rfc2740.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   as tiebreakers (see Section 13.1 of [Ref1]).

   In IPv6, the link-state database is split across three separate data
   structures. LSAs with AS flooding scope are contained within the
   top-level OSPF data structure (see Section 3.1) as long as either
   their LS type is known or their U-bit is 1 (flood even when
   unrecognized); this includes the AS-external-LSAs. LSAs with area
   flooding scope are contained within the appropriate area structure
   (see Section 3.1.1) as long as either their LS type is known or their
   U-bit is 1 (flood even when unrecognized); this includes router-LSAs,
   network-LSAs, inter-area-prefix-LSAs, inter-area-router-LSAs, and
   intra-area-prefix-LSAs. LSAs with unknown LS type and U-bit set to 0
   and/or link-local flooding scope are contained within the appropriate
   interface structure (see Section 3.1.2); this includes link-LSAs.

   To lookup or install an LSA in the database, you first examine the LS
   type and the LSA's context (i.e., to which area or link does the LSA
   belong). This information allows you to find the correct list of
   LSAs, all of the same LS type, where you then search based on the
   LSA's Link State ID and Advertising Router.

3.4.3.  Originating LSAs

   The process of reoriginating an LSA in IPv6 is the same as in IPv4:
   the LSA's LS sequence number is incremented, its LS age is set to 0,
   its LS checksum is calculated, and the LSA is added to the link state
   database and flooded out the appropriate interfaces.

   To the list of events causing LSAs to be reoriginated, which for IPv4
   is given in Section 12.4 of [Ref1], the following events and/or
   actions are added for IPv6:

   o  The state of one of the router's interfaces changes. The router
      may need to (re)originate or flush its Link-LSA and one or more
      router-LSAs and/or intra-area-prefix-LSAs.

   o  The identity of a link's Designated Router changes. The router may
      need to (re)originate or flush the link's network-LSA and one or
      more router-LSAs and/or intra-area-prefix-LSAs.






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   o  A neighbor transitions to/from "Full" state.  The router may need
      to (re)originate or flush the link's network-LSA and one or more
      router-LSAs and/or intra-area-prefix-LSAs.

   o  The Interface ID of a neighbor changes. This may cause a new
      instance of a router-LSA to be originated for the associated area,
      and the reorigination of one or more intra-area-prefix-LSAs.

   o  A new prefix is added to an attached link, or a prefix is deleted
      (both through configuration). This causes the router to
      reoriginate its link-LSA for the link, or, if it is the only
      router attached to the link, causes the router to reoriginate an
      intra-area-prefix-LSA.

   o  A new link-LSA is received, causing the link's collection of
      prefixes to change. If the router is Designated Router for the
      link, it originates a new intra-area-prefix-LSA.

   Detailed construction of the seven required IPv6 LSA types is
   supplied by the following subsections. In order to display example
   LSAs, the network map in Figure 15 of [Ref1] has been reworked to
   show IPv6 addressing, resulting in Figure 1. The OSPF cost of each
   interface is has been displayed in Figure 1. The assignment of IPv6
   prefixes to network links is shown in Table 1. A single area address
   range has been configured for Area 1, so that outside of Area 1 all
   of its prefixes are covered by a single route to 5f00:0000:c001::/48.
   The OSPF interface IDs and the link-local addresses for the router
   interfaces in Figure 1 are given in Table 2.























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RFC 2740                     OSPF for IPv6                 December 1999


       ..........................................
       .                                  Area 1.
       .     +                                  .
       .     |                                  .
       .     | 3+---+1                          .
       .  N1 |--|RT1|-----+                     .
       .     |  +---+      \                    .
       .     |              \  ______           .
       .     +               \/       \      1+---+
       .                     *    N3   *------|RT4|------
       .     +               /\_______/       +---+
       .     |              /     |             .
       .     | 3+---+1     /      |             .
       .  N2 |--|RT2|-----+      1|             .
       .     |  +---+           +---+           .
       .     |                  |RT3|----------------
       .     +                  +---+           .
       .                          |2            .
       .                          |             .
       .                   +------------+       .
       .                          N4            .
       ..........................................

       Figure 1: Area 1 with IP addresses shown


              Network   IPv6 prefix
              -----------------------------------
              N1        5f00:0000:c001:0200::/56
              N2        5f00:0000:c001:0300::/56
              N3        5f00:0000:c001:0100::/56
              N4        5f00:0000:c001:0400::/56

       Table 1: IPv6 link prefixes for sample network


            Router   interface   Interface ID   link-local address
            -------------------------------------------------------
            RT1      to N1       1              fe80:0001::RT1
                     to N3       2              fe80:0002::RT1
            RT2      to N2       1              fe80:0001::RT2
                     to N3       2              fe80:0002::RT2
            RT3      to N3       1              fe80:0001::RT3
                     to N4       2              fe80:0002::RT3
            RT4      to N3       1              fe80:0001::RT4

       Table 2: OSPF Interface IDs and link-local addresses




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3.4.3.1.  Router-LSAs

   The LS type of a router-LSA is set to the value 0x2001.  Router-LSAs
   have area flooding scope. A router may originate one or more router-
   LSAs for a given area. Each router-LSA contains an integral number of
   interface descriptions; taken together, the collection of router-LSAs
   originated by the router for an area describes the collected states
   of all the router's interfaces to the area. When multiple router-LSAs
   are used, they are distinguished by their Link State ID fields.

