State Update packets as multicasts, a non-opaque-capable
   neighbor may (inadvertently) receive Opaque LSAs. The non-opaque-
   capable router will then simply discard the LSA (see Section 13 of
   [OSPF], receiving LSAs having unknown LS types).

3.2 Modifications To The Neighbor State Machine

   The state machine as it exists in section 10.3 of [OSPF] remains
   unchanged except for the action associated with State: ExStart,
   Event: NegotiationDone which is where the Database summary list is
   built.  To incorporate the Opaque LSA in OSPF this action is changed
   to the following.

     State(s):  ExStart

       Event:  NegotiationDone

     New state:  Exchange

       Action:  The router must list the contents of its entire area
                link-state database in the neighbor Database summary
                list.  The area link-state database consists of the
                Router LSAs, Network LSAs, Summary LSAs and types 9 and
                10 Opaque LSAs contained in the area structure, along
                with AS External and type-11 Opaque LSAs contained in
                the global structure. AS External and type-11 Opaque
                LSAs are omitted from a virtual neighbor's Database
                summary list. AS External LSAs and type-11 Opaque LSAs
                are omitted from the Database summary list if the area
                has been configured as a stub area (see Section 3.6 of
                [OSPF]).

                Type-9 Opaque LSAs are omitted from the Database summary
                list if the interface associated with the neighbor is
                not the interface associated with the Opaque LSA (as
                noted upon reception).





Coltun                      Standards Track                     [Page 5]

RFC 2370               The OSPF Opaque LSA Option              July 1998


                Any advertisement whose age is equal to MaxAge is
                omitted from the Database summary list. It is instead
                added to the neighbor's link-state retransmission list.
                A summary of the Database summary list will be sent to
                the neighbor in Database Description packets.  Each
                Database Description Packet has a DD sequence number,
                and is explicitly acknowledged.  Only one Database
                Description Packet is allowed to be outstanding at any
                one time. For more detail on the sending and receiving
                of Database Description packets, see Sections 10.6 and
                10.8 of [OSPF].

4.0  Protocol Data Structures

   The Opaque option is described herein in terms of its operation on
   various protocol data structures. These data structures are included
   for explanatory uses only, and are not intended to constrain an
   implementation. In addition to the data structures listed below, this
   specification references the various data structures (e.g., OSPF
   neighbors) defined in [OSPF].

   In an OSPF router, the following item is added to the list of global
   OSPF data structures described in Section 5 of [OSPF]:

     o Opaque capability. Indicates whether the router is running the
       Opaque option (i.e., capable of storing Opaque LSAs).  Such a
       router will continue to inter-operate with non-opaque-capable
       OSPF routers.

4.1 Additions To The OSPF Neighbor Structure

   The OSPF neighbor structure is defined in Section 10 of [OSPF].  In
   an opaque-capable router, the following items are added to the OSPF
   neighbor structure:

     o Neighbor Options. This field was already defined in the OSPF
       specification. However, in opaque-capable routers there is a new
       option which indicates the neighbor's Opaque capability. This new
       option is learned in the Database Exchange process through
       reception of the neighbor's Database Description packets, and
       determines whether Opaque LSAs are flooded to the neighbor. For a
       more detailed explanation of the flooding of the Opaque LSA see
       section 3 of this document.








Coltun                      Standards Track                     [Page 6]

RFC 2370               The OSPF Opaque LSA Option              July 1998


5.0 Management Considerations

   This section identifies the current OSPF MIB [OSPFMIB] capabilities
   that are applicable to the Opaque option and lists the additional
   management information which is required for its support.

   Opaque LSAs are types 9, 10 and 11 link-state advertisements.  The
   link-state ID of the Opaque LSA is divided into an Opaque type field
   (the first 8 bits) and a type-specific ID (the remaining 24 bits).
   The packet format of the Opaque LSA is given in Appendix A.  The
   range of topological distribution (i.e., the flooding scope) of an
   Opaque LSA is identified by its link-state type.

     o Link-State type 9 Opaque LSAs have a link-local scope. Type-9
       Opaque LSAs are flooded on a single local (sub)network but are
       not flooded beyond the local (sub)network.

     o Link-state type 10 Opaque LSAs have an area-local scope. Type-10
       Opaque LSAs are flooded throughout a single area but are not
       flooded beyond the borders of the associated area.

     o Link-state type 11 Opaque LSAs have an Autonomous-System-wide
       scope.  The flooding scope of type-11 LSAs are equivalent to the
       flooding scope of AS-external (type-5) LSAs.

