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way like the RIP. That is to say, route advertisements are sent between DVMRP neighbors
periodically (every 60 seconds by default). The routing information in the DVMRP route
selection table is used to establish the source distribution tree, which can be used to
determine which neighbor can reach the source sending multicast information. Interfaces
leading to this neighbor are referred to as the upstream interface. Routing report packet
contains source network and the hops for assessing route metrics.
To forward properly, each DVMRP switch need to know in what specific interface the
multicast information should be received for the downstream switches. When a multicast
packet from a specific source is received, a DVMRP switch will first broadcast the
multicast packet in all downstream interfaces (interfaces in which other DVMRP switches
have indicated dependency). On receiving a prune message from a downstream switch,
that switch will be pruned. The DVMRP switch informs a upstream switch for a certain
source by poison reverse: “I am your downstream.” The DVMRP switch fulfills the poison
reverse by adding infinite (32) to the route metric of a certain source broadcasted by it in
replying its upstream switches. Hence correct metric value can be 1 to (2 x infinite (32) -1),
or 1 to 63. 1 to 31 indicates a reachable source network, 32 indicates an unreachable
source, 33 to 63 indicate the switch generating the report message depend on upstream
switches to receive multicast information from certain source.
16.5.2 DVMRP configuration
16.5.2.1 Configuration Task Sequence
1. Enable DVMRP (required)
2. Configure connectivity with CISCO routers/switches (optional)
3. Configure DVMRP sub-parameters (optional)
(1) Configuring DVMRP interface parameters.
a. Configure metric value for DVMRP report packet
b. Configuring DVMRP neighbor timeout time
(2) Configuring DVMRP global parameters.
a. Configure retransmission interval for graft packets in DVMRP
b. Configure transmission interval of probe packets in DVMRP
c. Configure transmission interval of report packets in DVMRP
d. Configuring DVMRP route timeout time
4. Configure DVMRP tunneling
5. Disable DVMRP
1. Enable DVMRP
Basic configuration of DVMRP routing protocol on route switch is quite simple: just enable
DVMRP in the appropriate interfaces.
Command Explanation
Interface Mode