Which two statements are correct about IS-IS? (Choose two.)

A Level 1 router can become adjacent with the Level 1 and Level 1-2 (L1/L2) router. A Level 2 router

can become adjacent with Level 2 or Level 1-2 (L1/L2) router. There is no adjacency between L1 only

and L2 only router. HOWEVER: If two routers are in different areas, they can only form a Level 2

adjacency. As such, two routers in different areas can NOT form a Level 1 adjacency. If you want two

routers to form a Level 1 adjacency, they have to be in the same area.

IS-IS (Intermediate System to Intermediate System) operates at two levels: Level 1 and Level 2. Level

1 routers are only aware of their own area's topology, while Level 2 routers have knowledge of the

topology across areas. A Level 1 router cannot form an adjacency with a Level 2 router unless the

Level 2 router is also operating as a Level 1 router (Level 1-2 router). Level 2 routers can form

adjacencies regardless of their area IDs because Level 2 operates at the domain level and is used to

interconnect different IS-IS areas.

Reference:

Juniper Networks Technical Documentation on IS-IS

IS-IS Levels and Areas Explanation - Juniper Networks