Adjacency Formation in IS-IS
IS-IS routers form adjacencies based on the level of IS routing they are doing
and their area number. This is a CLNS adjacency and can be formed even if IP
addresses don�ft match.
�¡ Level 1 routers form adjacencies only with L1 and L1-2 devices in
their own area. (In Figure 4-1, R1 becomes adjacent with R2 and R3.)
�¡ Level 2 routers form adjacencies only with Level 2-capable devices
(either L2 or L1-2 routers). These can be in the local area or in other
areas. (In Figure 4-1, R6 becomes adjacent with R3 and R4.)
�¡ Level 1-2 routers form Level 1 adjacencies with L1 routers in their
own area, and Level 2 adjacencies with routers in other areas. (In
Figure 4-1, R4 has a L1 adjacency with R5 and a L2 adjacency with R6.)