How does a Level 1 IS-IS router reach destinations outside its own area?
A.
through the closest Level 1 router
B.
along the best path to the destination
C.
through the closest Level 1/2 router
D.
through the closest designated intermediate system (DIS)
Explanation:
When a router runs an L1 DIS election, it includes all neighbors with which it has an L1 adjacency, plus itself. Likewise, when a router runs an L2 DIS election, it considers all neighbors with which it has an L2 adjacency, plus itself. Remember that IS-IS considers two neighbors to be adjacent as soon as bidirectional communication is confirmed, whereas OSPF does not consider neighbors to be fully adjacent until their databases have been synchronized. This accounts for the difference in the prerequisite neighbor states for DIS/DR election.