Which two statements correctly describe IS-IS adjacencies? (Choose two.)
A.
Level 2 adjacencies can form within the same (intra) area only.
B.
Level 2 adjacencies can be established either interarea or intra-area.
C.
Level 1 adjacencies can form in the same (intra) area only.
D.
Level 2 adjacencies are formed between (inter) areas only.
Level 1 and Level 2 adjacencies can only form with either Level 1 or Level 2.
The correct answer here is A and C.
A router can be a Level 1 and a Level 2 router to join areas.
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B and C are right. Level 2 adjacency can be inter-area or intra-area
https://www.juniper.net/techpubs/en_US/junos16.1/topics/example/isis-multi-level.html
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Level 1 – 49.0001 (area 1) to Level 1 – 49.0001 (area 1) – formed
Level 1 – 49.0001 (area 1) to Level 1 – 49.0002 (area 2) – Not formed – two separate area’s.
Level 2 – 49.0001 (area 1) to Level 1 – 49.0001 (area 1) – Not formed – Level 1 can only form an adjacency to another Level 1 router in the same area.
Level 2 – 49.0001 (area 1) to Level 2 – 49.0001 (area 1) – formed
Level 2 – 49.0001 (area 1) to Level 2 – 49.0002 (area 2) – formed
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