isis hello-multiplier multiplier [level-1 | level-2]
no isis hello-multiplier [level-1 | level-2]
multiplier Integer value from 3 to 1000. The advertised hold time in IS-IS hello packets will be set to the hello multiplier times the hello interval. Neighbors will declare an adjacency to this router down after not having received any IS-IS hello packets during the advertised hold time. The hold time (and thus the hello multiplier and the hello interval) can be set on a per-interface basis, and can be different between different routers in one area.
Using a smaller hello multiplier will give fast convergence, but can result in more routing instability. Increment the hello multiplier to a larger value to help network stability when needed. Never configure a hello multiplier lower than the default value of 3.
level-1 (Optional) Configures the hello multiplier independently for Level 1 adjacencies. level-2 (Optional) Configures the hello multiplier independently for Level 2 adjacencies.
To specify the number of IS-IS hello packets a neighbor must miss before the router should declare the adjacency as down, use the isis hello-multiplier command in interface configuration mode. To restore the default value, use the no form of this command.
Level 1 and Level 2
The "holding time" carried in an IS-IS hello packet determines how long a neighbor waits for another hello packet before declaring the neighbor to be down. This time determines how quickly a failed link or neighbor is detected so that routes can be recalculated.
Use the isis hello-multiplier command in circumstances where hello packets are lost frequently and IS-IS adjacencies are failing unnecessarily. You can raise the hello multiplier and lower the hello interval (isis hello-interval command) correspondingly to make the hello protocol more reliable without increasing the time required to detect a link failure.
On point-to-point links, there is only one hello for both Level 1 and Level 2, so different hello multipliers should be configured only for multiaccess networks such as Ethernet and FDDI. Separate Level 1 and Level 2 hello packets are also sent over nonbroadcast multiaccess (NBMA) networks in multipoint mode, such as X.25, Frame Relay, and ATM. However, we recommend that you run IS-IS over point-to-point subinterfaces over WAN NBMA media.
In the following example, the network administrator wants to increase network stability by making sure an adjacency will go down only when many (ten) hello packets are missed. The total time to detect link failure is 60 seconds. This configuration will ensure that the network remains stable, even when the link is fully congested.Router(config)# interface serial 1 Router(config-if)# ip router isis Router(config-if)# isis hello-interval 6 level-1 Router(config-if)# isis hello-multiplier 10 level-1
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