Command:

isis hello-interval


Mode:

Router(config-if)#


Syntax:

isis hello-interval {seconds | minimal} [level-1 | level-2]
no isis hello-interval [level-1 | level-2]

 

Syntax Description:

seconds An integer value. By default, a value three times the hello interval seconds is advertised as the hold time in the hello packets sent. (Change the multiplier of 3 by specifying the isis hello-multiplier command.) With smaller hello intervals, topological changes are detected faster, but there is more routing traffic. The default is 10 seconds.
minimal Causes the system to compute the hello interval based on the hello multiplier (specified by the isis hello-multiplier command) so that the resulting hold time is 1 second.
level-1 (Optional) Configures the hello interval for Level 1 independently. Use this on X.25, Switched Multimegabit Data Service (SMDS), and Frame Relay multiaccess networks.
level-2 (Optional) Configures the hello interval for Level 2 independently. Use this on X.25, SMDS, and Frame Relay multiaccess networks.

 

Command Description:

To specify the length of time between hello packets that the Cisco IOS software sends, use the isis hello-interval command in interface configuration mode. To restore the default value, use the no form of this command.

Defaults:
10 seconds
Level 1 and Level 2

The hello interval multiplied by the hello multiplier equals the hold time. If the minimal keyword is specified, the hold time is 1 second and the system computes the hello interval based on the hello multiplier.

The hello interval can be configured independently for Level 1 and Level 2, except on serial point-to-point interfaces. (Because only a single type of hello packet is sent on serial links, it is independent of Level 1 or Level 2.) The level-1 and level-2 keywords are used on X.25, SMDS, and Frame Relay multiaccess networks or LAN interfaces.

A faster hello interval gives faster convergence, but increases bandwidth and CPU usage. It might also add to instability in the network. A slower hello interval saves bandwidth and CPU. Especially when used in combination with a higher hello multiplier, this configuration may increase overall network stability.

It makes more sense to tune the hello interval and hello multiplier on point-to-point interfaces than on LAN interfaces.


Example:

The following example configures serial interface 0 to advertise hello packets every 5 seconds. The router is configured to act as a station router. This configuration will cause more traffic than configuring a longer interval, but topological changes will be detected earlier.

Router(config)# interface serial 0
Router(config-if)# isis hello-interval 5 level-1


Misconceptions:

None


Related Commands:

isis hello-multiplier

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