rfc1075.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Waitzman, Partridge & Deering                                   [Page 6]

RFC 1075       Distance Vector Multicast Routing Protocol  November 1988


3.8 Requested Destination Address (RDA) Command

   Format:  0 1 2 3 4 5 6 7    0 1 2 3 4 5 6 7
           +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+
           |        8      |  |     count     |
           +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+

   Array of 'count' additional arguments, with AFI = IP:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Requested Destination Address1                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Requested Destination Address2                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Count is the number of addresses supplied, from 0 to 255.  The length
   of the addresses depends upon the current address family.  The number
   of addresses supplied is subject to the message length limitation of
   512 bytes.

   Default: None.

   Description: The RDA command provides a list of destinations for whom
   routes are requested.  A routing request for all routes is encoded by
   using a count = 0.

3.9 Non Membership Report (NMR) Command

   Format:  0 1 2 3 4 5 6 7    0 1 2 3 4 5 6 7
           +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+
           |        9      |  |     count     |
           +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+

    Array of 'count' additional arguments, with AFI = IP:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Multicast Address1                                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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RFC 1075       Distance Vector Multicast Routing Protocol  November 1988


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Hold Down Time1                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Multicast Address2                                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Hold Down Time2                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Count is the number of Multicast Address and Hold Down Time pairs
   supplied, from 1 to 255.  The length of the addresses depends upon
   the current address family.  The number of pairs supplied is subject
   to the message length limitation of 512 bytes.

   Default: None.

   Description: The NMR command is experimental, and has not been tested
   in an implementation.  Each multicast address and hold down time pair
   is called a non-membership report.  The non-membership report tells
   the receiving router that the sending router has no descendent group
   members in the given group.  Based on this information the receiving
   router can stop forwarding datagrams to the sending router for the
   particular multicast address(es) listed.  The hold down time
   indicates, in seconds, how long the NMR is valid.

   It is an error for count to equal 0.

   The only other commands in a message that has NMR commands can be the
   AFI, flags0, and NULL commands.  No relevant flags for the flags0
   command are currently defined, but that may change in the future.

3.10 Non Membership Report Cancel (NMR Cancel) Command

   Format:  0 1 2 3 4 5 6 7    0 1 2 3 4 5 6 7
           +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+
           |       10      |  |     count     |
           +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+





Waitzman, Partridge & Deering                                   [Page 8]

RFC 1075       Distance Vector Multicast Routing Protocol  November 1988


    Array of 'count' additional arguments, with AFI = IP:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Multicast Address1                                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Multicast Address2                                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Count is the number of Multicast Addresses supplied, from 1 to 255.
   The length of the addresses depends upon the current address family.
   The number of addresses supplied is subject to the message length
   limitation of 512 bytes.

   Default: None.

   Description: The NMR Cancel command is experimental, and has not been
   tested in an implementation.  For each multicast address listed, any
   previous corresponding non-membership reports are canceled.  When
   there is no corresponding non-membership report for a given multicast
   address, the Cancel command should be ignored for that multicast
   address.

   It is an error for count to equal 0.

   The only other commands in a message that has NMR Cancel commands can
   be the AFI, flags0, and NULL commands.  No relevant flags for the
   flags0 command are currently defined, but that may change in the
   future.

3.12 Examples (with bytes in '{}'), not including the message header:

3.12.1 Supplying a single route to the IP address 128.2.251.231 with
   a metric of 2, an infinity of 16, a subnetmask of 255.255.255.0:

   Subtype 1,
   AFI 2,  Metric 2, Infinity 16, Subnet Mask 255.255.255.0
   {2} {2} {4} {2}   {6} {16}     {3} {1} {255} {255} {255} {0}

   DA Count=1 [128.2.251.231]
   {7} {1} {128} {2} {251} {231}





Waitzman, Partridge & Deering                                   [Page 9]

RFC 1075       Distance Vector Multicast Routing Protocol  November 1988


3.12.2 Supplying a route to the IP addresses 128.2.251.231 and
   128.2.236.2 with a metric of 2, an infinity of 16, a subnetmask of
   255.255.255.0:

   Subtype 1,
   AFI 2,  Metric 2, Infinity 16, Subnet Mask 255.255.255.0
   {2} {2} {4} {2}   {6} {16}     {3} {1} 255} {255} {255} {0}

   DA Count=2 [128.2.251.231] [128.2.236.2]
   {7} {1} {128} {2} {251} {231} {128} {2} {236} {2}

3.12.3 Request for all routes to IP destinations.

   Subtype 2, AFI 2,  RDA Count = 0
              {2} {2} {8} {0}

3.12.4 Non Membership Report for groups 224.2.3.1 and 224.5.4.6 with a
   hold down time of 20 seconds, and group 224.7.8.5 with a hold down
   time of 40 seconds.

