DELL N3000 User Manual

Managing IPv4 and IPv6 Multicast

router on its RPF interface, the State Refresh message causes an existing 

prune state to be refreshed. State Refresh messages are generated periodically 

by the router directly attached to the source.

DVMRP is an interior gateway protocol that is suitable for routing multicast 

traffic within an autonomous system (AS). DVMRP should not be used 

between different autonomous systems due to limitations with hop count and 

scalability.

DVMRP exchanges probe packets with all its DVMRP-enabled routers, it 

establishes two-way neighboring relationships, and it builds a neighbor table. 

DVMRP exchanges report packets and creates a unicast topology table, with 

which it builds the multicast routing table. This table is used to route the 

multicast packets. Since every DVMRP router uses the same unicast routing 

protocol, routing loops are avoided.

DVMRP is based on RIP; it forwards multicast datagrams to other routers in 

the AS and constructs a forwarding table based on information it learns in 

response. More specifically, it uses this sequence.

• A new multicast packet is forwarded to the entire multicast network, with 

respect to the time-to-live (TTL) of the packet.

• The TTL restricts the area to be flooded by the message.
• All routers that do not have members on directly-attached subnetworks 

send back 

Prune messages to the upstream router.

• The branches that transmit a prune message are deleted from the delivery 

tree.

• The delivery tree which is spanning to all the members in the multicast 

group, is constructed in the form of a DVMRP forwarding table.

In addition to DVMRP, the switch supports the Protocol-Independent 

Multicast (PIM) sparse-mode (PIM-SM) and dense-mode (PIM-SM) routing 

protocol. Only one multicast routing protocol can be operational on the switch at 

any time. If you enable DVMRP, PIM must be disabled. Similarly, if PIM is enabled, 

DVMRP must be disabled.