RFC 1075 (rfc1075) - Page 2 of 24


Distance Vector Multicast Routing Protocol



Alternative Format: Original Text Document



RFC 1075       Distance Vector Multicast Routing Protocol  November 1988


   DVMRP differs from RIP in one very important way.  RIP thinks in
   terms of routing and forwarding datagrams to a particular
   destination.  The purpose of DVMRP is to keep track of the return
   paths to the source of multicast datagrams.  To make explanation of
   DVMRP more consistent with RIP, the word "destination" is used
   instead of the more proper "source", but the reader must remember
   that datagrams are not forwarded to these destinations, but originate
   from them.

   This memo is organized into the following sections:
           - A description of DVMRP is presented.
           - Tunnels are explained.
           - The routing algorithm is shown.
           - The forwarding algorithm is shown.
           - The various time values are listed.
           - Configuration information is specified.

   This memo does not analyze distance-vector routing, nor fully explain
   the distance-vector algorithm; see [1] for more information on these
   topics.  The process or processes that perform the routing and
   forwarding functions are called "routers" in this memo.

3. Protocol Description

   DVMRP uses the Internet Group Management Protocol (IGMP) to exchange
   routing datagrams [2].

   DVMRP datagrams are composed of two portions: a small, fixed length
   IGMP header, and a stream of tagged data.

   The fixed length IGMP header of DVMRP messages is:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version| Type  |  Subtype      |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The version is 1.

   The type for DVMRP is 3.

   The subtype is one of:

   1 = Response; the message provides routes to some destination(s).
   2 = Request; the message requests routes to some destination(s).
   3 = Non-membership report; the message provides non-membership
       report(s).



Waitzman, Partridge & Deering