Changing the interval for PIM-SM neighbor notification


ip pim-sparse hello-interval [5-300] 
 vlan vid ip pim-sparse hello-interval [5-300]

Changes the frequency at which the router transmits PIM hello messages on the current VLAN. The router uses hello packets to inform neighbor routers of its presence.

The router 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 router. 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 changes how quickly other routers will stop sending traffic to the router if they do not receive a new hello packet when expected. For example, if multiple routers are connected to the same VLAN and the router 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 router 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 use.

(Default: 30 seconds)