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Versions: (RFC 2370) 00 draft-ietf-ospf-rfc2370bis

Internet Draft                                         Lou Berger (LabN)
Obsoletes: 2370                                      Igor Bryskin (Adva)
Category: Standards Track                           Alex Zinin (Alcatel)
Expiration Date: April 2007                             Original Author:
                                       Rob Coltun (Acoustra Productions)

                                                            October 2006


                       The OSPF Opaque LSA Option


                  draft-berger-ospf-rfc2370bis-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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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
   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.

   This document replaces [RFC2370], and adds to it a mechanism to
   enable an OSPF router to validate AS-scope opaque LSAs originated
   outside of the router's OSPF area.





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Contents

 1      Conventions used in this document  .........................   3
 2      Overview  ..................................................   3
 2.1    Organization Of This Document  .............................   3
 2.2    Acknowledgments  ...........................................   4
 3      The Opaque LSA  ............................................   4
 3.1    Flooding Opaque LSAs  ......................................   5
 3.2    Modifications To The Neighbor State Machine  ...............   6
 4      Protocol Data Structures  ..................................   7
 4.1    Additions To The OSPF Neighbor Structure  ..................   7
 5      Management Considerations  .................................   8
 6      Inter-Area Considerations  .................................  10
 7      Backward Compatibility  ....................................  11
 8      Security Considerations  ...................................  11
 9      IANA Considerations  .......................................  12
10      References  ................................................  13
10.1    Normative References  ......................................  13
10.2    Informative References  ....................................  13
11      Author's Addresses  ........................................  13
12      Appendix A: OSPF Data formats  .............................  14
12.1    The Options Field  .........................................  14
12.2    The Opaque LSA  ............................................  15
13      Full Copyright Statement  ..................................  17
14      Intellectual Property  .....................................  17

















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1. Conventions used in this document

   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 [RFC2119].


2. 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.  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.






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2.2. Acknowledgments

   We would like to thank Acee Lindem for his review and useful
   feedback.  The handling of AS-scope opaque LSAs described in this
   document is taken from draft-bryskin-ospf-lsa-
   type11-validation-00.txt.


3. 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. 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



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   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 typically 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;



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   the O-bit MUST NOT be set in packets other than Database Description
   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]) when 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 MUST placed on the link-state
   retransmission lists of opaque-capable neighbors, and MUST NOT be
   placed on the link-state retransmission lists of non-opaque-capable
   neighbors.  However, 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).

   Routers processing opaque LSAs MAY choose to give priority to
   processing base OSPF LSA types over opaque LSA 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 MUST be omitted from a virtual neighbor's Database
                summary list. AS External LSAs and type-11 Opaque LSAs
                MUST be omitted from the Database summary list if the
                area has been configured as a stub area (see Section 3.6
                of [OSPF]).



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                Type-9 Opaque LSAs MUST be 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).

                Any advertisement whose age is equal to MaxAge MUST be
                omitted from the Database summary list. It MUST instead
                be 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 MUST have a DD sequence
                number, and MUST be 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. 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



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       more detailed explanation of the flooding of the Opaque LSA see
       section 3 of this document.


5. 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.  NOTE: This
   section does not apply to routers supporting [MIB-UPDATE].

   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



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     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.

     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



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     for displaying the type-11 link-state database.  Entries in this
     table should be indexed with the Opaque type, link-state ID and the
     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. Inter-Area Considerations

   As defined above, link-state type 11 opaque LSAs are flooded
   throughout the Autonomous System (AS). One issue related to AS scoped
   Opaque LSAs is that there must be a way for OSPF routers in remote
   areas to check availability of the LSA originator.  Specifically, if
   an OSPF router originates a type-11 LSA and, after that, goes out of
   service, OSPF routers located outside of the originator's OSPF area
   have no way of detecting this fact and may use the stale information
   for a considerable period of time (up to 60 minutes). This could
   prove to be suboptimal for some applications, and may result in
   others not functioning.

   Type-9 opaque LSAs and type-10 opaque LSAs do not have this problem
   as a receiving router can detect an out of service router via the
   loss of an OSPF adjacency, in the case of type-9 LSAs, or the loss of
   the sequence of OSPF adjacencies, in the case of type-10 LSAs,
   connecting the LSA receiving and originating routers.

