Changing the frequency at which the routing switch transmits PIM hello messages on the current VLAN


ip pim-dense [hello-interval 5-30] 
 vlan [vid]ip pim-dense [hello-interval 5-30]

Changes the frequency at which the routing switch transmit PIM hello messages on the current VLAN. The routing switch uses hello packets to inform neighboring routers of its presence. The routing switch also uses this setting to compute the hello hold time, which is included in hello packets sent to neighbor routers. hello hold time tells neighbor routers how long to wait for the next hello packet from the routing switch. If another packet does not arrive within that time, the router removes the neighbor adjacency on that VLAN from the routing table, which removes any flows running on that interface.

Shortening the hello interval reduces the hello hold time. This has the effect of changing how quickly other routers will stop sending traffic to the routing switch if they do not receive a new hello packet when expected.


Not used with the [no]form of the ip pim-dense command.


If multiple routers are connected to the same VLAN and the routing switch requests multicast traffic, all routers on the VLAN receive that traffic. (Those that have pruned the traffic will drop it when they receive it.)

If the upstream router loses contact with the routing switch receiving the multicast traffic (that is, fails to receive a hello packet when expected), the shorter hello interval causes it to stop transmitting multicast traffic onto the VLAN sooner, resulting in less unnecessary bandwidth usage.