ZyXEL Communications 4528F User Manual

XGS-4526/4528F/4728F User’s Guide

This chapter introduces DVMRP and tells you how to configure it.

DVMRP (Distance Vector Multicast Routing Protocol) is a protocol used for routing 
multicast data within an autonomous system (AS). This DVMRP implementation is 
based on draft-ietf-idmr-dvmrp-v3-10. DVMRP provides multicast forwarding 
capability to a layer-3 switch that runs both the IPv4 protocol (with IP Multicast 
support) and the IGMP protocol. The DVMRP metric is a hop count of 32.

IGMP is a protocol used for joining or leaving a multicast group. You must have 
IGMP enabled when you enable DVMRP; otherwise you see the screen as in 

.

DVMRP uses the Reverse Path Multicasting (RPM) algorithm to generate an IP 
Multicast delivery tree. Multicast packets are forwarded along these multicast tree 
branches. DVMRP dynamically learns host membership information using Internet 
Group Management Protocol (IGMP). The trees are updated dynamically to track 
the membership of individual groups.

Initially an advertisement multicast packet is broadcast (“B” in the following 
figure). 

DVMRP-enabled Layer-3 devices that do not have any hosts in their networks that 
belong to this multicast group send back a prune message (“P”).

If hosts later join the multicast group, a graft message (“G”) to undo the prune is 
sent to the parent.