Modifying the PIM Hello Interval

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

When a routing device 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, the routing device sends out another hello message, and the timer is reset. A routing device 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 routing device would wait for a response is 105 seconds.

If a PIM hello message is received that contains the holdtime option, the neighbor timeout is set to the holdtime sent in the message. If a PIM hello message is received that does not contain the holdtime option, the neighbor timeout is set to the default hello holdtime.

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

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