| DVMRP uses Reverse Path Forwarding. When a router receives a packet, it floods the packet out of all paths except the one that leads back to the packet's source. Data stream reaches all LANs (possibly multiple times). If a router is attached to a set of LANs that do not want to receive a particular multicast group, the router can send a "prune" message back up the distribution tree to stop subsequent packets from traveling where there are no members. |
| Since new hosts may want to join the multicast group at any time, DVMRP must periodically re-flood. This creates a scaling problem, especially if pruning not effective or not implemented. |