rfc2362.txt

RFC 的详细文档！

           5 The incoming interface is set to the interface used to
             send unicast packets to the RP in the (*,G) route entry,
             i.e., RPF interface toward the RP.

      2 For each address, Sj, in the join list whose RPT-bit and
        WC-bit are not set, and for which there is no existing (Sj,G)
        route entry, the router initiates one.  The router creates a
        (S,G) entry and copies all outgoing interfaces from the
        (S,G)RPT-bit entry, if it exists. If there is no (S,G) entry,
        the oif list is copied from the (*,G) entry; and if there is no
        (*,G) entry, the oif list is copied from the (*,*,RP) entry, if
        it exists. In all cases, the iif of the (S,G) entry is always
        excluded from the oif list.

           1 The outgoing interface for (Sj,G) is set to I.  The
             incoming interface for (Sj,G) is set to the interface used
             to send unicast packets to Sj (i.e., the RPF neighbor).

           2 If the interface used to reach Sj, is the same as I,
             this represents an error (or a unicast routing change) and
             the Join/Prune must not be processed.




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      3 For each address, Sj, in the join list of the Join/Prune
        message, for which there is an existing (Sj,G) route entry,

           1 If the RPT-bit is not set for Sj listed in the
             Join/Prune message, but the RPT-bit flag is set on the
             existing (Sj,G) entry, the router clears the RPT-bit flag
             on the (Sj,G) entry, sets the incoming interface to point
             towards Sj for that (Sj,G) entry, and sends a Join/Prune
             message corresponding to that entry through the new
             incoming interface; and

           2 If I is not the same as the existing incoming
             interface, the router adds I to the list of outgoing
             interfaces.

           3 The Oif-timer for I is increased (never decreased) to
             the Holdtime included in the Join/Prune message. In
             addition, if the Oif-timer for that interface is increased,
             the Oif-Deletion-Delay for that interface is set to 1/3rd
             the Holdtime specified in the Join/Prune message.

           4 The (Sj,G) entry's SPT bit is cleared until data comes
             down the shortest path tree.

      For each group address G, in the Join/Prune message, the
      associated prune list is processed as follows. We refer to each
      address in the prune list as Sp; Sp refers to the RP if the RPT-
      bit and WC-bit are both set. For each Sp in the prune list of the
      Join/Prune message:

      1 For each address, Sp, in the prune list whose RPT-bit and
        WC-bit are cleared:

           1 If there is an existing (Sp,G) route entry, the router
             lowers the entry's Oif-timer for I to its Oif-Deletion-
             Delay, allowing for other downstream routers on a multi-
             access LAN to override the prune. However, on point-to-
             point links, the oif-timer is expired immediately.

           2 If the router has a current (*,G), or (*,*,RP), route
             entry, and if the existing (Sp,G) entry has its RPT-bit
             flag set to 1, then this (Sp,G)RPT-bit entry is maintained
             (not deleted) even if its outgoing interface list is null.

      2 For each address, Sp, in the prune list whose RPT-bit is
        set and whose WC-bit cleared:





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           1 If there is an existing (Sp,G) route entry, the router
             lowers the entry's Oif-timer for I to its Oif-Deletion-
             Delay, allowing for other downstream routers on a multi-
             access LAN to override the prune. However, on point-to-
             point links, the oif-timer is expired immediately.

           2 If the router has a current (*,G), or (*,*,RP), route
             entry, and if the existing (Sp,G) entry has its RPT-bit
             flag set to 1, then this (Sp,G)RPT-bit entry is not
             deleted, and the Entry-timer is restarted, even if its
             outgoing interface list is null.

           3 If (*,G), or corresponding (*,*,RP), state exists, but
             there is no (Sp,G) entry, an (Sp,G)RPT-bit entry is created
             . The outgoing interface list is copied from the (*,G), or
             (*,*,RP), entry, with the interface, I, on which the prune
             was received, is deleted.  Packets from the pruned source,
             Sp, match on this state and are not forwarded toward the
             pruned receivers.

           4 If there exists a (Sp,G) entry, with or without the
             RPT-bit set, the oif-timer for I is expired, and the
             Entry-timer is restarted.

      3 For each address, Sp, in the prune list whose RPT-bit and
        WC-bit are both set:

           1 If there is an existing (*,G) entry, with Sp as the RP
             for G, the router lowers the entry's Oif-timer for I to its
             Oif-Deletion-Delay, allowing for other downstream routers
             on a multi-access LAN to override the prune. However, on
             point-to-point links, the oif-timer is expired immediately.

           2 If the corresponding (*,*,RP) state exists, but there
             is no (*,G) entry, a (*,G) entry is created. The outgoing
             interface list is copied from (*,*,RP) entry, with the
             interface, I, on which the prune was received, deleted.

           For any new (S,G), (*,G) or (*,*,RP) entry created by an
           incoming Join/Prune message, the SPT-bit is cleared (and if a
           Join/Prune-Suppression timer is used, it is left off.)

