rfc1587.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

            the type-5 LSA is suppressed and the component networks
            remain hidden from the rest of the AS.

            By default (given that the P-bit is set and the LSA has a
            non-zero forwarding address) if a network is not contained
            in any explicitly configured address range, a type-7 to
            type-5 LSA translation will occur.

            A new instance of a type-5 LSA should be originated and
            flooded to all attached type-5 capable areas if one of the
            following is true.

            1. There currently is no type-5 LSA originated from this
               router corresponding to the type-7 LSA.

            2. The path type or the metric in the corresponding
               type-5 LSA is different from the type-7 LSA.

            3. The forwarding address in the corresponding
               type-5 LSA is different from the type-7 LSA.

            The newly originated type-5 LSAs will describe the same
            network and have the same network mask, metrics, forwarding
            address, external route tag and path type as the type-7 LSA.
            The advertising router field will be the router ID of this
            area border router.

            As with all newly originated type-5 LSAs, a type-5 LSA that
            is the result of a type-7 to type-5 translation (type-7 range
            or default case) is flooded to all attached type-5 capable
            areas.




Coltun & Fuller                                                [Page 12]

RFC 1587                    OSPF NSSA Option                  March 1994


4.2 Flushing Translated Type-7 LSAs

   If an NSSA area border router has translated a type-7 LSA to a type-5
   LSA that should no longer be translated, the type-5 LSA should be
   flushed (set to MaxAge and flooded).  The translated type-5 LSA
   should be flushed whenever the routing table entry that caused the
   translation changes so that either the routing table entry is
   unreachable or the entry's associated LSA is not a type-7 with the
   P-bit set and a non-zero forwarding address.

5.0 Acknowledgements

   This document was produced by the OSPF Working Group, chaired by John
   Moy.

   In addition, the comments of the following individuals are also
   acknowledged:

                  Phani Jajjarvarpu  cisco
                  Dino Farinacci     cisco
                  Jeff Honig         Cornell University
                  John Moy           Proteon, Inc.
                  Doug Williams      IBM

6.0 References

   [1] Moy, J., "OSPF Version 2", RFC 1583, Proteon, Inc., March 1994.

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

7.0 Security Considerations

   Security issues are not discussed in this memo.

















Coltun & Fuller                                                [Page 13]

RFC 1587                    OSPF NSSA Option                  March 1994


8.0 Authors' Addresses

   Rob Coltun
   RainbowBridge Communications

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


   Vince Fuller
   BARRNet
   Stanford University
   Pine Hall 115
   Stanford, CA, 94305-4122

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


































Coltun & Fuller                                                [Page 14]

RFC 1587                    OSPF NSSA Option                  March 1994


Appendix A: Type-7 Packet Format

          0                                32
          -----------------------------------
          |                | OPTS   |   7   |
          |                ------------------
          |        Link-State Header        |
          |                                 |
          -----------------------------------
          | Network Mask                    |
          -----------------------------------  ______
          |E| Tos  |        metric          |  .
          -----------------------------------  .  repeated for each TOS
          | Forwarding Address              |  .
          -----------------------------------  .
          | External Route Tag              |  ______
          -----------------------------------

   The definitions of the link-state ID, network mask, metrics and
   external route tag are the same as the definitions for the type-5
   LSAs (see A.4.5 in the OSPF specification) except for:

               The Forwarding Address

   If the network between the NSSA AS boundary router and the adjacent
   AS is advertised into OSPF as an internal OSPF route, the forwarding
   address should be the next hop address but if the intervening network
   is not advertised into OSPF as an internal OSPF route, the forwarding
   address should be any one of the router's active OSPF interface
   addresses.





















Coltun & Fuller                                                [Page 15]

RFC 1587                    OSPF NSSA Option                  March 1994


Appendix B: The Options Field

   The OSPF options field is present in OSPF Hello packets, Database
   Description packets and all link-state advertisements. See appendix
   A.2 in the OSPF specification for a description of option field.

                   ------------------------------------
                   | * | * | * | * | N/P | MC | E | T |
                   ------------------------------------

                       The Type-7 LSA options field


             T-bit:  The T-bit describes the router's TOS capability.

             E-bit:  Type-5 AS external link advertisements are not
                     flooded into/through OSPF stub and NSSA areas.
                     The E-bit ensures that all members of a stub area
                     agree on that area configuration. The E-bit is
                     meaningful only in OSPF Hello packets. When the
                     E-bit is reset in the Hello packet sent out a
                     particular interface, it means that the router
                     will neither send nor receive type-5 AS external
                     link state advertisements on that interface (in
                     other words, the interface connects to a stub
                     area). Two routers will not become neighbors
                     unless they agree on the state of the E-bit.

             MC-bit: The MC-bit describes the multicast capability of
                     the various pieces of the OSPF routing domain
                     [2].

             N-bit:  The N-bit describes the the router's NSSA
                     capability.  The N-bit is used only in Hello
                     packets and ensures that all members of an NSSA
                     agree on that area's configuration. When the
                     N-bit is reset in the Hello packet sent out a
                     particular interface, it means that the router
                     will neither send nor receive type-7 LSAs on that
                     interface. Two routers will not form an adjacency
                     unless they agree on the state of the N-bit. If
                     the N-bit is set in the options field, the E-bit
                     must be reset.

             P-bit:  The P-bit is used only in the type-7 LSA header.
                     It flags the NSSA area border router to translate
                     the type-7 LSA into a type-5 LSA.




Coltun & Fuller                                                [Page 16]

RFC 1587                    OSPF NSSA Option                  March 1994


Appendix C:  Configuration Parameters

   Appendix C.2 in the OSPF specification lists the area parameters.
   The area ID, list of address ranges for type-3 summary routes and
   authentication type remain unchanged.  Section 3.2 of this document
   lists the configuration parameters for type-7 address ranges.

   For NSSAs the external capabilities of the area must be set to accept
   type-7 external routes.  Additionally there must be a way of
   configuring the NSSA area border router to send a default route into
   the NSSA using a specific metric (type-1 or type-2 and the actual
   cost).







































Coltun & Fuller                                                [Page 17]