   The OSPF MIB provides a number of objects that can be used to manage
   and monitor an OSPF router's Link-State Database.  The ones that are
   relevant to the Opaque option are as follows.

     The ospfGeneralGroup defines two objects for keeping track of newly
     originated and newly received LSAs (ospfOriginateNewLsas and
     ospfRxNewLsas respectively).

     The OSPF MIB defines a set of optional traps.  The ospfOriginateLsa
     trap signifies that a new LSA has been originated by a router and
     the ospfMaxAgeLsa trap signifies that one of the LSAs in the
     router's link-state database has aged to MaxAge.

     The ospfAreaTable describes the configured parameters and
     cumulative statistics of the router's attached areas. This table
     includes a count of the number of LSAs contained in the area's
     link-state database (ospfAreaLsaCount), and a sum of the LSA's LS
     checksums contained in this area (ospfAreaLsaCksumSum).  This sum
     can be used to determine if there has been a change in a router's
     link-state database, and to compare the link-state database of two
     routers.





Coltun                      Standards Track                     [Page 7]

RFC 2370               The OSPF Opaque LSA Option              July 1998


     The ospfLsdbTable describes the OSPF Process's link-state database
     (excluding AS-external LSAs).  Entries in this table are indexed
     with an Area ID, a link-state type, a link-state ID and the
     originating router's Router ID.

   The management objects that are needed to support the Opaque option
   are as follows.

     An Opaque-option-enabled object is needed to indicate if the Opaque
     option is enabled on the router.

     The origination and reception of new Opaque LSAs should be
     reflected in the counters ospfOriginateNewLsas and ospfRxNewLsas
     (inclusive for types 9, 10 and 11 Opaque LSAs).

     If the OSPF trap option is supported, the origination of new Opaque
     LSAs and purging of MaxAge Opaque LSAs should be reflected in the
     ospfOriginateLsa and ospfMaxAgeLsa traps (inclusive for types 9, 10
     and 11 Opaque LSAs).

     The number of type-10 Opaque LSAs should be reflected in
     ospfAreaLsaCount; the checksums of type-10 Opaque LSAs should be
     included in ospfAreaLsaChksumSum.

     Type-10 Opaque LSAs should be included in the ospfLsdbTable.  Note
     that this table does not include a method of examining the Opaque
     type field (in the Opaque option this is a sub-field of the link-
     state ID).

     Up until now, LSAs have not had a link-local scope so there is no
     method of requesting the number of, or examining the LSAs that are
     associated with a specific OSPF interface. A new group of
     management objects are required to support type-9 Opaque LSAs.
     These objects should include a count of type-9 Opaque LSAs, a
     checksum sum and a table for displaying the link-state database for
     type-9 Opaque LSAs on a per-interface basis.  Entries in this table
     should be indexed with an Area ID, interface's IP address, Opaque
     type, link-state ID and the originating router's Router ID.

     Prior to the introduction of type-11 Opaque LSAs, AS-External
     (type-5) LSAs have been the only link-state types which have an
     Autonomous-System-wide scope.  A new group of objects are required
     to support type-11 Opaque LSAs.  These objects should include a
     count of type-11 Opaque LSAs, a type-11 checksum sum and a table
     for displaying the type-11 link-state database.  Entries in this
     table should be indexed with the Opaque type, link-state ID and the





Coltun                      Standards Track                     [Page 8]

RFC 2370               The OSPF Opaque LSA Option              July 1998


     originating router's Router ID.  The type-11 link-state database
     table will allow type-11 LSAs to be displayed once for the router
     rather than once in each non-stub area.

6.0 Security Considerations

   There are two types of issues that need be addressed when looking at
   protecting routing protocols from misconfigurations and malicious
   attacks.  The first is authentication and certification of routing
   protocol information.  The second is denial of service attacks
   resulting from repetitive origination of the same router
   advertisement or origination a large number of distinct
   advertisements resulting in database overflow.  Note that both of
   these concerns exist independently of a router's support for the
   Opaque option.

