level

In the IS-IS link-state protocol, level indicates the type of adjacency that can be formed between routers. Routers are assigned a capability for level 1, level 2, or both level 1 and 2. Level 1 routers can form adjacencies with other level 1-capable routers, and forward traffic within an area. Level 2 routers can form adjacencies with level 2-capable routers, and forward traffic between areas. Traffic that moves from one area to another is forwarded through routers that have both level 1 and 2 capability.