   Subtype 3,
   AFI 2,  NMR Count = 3 [224.2.3.1, 20]
   {2} {2} {10} {3} {224} {2} {3} {1} {0} {0} {0} {20}

   [224.5.4.6, 20] [224.7.8.5, 40]
   {224} {5} {4} {6} {0} {0} {0} {20} {224} {7} {8} {5} {0} {0} {0} {40}

3.13 Summary of Commands


   Value   Name            Other commands allowed in same message
   -----   ----            ---------------------------------------
   0       Null            Null, AFI, Subnetmask, Metric, Flags0,
                           Infinity, DA, RDA, NMR, NMR-cancel

   2       AFI             Null, AFI, Subnetmask, Metric, Flags0,
                           Infinity, DA, RDA, NMR, NMR-cancel

   3       Subnetmask      Null, AFI, Subnetmask, Metric, Flags0,
                           Infinity, DA, RDA

   4       Metric          Null, AFI, Subnetmask, Metric, Flags0,
                           Infinity, DA

   5       Flags0          Null, AFI, Subnetmask, Metric, Flags0,
                           Infinity, DA





Waitzman, Partridge & Deering                                  [Page 10]

RFC 1075       Distance Vector Multicast Routing Protocol  November 1988


   6       Infinity        Null, AFI, Subnetmask, Metric, Flags0,
                           Infinity, DA

   7       DA              Null, AFI, Subnetmask, Metric, Flags0,
                           Infinity, DA

   8       RDA             Null, AFI, Subnetmask, Flags0, RDA

   9       NMR             Null, AFI, Flags0, NMR

   10      NMR-cancel      Null, AFI, Flags0, NMR-cancel


4. Tunnels

   A tunnel is a method for sending datagrams between routers separated
   by gateways that do not support multicasting routing.  It acts as a
   virtual network between two routers.  For instance, a router running
   at Stanford, and a router running at BBN might be connected with a
   tunnel to allow multicast datagrams to traverse the Internet.  We
   consider tunnels to be a transitional hack.

   Tunneling is done with a weakly encapsulated normal multicasted
   datagram.  The weak encapsulation uses a special two element IP loose
   source route [5].  (This form of encapsulation is preferable to
   "strong" encapsulation, i.e., prepending an entire new IP header,
   because it does not require the tunnel end-points to know each
   other's maximum reassembly buffer size.  It also has the benefit of
   correct behavior of the originator's time-to-live value and any other
   IP options present.)

   A tunnel has a local end-point, remote end-point, metric, and
   threshold associated with it.  The routers at each end of the tunnel
   need only agree upon the local and remote end-points.  See section 8
   for information on how tunnels are configured.  Because the number of
   intermediate gateways between the end-points of a tunnel is unknown,
   additional research is needed to determine appropriate metrics and
   thresholds.

   To send a datagram on a tunnel, the following occurs:

      - A null IP option is inserted into the datagram.  This provides
        preferred alignment for the loose source route IP option.

      - A two element loose source route IP option is inserted into
        the datagram.

      - The source route pointer is set to point to the second element



Waitzman, Partridge & Deering                                  [Page 11]

RFC 1075       Distance Vector Multicast Routing Protocol  November 1988


        in the source route.

      - The first element in the source route is replaced with the
        address of the originating host (the original IP source
        address).

      - The second element in the source route is replaced with the
        multicast destination address provided by the originating host
        (the original IP destination address).

      - The IP source address is replaced with the address of the
        router's appropriate outgoing physical interface (the local
        tunnel end-point).

      - The IP destination address is replaced with an address of the
        remote router (the remote tunnel end-point).

      - The datagram is transmitted to the remote router using
        non-multicast routing algorithms.

   Intermediate, non-multicast gateways will route the tunneled datagram
   to the remote tunnel end-point.  Because the datagram's IP source
   address has been replaced with the address of the local tunnel end-
   point, ICMP error messages will go to the originating multicast
   router.  This behavior is desired, because a host that sends a
   multicast datagram, which a multicast router decides to tunnel,
   should not be aware of the use of the tunnel.  If the datagram's IP
   source address were not changed when encapsulating the datagram, any
   ICMP errors would be sent to the originating host.

   When the remote tunnel end-point receives the tunneled datagram, the
   following occurs:

      - The IP source address is replaced with the first element in the
        loose source route.

      - The IP destination address is replaced with the second element
        in the loose source route.

      - The null option and the loose source route option are removed
        from the datagram.  This is needed because a host should not
        be able to tell that it has received a datagram that was sent
        through a tunnel.

   Because no specific network is associated with a tunnel, there are no
   local group memberships to be tracked for a tunnel.  The only
   neighbor on a tunnel can be the remote end-point.  Routing messages
   should be exchanged through tunnels, but a route is not created for a



Waitzman, Partridge & Deering                                  [Page 12]