Modifying the PIM Hello Interval

date_range 23-Nov-23

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

To modify how often the routing device sends hello messages out of an interface:

This example shows the configuration for the routing instance. Configure the interface globally or in the routing instance.
```
[edit routing-instances PIM.master protocols pim interface fe-3/0/2.0]
user@host# set hello-interval 255
```

Verify the configuration by checking the Hello Option Holdtime field in the output of the

show pim neighbors
detail

command.

content_copy zoom_out_map
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

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Multicast Protocols User Guide

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Modifying the PIM Hello Interval

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