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Versions: (draft-coltun-ospf-opaque) 00 01 02 03 04 05 RFC 2370

Internet-Draft                    Opaque                           May 1997


Expiration Date: November 1997                                 FORE Systems
File name: draft-ietf-ospf-opaque-01.txt












                        The OSPF Opaque LSA Option






                                Rob Coltun
                               FORE Systems
                              (301) 571-2521
                             rcoltun@fore.com






     Status Of This Memo

     This document is an Internet-Draft.  Internet-Drafts are working docu-
     ments of the Internet Engineering Task Force (IETF), its areas, and
     its working groups.  Note that other groups may also distribute work-
     ing documents as Internet-Drafts.

     Internet-Drafts are draft documents valid for a maximum of six months
     and may be updated, replaced, or obsoleted by other documents at any
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     To learn the current status of any Internet-Draft, please check the
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     (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).




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     Table Of Contents

          1.0 Abstract ................................................. 3

          2.0 Overview ................................................. 3

          2.1 Organization Of This Document ............................ 3

          2.2 Acknowledgments .......................................... 4

          3.0 The Opaque LSA ........................................... 4

          3.1 Flooding Opaque LSAs ..................................... 5

          3.2 Modifications To The Neighbor State Machine .............. 6

          4.0 Protocol Data Structures ................................. 8

          4.1 Additions To The OSPF Neighbor Structure ................. 8

          5.0 References ............................................... 8

          Appendix A: OSPF Data Formats ................................ 10

          A.1 The Options Field ........................................ 10

          A.2 Opaque LSA ............................................... 12
























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     1.0  Abstract

     This memo documents enhancements to the OSPF protocol to support a new
     class of link-state advertisements (LSA) called Opaque LSAs.  The
     Opaque LSA option defines a general mechanism to allow for future
     extensibility of OSPF. The information contained in Opaque LSAs may be
     used directly by OSPF or by other protocols.  Opaque LSAs contain some
     number of octets padded to 32-bit alignment.  The standard OSPF link-
     state database flooding mechanisms are use for distribution of Opaque
     LSAs.  Opaque LSAs are flooded throughout all or some limited portion
     of the OSPF topology.

     2.0  Overview


     Over the last few years the OSPF routing protocol [OSPF] has been
     widely deployed throughout the Internet.  As a result of this deploy-
     ment and the evolution of networking technology, OSPF has been
     extended to support many options; this evolution will obviously con-
     tinue.

     This memo documents enhancements to the OSPF protocol to support a new
     class of link-state advertisements (LSA) called Opaque LSAs which
     defines an optional generalized mechanism to allow for future extensi-
     bility of OSPF. The information contained in Opaque LSAs may be used
     directly by OSPF or by other protocols.  For example, the OSPF LSA may
     be used to distribute BGP AS Path information (as documented in The
     OSPF External Attributes LSA [EAL]) which is then used by BGP route-
     leaking mechanisms. The option may also be used to distribute IP QoS
     information which may be used directly by an OSPF path computation.
     The exact use of Opaque LSAs is beyond the scope of this draft.

     The data contained in an Opaque LSA is some number of 32-bit aligned
     octets.  Like any other LSA, the Opaque LSA uses the link-state data-
     base distribution mechanism for flooding this information throughout
     the topology.  The link-state type of the Opaque LSA identifies the
     Flooding Scope or range of the topology to which this LSA may be dis-
     tributed to.


     2.1  Organization Of This Document

     This document first defines the three types of Opaque LSAs followed by
     a description of OSPF packet processing which includes modifications
     to the flooding procedure and the neighbor state machine needed to
     support the Opaque LSA.  Appendix A then gives the packet formats.





Coltun                                                             [Page 3]


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     2.2 Acknowledgments

     The author would like to thank Dennis Ferguson, Acee Lindem, John Moy,
     Sandra Murphy, Zhaohui "Jeffrey" Zhang and the rest of the OSPF Work-
     ing 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.  Each
     type has a unique flooding scope and may be originated by any router.
     The data contained in the Opaque LSA consists of some number of octets
     aligned to a 32-bit boundary.  Like any other LSA, Opaque LSAs use the
     link-state database distribution mechanism for flooding this informa-
     tion throughout the topology.  The Opaque LSA's link-state type iden-
     tifies the range of the topology to which this LSA may be distributed
     to.  This section documents the flooding of Opaque LSAs.

     The following are possible values of the link-state type filed with
     their related flooding scope.