   To address the authentication concerns, OSPF protocol exchanges are
   authenticated.  OSPF supports multiple types of authentication; the
   type of authentication in use can be configured on a per network
   segment basis. One of OSPF's authentication types, namely the
   Cryptographic authentication option, is believed to be secure against
   passive attacks and provide significant protection against active
   attacks. When using the Cryptographic authentication option, each
   router appends a "message digest" to its transmitted OSPF packets.
   Receivers then use the shared secret key and received digest to
   verify that each received OSPF packet is authentic.

   The quality of the security provided by the Cryptographic
   authentication option depends completely on the strength of the
   message digest algorithm (MD5 is currently the only message digest
   algorithm specified), the strength of the key being used, and the
   correct implementation of the security mechanism in all communicating
   OSPF implementations. It also requires that all parties maintain the
   secrecy of the shared secret key.  None of the standard OSPF
   authentication types provide confidentiality. Nor do they protect
   against traffic analysis.  For more information on the standard OSPF
   security mechanisms, see Sections 8.1, 8.2, and Appendix D of [OSPF].

   [DIGI] describes the extensions to OSPF required to add digital
   signature authentication to Link State data and to provide a
   certification mechanism for router data.  [DIGI] also describes the
   added LSA processing and key management as well as a method for
   migration from, or co-existence with, standard OSPF V2.

   Repetitive origination of advertisements are addressed by OSPF by
   mandating a limit on the frequency that new instances of any
   particular LSA can be originated and accepted during the flooding
   procedure.  The frequency at which new LSA instances may be



Coltun                      Standards Track                     [Page 9]

RFC 2370               The OSPF Opaque LSA Option              July 1998


   originated is set equal to once every MinLSInterval seconds, whose
   value is 5 seconds (see Section 12.4 of [OSPF]).  The frequency at
   which new LSA instances are accepted during flooding is once every
   MinLSArrival seconds, whose value is set to 1 (see Section 13,
   Appendix B and G.5 of [OSPF]).

   Proper operation of the OSPF protocol requires that all OSPF routers
   maintain an identical copy of the OSPF link-state database.  However,
   when the size of the link-state database becomes very large, some
   routers may be unable to keep the entire database due to resource
   shortages; we term this "database overflow".  When database overflow
   is anticipated, the routers with limited resources can be
   accommodated by configuring OSPF stub areas and NSSAs.  [OVERFLOW]
   details a way of gracefully handling unanticipated database
   overflows.

7.0 IANA Considerations

   Opaque types are maintained by the IANA.  Extensions to OSPF which
   require a new Opaque 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], Opaque type values in the
   range of 0-127 are allocated through an IETF Consensus action and
   Opaque type values in the range of 128-255 are reserved for private
   and experimental use.

8.0 References

   [ARA] Coltun, R., and J. Heinanen, "The OSPF Address Resolution
         Advertisement Option", Work in Progress.

   [DEMD] Moy, J., "Extending OSPF to Support Demand Circuits", RFC
          1793, April 1995.

   [DIGI] Murphy, S., Badger, M., and B. Wellington, "OSPF with Digital
          Signatures", RFC 2154, June 1997.

   [IANA] Narten, T., and H. Alvestrand, "Guidelines for Writing an IANA
          Considerations Section in RFCs", Work in Progress.

   [MOSPF] Moy, J., "Multicast Extensions to OSPF", RFC 1584, March
           1994.







Coltun                      Standards Track                    [Page 10]

RFC 2370               The OSPF Opaque LSA Option              July 1998


   [NSSA] Coltun, R., and V. Fuller, "The OSPF NSSA Option", RFC 1587,
          March 1994.

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

   [OSPFMIB] Baker, F., and R. Coltun, "OSPF Version 2 Management
             Information Base", RFC 1850, November 1995.

   [OVERFLOW] Moy, J., "OSPF Database Overflow", RFC 1765,
              March 1995.

9.0 Author's Information

   Rob Coltun
   FORE Systems

   Phone: (703) 245-4543
   EMail: rcoltun@fore.com

































Coltun                      Standards Track                    [Page 11]

RFC 2370               The OSPF Opaque LSA Option              July 1998


Appendix A: OSPF Data formats

   This appendix describes the format of the Options Field followed by
   the packet format of the Opaque LSA.

