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Configuring IS-IS Levels on an Interface

You can administratively divide a single AS into smaller groups called areas. You configure each router interface to be in an area. Any interface can be in any area. The area address applies to the entire router; you cannot specify one interface to be in one area and another interface in a different area. In order to route between areas you must have two adjacent Level 2 routers that communicate with each other.
Level 1 routers can only route within their IS-IS area. To send traffic outside their area, Level 1 routers must send packets to the nearest intra-area Level 2 router. A router can be a Level 1 router, a Level 2 router, or both. You specify the router level on a per-interface basis, and a router becomes adjacent with other routers on the same level on that link only.

You can configure one Level 1 routing process and one Level 2 routing process on each interface, and you can configure the two levels differently.

To configure an area, include the level statement:




level level-number {

disable;

hello-authentication-key key;

hello-authentication-type authentication;

hello-interval seconds;

hold-time seconds;

ipv4-multicast-metric number;

ipv6-multicast-metric number;

ipv6-unicast-metric number;

metric metric;

passive;

priority number;

te-metric metric;
}

For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.

The statements within the level statement allow you to perform the following tasks when configuring the following optional level-specific properties:

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