isis hello-interval

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.

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.
interface serial 0
isis hello-interval 5 level-1
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