A.1 The Options Field

   The OSPF Options field is present in OSPF Hello packets, Database
   Description packets and all link-state advertisements.  The Options
   field enables OSPF routers to support (or not support) optional
   capabilities, and to communicate their capability level to other OSPF
   routers. Through this mechanism routers of differing capabilities can
   be mixed within an OSPF routing domain.

   When used in Hello packets, the Options field allows a router to
   reject a neighbor because of a capability mismatch.  Alternatively,
   when capabilities are exchanged in Database Description packets a
   router can choose not to forward certain link-state advertisements to
   a neighbor because of its reduced functionality.  Lastly, listing
   capabilities in link-state advertisements allows routers to forward
   traffic around reduced functionality routers by excluding them from
   parts of the routing table calculation.

   Six bits of the OSPF Options field have been assigned, although only
   the O-bit is described completely by this memo.  Each bit is
   described briefly below. Routers should reset (i.e., clear)
   unrecognized bits in the Options field when sending Hello packets or
   Database Description packets and when originating link-state
   advertisements. Conversely, routers encountering unrecognized Option
   bits in received Hello Packets, Database Description packets or
   link-state advertisements should ignore the capability and process
   the packet/advertisement normally.


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

                             The Options Field

   E-bit
        This bit describes the way AS-external-LSAs are flooded, as
        described in Sections 3.6, 9.5, 10.8 and 12.1.2 of [OSPF].

   MC-bit
        This bit describes whether IP multicast datagrams are forwarded
        according to the specifications in [MOSPF].




Coltun                      Standards Track                    [Page 12]

RFC 2370               The OSPF Opaque LSA Option              July 1998


   N/P-bit
        This bit describes the handling of Type-7 LSAs, as specified in
        [NSSA].

   DC-bit
        This bit describes the router's handling of demand circuits, as
        specified in [DEMD].

   EA-bit
        This bit describes the router's willingness to receive and
        forward External-Attributes-LSAs, as specified in [EAL].


   O-bit
        This bit describes the router's willingness to receive and
        forward Opaque-LSAs as specified in this document.

A.2 The Opaque LSA

   Opaque LSAs are Type 9, 10 and 11 link-state advertisements.  These
   advertisements may be used directly by OSPF or indirectly by some
   application wishing to distribute information throughout the OSPF
   domain.  The function of the Opaque LSA option is to provide for
   future extensibility of OSPF.

   Opaque LSAs contain some number of octets (of application-specific
   data) padded to 32-bit alignment.  Like any other LSA, the Opaque LSA
   uses the link-state database distribution mechanism for flooding this
   information throughout the topology.  However, the Opaque LSA has a
   flooding scope associated with it so that the scope of flooding may
   be link-local (type 9), area-local (type 10) or the entire OSPF
   routing domain (type 11).  Section 3 of this document describes the
   flooding procedures for the Opaque LSA.


















Coltun                      Standards Track                    [Page 13]

RFC 2370               The OSPF Opaque LSA Option              July 1998


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            LS age             |     Options   |   9, 10 or 11 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Opaque Type  |               Opaque ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Advertising Router                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      LS Sequence Number                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         LS checksum           |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                      Opaque Information                       |
      +                                                               +
      |                              ...                              |


   Link-State Type

     The link-state type of the Opaque LSA identifies the LSA's range of
     topological distribution. This range is referred to as the Flooding
     Scope.  The following explains the flooding scope of each of the
     link-state types.

     o A value of 9 denotes a link-local scope. Opaque LSAs with a
     link-local scope are not flooded beyond the local (sub)network.


     o A value of 10 denotes an area-local scope. Opaque LSAs with a
     area-local scope are not flooded beyond the area that they are
     originated into.

     o A value of 11 denotes that the LSA is flooded throughout the
     Autonomous System (e.g., has the same scope as type-5 LSAs).
     Opaque LSAs with AS-wide scope are not flooded into stub areas.

   Syntax Of The Opaque LSA's Link-State ID

   The link-state ID of the Opaque LSA is divided into an Opaque Type
   field (the first 8 bits) and an Opaque ID (the remaining 24 bits).
   See section 7.0 of this document for a description of Opaque type
   allocation and assignment.






Coltun                      Standards Track                    [Page 14]

RFC 2370               The OSPF Opaque LSA Option              July 1998


Appendix B.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























Coltun                      Standards Track                    [Page 15]