   The Options field in the router-LSA should be coded as follows. The
   V6-bit should be set. The E-bit should be clear if and only if the
   attached area is an OSPF stub area. The MC-bit should be set if and
   only if the router is running MOSPF (see [Ref8]). The N-bit should be
   set if and only if the attached area is an OSPF NSSA area.  The R-bit
   should be set. The DC-bit should be set if and only if the router can
   correctly process the DoNotAge bit when it appears in the LS age
   field of LSAs (see [Ref11]). All unrecognized bits in the Options
   field should be cleared

   To the left of the Options field, the router capability bits V, E and
   B should be coded according to Section 12.4.1 of [Ref1]. Bit W should
   be coded according to [Ref8].

   Each of the router's interfaces to the area are then described by
   appending "link descriptions" to the router-LSA. Each link
   description is 16 bytes long, consisting of 5 fields: (link) Type,
   Metric, Interface ID, Neighbor Interface ID and Neighbor Router ID
   (see Section A.4.3). Interfaces in state "Down" or "Loopback" are not
   described (although looped back interfaces can contribute prefixes to
   Intra-Area-Prefix-LSAs). Nor are interfaces without any full
   adjacencies described. All other interfaces to the area add zero, one
   or more link descriptions, the number and content of which depend on
   the interface type. Within each link description, the Metric field is
   always set the interface's output cost and the Interface ID field is
   set to the interface's OSPF Interface ID.

   Point-to-point interfaces
      If the neighboring router is fully adjacent, add a Type 1 link
      description (point-to-point). The Neighbor Interface ID field is
      set to the Interface ID advertised by the neighbor in its Hello
      packets, and the Neighbor Router ID field is set to the neighbor's
      Router ID.








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RFC 2740                     OSPF for IPv6                 December 1999


   Broadcast and NBMA interfaces
      If the router is fully adjacent to the link's Designated Router,
      or if the router itself is Designated Router and is fully adjacent
      to at least one other router, add a single Type 2 link description
      (transit network). The Neighbor Interface ID field is set to the
      Interface ID advertised by the Designated Router in its Hello
      packets, and the Neighbor Router ID field is set to the Designated
      Router's Router ID.

   Virtual links
      If the neighboring router is fully adjacent, add a Type 4 link
      description (virtual). The Neighbor Interface ID field is set to
      the Interface ID advertised by the neighbor in its Hello packets,
      and the Neighbor Router ID field is set to the neighbor's Router
      ID. Note that the output cost of a virtual link is calculated
      during the routing table calculation (see Section 3.7).

   Point-to-MultiPoint interfaces
      For each fully adjacent neighbor associated with the interface,
      add a separate Type 1 link description (point-to-point) with
      Neighbor Interface ID field set to the Interface ID advertised by
      the neighbor in its Hello packets, and Neighbor Router ID field
      set to the neighbor's Router ID.

   As an example, consider the router-LSA that router RT3 would
   originate for Area 1 in Figure 1. Only a single interface must be
   described, namely that which connects to the transit network N3. It
   assumes that RT4 has been elected Designated Router of Network N3.

     ; RT3's router-LSA for Area 1

     LS age = 0                     ;newly (re)originated
     LS type = 0x2001               ;router-LSA
     Link State ID = 0              ;first fragment
     Advertising Router = 192.1.1.3 ;RT3's Router ID
     bit E = 0                      ;not an AS boundary router
     bit B = 1                      ;area border router
     Options = (V6-bit|E-bit|R-bit)
         Type = 2                     ;connects to N3
         Metric = 1            ;cost to N3
         Interface ID = 1             ;RT3's Interface ID on N3
         Neighbor Interface ID = 1    ;RT4's Interface ID on N3
         Neighbor Router ID = 192.1.1.4 ; RT4's Router ID

   If for example another router was added to Network N4, RT3 would have
   to advertise a second link description for its connection to (the now
   transit) network N4. This could be accomplished by reoriginating the
   above router-LSA, this time with two link descriptions. Or, a



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RFC 2740                     OSPF for IPv6                 December 1999


   separate router-LSA could be originated with a separate Link State ID
   (e.g., using a Link State ID of 1) to describe the connection to N4.

   Host routes no longer appear in the router-LSA, but are instead
   included in intra-area-prefix-LSAs.

3.4.3.2.  Network-LSAs

   The LS type of a network-LSA is set to the value 0x2002.  Network-
   LSAs have area flooding scope. A network-LSA is originated for every
   broadcast or NBMA link having two or more attached routers, by the
   link's Designated Router. The network-LSA lists all routers attached
   to the link.

   The procedure for originating network-LSAs in IPv6 is the same as the
   IPv4 procedure documented in Section 12.4.2 of [Ref1], with the
   following exceptions:

   o  An IPv6 network-LSA's Link State ID is set to the In