Editing IS-IS (section)

== Adjacency formation ==
Compared to OSPF, in IS-IS rules and conditions of adjacency formation are much simpler and mainly depend on the router level.

* L1 router cannot form any adjacency with L2 router under any conditions.
* L1 router can form L1 adjacency with other L1 router if their areas match.
* L1 router can form L1 adjacency with L1/L2 router if their areas match.
* L2 router can form L2 adjacency with other L2 router regardless of their areas (they don't need to match).
* L2 router can form only L2 adjacency with other L1/L2 router regardless of their areas (they don't need to match).
* L1/L2 router can form both L2 and L1 adjacency with other L1/L2 router if their areas match.