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Modifying the Hello Interval

Routers send hello messages at a fixed interval on all PIM-enabled interfaces. Using hello messages, routers advertise their existence as a PIM router on the subnet. With all PIM-enabled routers advertised, a single DR for the subnet is established.

When a router is configured for PIM, it sends out a hello message at a 30-second default interval. The interval range is from 0 through 255. When the interval counts down to 0, it sends out another hello message, and the timer is reset. A router that gets no response from a neighbor in 3.5 times the interval value drops the neighbor. In the case of a 30-second interval, the amount of time a router would wait for a response is 105 seconds.

To modify how often the router sends hello messages out of an interface, include the hello-interval statement:




hello-interval seconds;

For a list of the hierarchy levels at which you can include this statement, see the statement summary section for this statement.

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