rfc2370.txt

RFC 的详细文档！

   [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: [phone]
   EMail: [e-mail]

































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]