   There is a parallel issue in OSPF for the AS scoped AS-external-LSAs
   (type-5 LSAs).  OSPF addresses this by using AS border information
   advertised in ASBR-summary-LSAs (type-4 LSAs), see [OSPF] Section
   16.4. This same mechanism is reused by this document for type 11
   opaque LSAs.

   To enable OSPF routers in remote areas to check availability of the
   originator of link-state type 11 opaque LSAs, the originators
   advertise themselves as ASBRs. This will enable routers to track the
   reachability of the LSA originator either directly via the SPF
   calculation (for routers in the same area) or indirectly via type-4
   LSAs originated by ABRs (for routers in other areas). It is important
   to note that this solution MUST NOT be used in OSPF stub areas as
   neither type-11 LSAs are flooded nor type-4 LSAs are originated into
   such areas.

   The procedures related inter-area opaque LSAs are as follows:

   (1) An OSPF router that is configured to originate AS-scope opaque
       LSAs MUST set E-bit in the Options field of every originated
       OSPF Hello packet;




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   (2) Such routers also MUST set the E-bit in the Options field of the
       header of every LSA it injects into the network;

   (3) When processing a received type-11 Opaque LSA, the router MUST
       lookup the routing table entries (potentially one per attached
       area) for the AS boundary router (ASBR) that originated the LSA.
       If no entries exist for router ASBR (i.e., ASBR is unreachable),
       the router MUST do nothing with this LSA. It also MUST
       discontinue using all Opaque LSAs injected into the network by
       the same originator whenever it is detected that the originator
       is unreachable.


7. Backward Compatibility

   The solution proposed in this memo introduces no interoperability
   issues. In the case that a non-opaque-capable neighbor receives
   Opaque LSAs, per [OSPF], the non-opaque-capable router will simply
   discard the LSA.

   Note, that OSPF routers that implement [RFC2370] will continue using
   stale type-11 LSAs even when the LSA originator implements the Inter-
   area procedures, see Section 6, of this document.


8. 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.




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   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].

   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
   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.

   In the case of type-11 Opaque LSAs, this document reuses an ASBR
   tracking mechanism that is already employed in basic OSPF for type-5
   LSAs. Therefore, applying it to type-11 Opaque LSAs does not create
   any threats that are not already known for type-5 LSAs.


9. 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.



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10. References

10.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to indicate
             requirements levels", RFC 2119, March 1997.

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

   [IANA] Narten, T., and H. Alvestrand, "Guidelines for Writing an IANA
          Considerations Section in RFCs", BCP 26, October 1998.

   [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.


10.2. Informative References

   [RFC2370] Coltun, R., "The OSPF Opaque LSA Option", RFC 2370,
             July 1998.

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

   [MIB-UPDATE] Joyal, D., et. al., "OSPF Version 2 Management
                Information Base", draft-ietf-ospf-mib-update-, May
                2006.

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

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


11. Author's Addresses

   Lou Berger
   LabN Consulting, L.L.C.
   Email: lberger@labn.net









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   Igor Bryskin
   ADVA Optical Networking Inc
   7926 Jones Branch Drive
   Suite 615
   McLean, VA - 22102
   Email: ibryskin@advaoptical.com

   Alex Zinin
   Alcatel
   Email: zinin@psg.com

   Original Author:
   Rob Coltun
   Acoustra Productions


12. Appendix A: OSPF Data formats

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


12.1. 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



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   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].

   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.


12.2. 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



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   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 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 MUST NOT be flooded beyond the local
       (sub)network.

     o A value of 10 denotes an area-local scope. Opaque LSAs with a
       area-local scope MUST NOT be 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 MUST NOTE be 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 of this document for a description of Opaque type
   allocation and assignment.




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13. Full Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

   This document and the information contained herein are provided on an
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   ENGINEERING TASK FORCE DISCLAIM 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.


14. Intellectual Property

   The IETF takes no position regarding the validity or scope of any
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   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   The IETF invites any interested party to bring to its attention any
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