To implement IS-IS in your network, you must enable IS-IS on each participating routers.
To assign different level capabilities to the routers and organize your network into areas, modify the level capability defaults on end systems from Level 1/2 to Level 1. Routers communicating to other areas can retain the Level 1/2 default.
On each router, at least one area ID also called the area address should be configured as well as at least one IS-IS interface:
Enable IS-IS.
Configure global IS-IS parameters.
Configure area addresses.
Configure IS-IS interface-specific parameters.