Modifying the PIM Hello Interval

Routing devices send hello messages at a fixed interval on all PIM-enabled interfaces. By using hello messages, routing devices advertise their existence as PIM routing devices 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 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 another hello message, and the timer is reset. A routing device that receives 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 waits for a response is 105 seconds.

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

1. Configure the interface globally or in the routing instance. This example shows the configuration for the routing instance.
   [edit routing-instances PIM.master protocols pim interface fe-3/0/2.0]user@host# set hello-interval 255
2. Verify the configuration by checking the Hello Option Holdtime field in the output of the show pim neighbors detail command.
   user@host> show pim neighbors detail

   Instance: PIM.master
   Interface: fe-3/0/2.0
   Address: 192.168.195.37, IPv4, PIM v2, Mode: Sparse
   Hello Option Holdtime: 255 seconds
   Hello Option DR Priority: 1
   Hello Option LAN Prune Delay: delay 500 ms override 2000 ms
   Join Suppression supported
   Rx Join: Group Source Timeout
   225.1.1.1 192.168.195.78 0
   225.1.1.1 0
   
   Interface: lo0.0
   Address: 10.255.245.91, IPv4, PIM v2, Mode: Sparse
   Hello Option Holdtime: 255 seconds
   Hello Option DR Priority: 1
   Hello Option LAN Prune Delay: delay 500 ms override 2000 ms
   Join Suppression supported
   
   Interface: pd-6/0/0.32768
   Address: 0.0.0.0, IPv4, PIM v2, Mode: Sparse
   Hello Option Holdtime: 255 seconds
   Hello Option DR Priority: 0
   Hello Option LAN Prune Delay: delay 500 ms override 2000 ms
   Join Suppression supported