   If the entry has a Join/Prune-Suppression timer associated with it,
   and if the received Join/Prune does not indicate the router as its
   target, then the receiving router examines the join and prune lists
   to see if any addresses in the list `completely-match' existing
   (S,G), (*,G), or (*,*,RP) state for which the receiving router
   currently schedules Join/Prune messages. An element on the join or



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   prune list `completely-matches' a route entry only if both the
   addresses and RPT-bit flag are the same.  If the incoming Join/Prune
   message completely matches an existing (S,G), (*,G), or (*,*,RP)
   entry and the Join/Prune arrived on the iif for that entry, then the
   router compares the Holdtime included in the Join/Prune message, to
   its own [Join/Prune-Holdtime]. If its own [Join/Prune-Holdtime] is
   lower, the Join/Prune-Suppression-timer is started at the
   [Join/Prune-Suppression-Timeout]. If the [Join/Prune-Holdtime] is
   equal, the tie is resolved in favor of the Join/Prune Message
   originator that has the higher network layer address.  When the
   Join/Prune timer expires, the router triggers a Join/Prune message
   for the corresponding entry(ies).

3.3 Register and Register-Stop

   When a source first starts sending to a group its packets are
   encapsulated in Register messages and sent to the RP. If the data
   rate warrants source-specific paths, the RP sets up source specific
   state and starts sending (S,G) Join/Prune messages toward the source,
   with S in the join list.

3.3.1 Sending Registers and Receiving Register-Stops

   Register messages are sent as follows:

      1 When a DR receives a packet from a directly connected
        source, S, on the subnet containing the address S,

           1 If there is no corresponding (S,G) entry, and the
             router has RP-Set information, and the DR is not the RP for
             G, the DR creates an (S,G) entry with the Register-
             Suppression-timer turned off and the RP address set
             according to the hash function mapping for the
             corresponding group. The oif list is copied from existing
             (*,G) or (*,*,RP) entries, if they exist. The iif of the
             (S,G) entry is always excluded from the oif list. If there
             exists a (*,G) or (*,*,RP) entry, the DR sends a Join/Prune
             message towards the RP with S in the prune list and the
             RPT-bit set.

           2 If there is a (S,G) entry in existence, the DR simply
             restarts the corresponding Entry-timer.

           When a PMBR (e.g., a router that connects the PIM-SM region
           to a dense mode region running DVMRP or PIM-DM) receives a
           packet from a source in the dense mode region, the router





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           treats the packet as if it were from a directly connected
           source. A separate document will describe the details of
           interoperability.

      2 If the new or previously-existing (S,G) entry's Register-
        Suppression-timer is not running, the data packet is
        encapsulated in a Register message and unicast to the RP for
        that group. The data packet is also forwarded according to (S,G)
        state in the DR if the oif list is not null; since a receiver
        may join the SP-tree while the DR is still registering to the
        RP.

      3 If the (S,G) entry's Register-Suppression-timer is running,
        the data packet is not sent in a Register message, it is just
        forwarded according to the (S,G) oif list.

   When the DR receives a Register-Stop message, it restarts the
   Register-Suppression-timer in the corresponding (S,G) entry(ies) at
   [Register-Suppression-Timeout] seconds. If there is data to be
   registered, the DR may send a null Register (a Register message with
   a zero-length data portion in the inner packet) to the RP, [Probe-
   Time] seconds before the Register-Suppression-timer expires, to avoid
   sending occasional bursts of traffic to an RP unnecessarily.

3.3.2 Receiving Register Messages and Sending Register-Stops

   When a router (i.e., the RP) receives a Register message, the router
   does the following:

      1 Decapsulates the data packet, and checks for a
        corresponding (S,G) entry.

           1 If a (S,G) entry with cleared (0) SPT bit exists, and
             the received Register does not have the Null-Register-Bit
             set to 1, the packet is forwarded; and the SPT bit is left
             cleared (0). If the SPT bit is 1, the packet is dropped,
             and Register-Stop messages are triggered.  Register-Stops
             should be rate-limited (in an implementation-specific
             manner) so that no more than a few are sent per round trip
             time. This prevents a high datarate stream of packets from
             triggering a large number of Register-Stop messages between
             the time that the first packet is received and the time
             when the source receives the first Register-Stop.

           2 If there is no (S,G) entry, but there is a (*,G)
             entry, and the received Register does not have the Null-
             Register-Bit set to 1, the packet is forwarded according to
             the (*,G) entry.



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           3 If there is a (*,*,RP) entry but no (*,G) entry, and
             the Register received does not have the Null-Register-Bit
             set to 1, a (*,G) or (S,G) entry is created and the oif
             list is copied from the (*,*,RP) entry to the new entry.
             The packet is forwarded according to the created entry.

           4 If there is no G or (*,*,RP) entry corresponding to G,
             the packet is dropped, and a Register-Stop is triggered.

           5 A "Border bit" bit is added to the Register message,
             to  facilitate  interoperability mechanisms. PMBRs set this
             bit when   registering for  external  sources  (see Section
             2.7).  If  the  "Border bit" is set in the Register,
             the   RP does the following:

                1 If there is no matching (S,G) state, but ther