prune state remains until a host on the same VLAN issues a join for group "X", in which case the router cancels
the prune state and changes the flow to the forwarding state.
State-refresh packets and bandwidth conservation
A multicast switch, if directly connected to a multicast source (such as a video conference application),
periodically transmit state-refresh packets to downstream multicast routers. On routers that have pruned the
multicast flow, the state-refresh packets keep the pruned state alive. On routers that have been added to the
network after the initial flooding and pruning of a multicast group, the state-refresh packets inform the newly
added router of the current state of that branch. This means that if all multicast routers in a network support the
state-refresh packet, the multicast router directly connected to the multicast source performs only one flood-prune
cycle to the edge of the network when a new flow (multicast group) is introduced and preserves bandwidth for
other uses.
NOTE:
Some vendors' multicast routers do not offer the state-refresh feature. In this case, PIM-DM must
periodically advertise an active multicast group to these devices by repeating the flood/prune cycle
on the paths to such routers. For better traffic management in multicast-intensive networks where
some multicast routers do not offer the state-refresh feature, you may want to group such routers
where the increased bandwidth usage will have the least effect on overall network performance.
Figure 12: Bandwidth conservation in switches with PIM-DM state-refresh
General configuration elements
PM-DM requires you to configure the following elements:
• IP routing enabled on all routing switches you want to carry routed multicast traffic.
• Routing methods needed to reach the interfaces (VLANs) on which you want multicast traffic available for
hosts in your network:
◦ Enable RIP or OSPF at both the global and VLAN levels on the routers where there are connected hosts
that may issue multicast joins.
◦ Configure static routes to and from the destination subnets.
• Enable IP multicast routing.
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Aruba 3810 / 5400R Multicast and Routing Guide for ArubaOS-
Switch 16.08