Configuring Adjacency

You can configure the type (level) of adjacency you want to use on an IS-IS interface.

isis circuit-type

Use to specify adjacency levels on a specified interface; however, normally, you do not need to use this command.
Configure a router as a level 1-only, a level 1–level 2 system, or a level 2-only system.
Configure some interfaces to be level 2-only for routers that are between areas. This prevents wasting bandwidth by sending out unused level 1 hellos.
On point-to-point interfaces, the level 1 and level 2 hellos are in the same packet.
Level 1-2 is the default.
Example host1(config-if)#isis circuit-type level-2-only
Use the no version to restore the default value, level-1-2.
See isis circuit-type