          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 area that they are originated
          into.

          o Link-state type 11 denotes that the LSA is flooded throughout
          the Autonomous System (AS). Type 11 LSAs maintain the flooding
          scope of existing OSPF areas. 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 within 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.

     Origination of Opaque LSAs are unique to the application using it.
     The link-state ID of the Opaque LSA is divided into a type field (the
     first 8 bits) a type-specific ID (the remaining 24 bits).  The packet
     format of the Opaque LSA is given in Appendix A.

     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 (i.e., a type 11 (domain-wide) Opaque LSA is not



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     accepted in a stub area).  Flooding scope effects both the building of
     the Database summary list during the initial synchronization of the
     link-state database and the flooding procedure.

     In order to make the use of the Opaque LSAs predictable, it is recom-
     mended that all routers within the scope of use have the same Opaque
     LSA capabilities. For example, if the Opaque LSA is to be used for
     flooding Opaque information throughout a single area, all routers
     within the area should support the Opaque option.

     The following describes the modifications to these procedures that are
     necessary to insure proper use of 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. The flooding mechanisms must suppress the
     flooding of Opaque LSAs as described in the following.


          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 neighbor), the Opaque LSA must not be flooded out that
          interface (or to that neighbor).  An implementation should keep
          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 is not the area associ-
          ated with a particular 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 flooding scope is the entire
          AS) and 1) the area associated with Opaque LSA is not the area
          associated with a particular interface (i.e., the target area is
          not the same) and 2) the target area is a stub area, the Opaque
          LSA must not be flooded out the interface.

          o If an Opaque LSA is received on an interface associated with a
          stub area the LSA, the LSA is to be discarded and not ack-
          nowledged since neighboring router has flooded the LSA in error
          (see Section 13 of [OSPF], receiving LSAs having unknown LS
          types).




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     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.
     Then, in the next step of the Database Exchange process, Opaque LSAs
     are included in the Database summary list 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 Sec-
     tion 13.3 of [OSPF], Opaque LSAs are only placed on the link-state
     retransmission lists of opaque-capable neighbors.  Note however that
     when sending 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 the action is changed to the fol-
     lowing.

      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



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                 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 (see Section 3.6 of [OSPF]).

                 Opaque LSAs are omitted from the Database
                 summary list if the following conditions are met:
                 1) the LSA type is type 9 (the flooding scope
                 is link-local) and the interface associated with
                 the Opaque LSA (upon reception) does not equal the
                 interface associated with the neighbor;
                 2) the LSA type is 10 (the flooding scope is
                 area-local) and the area associated with Opaque
                 LSA is not the area associated with the neighbor's
                 interface.

                 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 10.8 and 10.6 of [OSPF].






















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     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 OSPF
     implementation. Besides the data structures listed below, this specif-
     ication will also reference 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 recep-
          tion of the neighbor's Database Description packets, and deter-
          mines whether Opaque LSAs are flooded to the neighbor. For a more
          detailed explanation of the flooding of the Opaque LSA see sec-
          tion 3 of this document.




     5.0 References



         [OSPF] Moy, J., "OSPF Version 2", IETF Internet Draft,
                Cascade, April 1997.

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

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



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

         [EAL] Ferguson, D., "The OSPF External Attributes LSA", work in
               progress.














































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     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 capa-
     bilities, 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.

     Seven 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 Pack-
     ets, Database Description packets or link-state advertisements should
     ignore the capability and process the packet/advertisement normally.



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

                              The Options Field


     T-bit
          This bit describes the router's TOS-based routing capability, as
          specified in Sections 9.5, 10.8, 12.1.2 and 16.9 of [OSPF].

     E-bit



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          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].

     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 for-
          ward External-Attributes-LSAs, as specified in [EAL].


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




























Coltun                                                            [Page 11]


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     A.2 Opaque LSA

     Opaque LSAs are the Type 9, 10 and 11 link-state advertisements. These
     advertisements are originated by any router and may be used directly
     by OSPF or indirectly by other protocols such as BGP wishing to dis-
     tribute information throughout the OSPF domain.  The primary function
     of the Opaque LSA is to provide for future extensibility to OSPF.

     The data contained in the Opaque LSA consists of some number of octets
     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).

     Origination of Opaque LSAs are unique to the application using it.
     Section 3 of this document describes the flooding procedures for the
     Opaque LSA.


        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 identifies the flooding scope (or range) of
          the topology to which this LSA may be distributed to. The follow-
          ing 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



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          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).  Opaque type values in the range of 128-255 are reserved
          for private and experimental use.

































Coltun                                                            [Page 13]


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