Which two elements comprise the backbone area while designing a new network utilizing IS-IS as the interior gateway protocol

ccdp

#1

Which two elements comprise the backbone area while designing a new network utilizing IS-IS as the interior gateway protocol (choose two)

A. contiguous chain of Level 2 capable routers
B. contiguous chain of Level1/Level 2 capable routers
C. set of Level 2 configured interfaces
D. contiguous Level 1 capable routers
E. set of Level 1 configured interfaces

Correct Answer: AB

Explanation:
“Backbone IS-IS does not have a backbone area like the OSPF area 0. The IS-IS backbone is a contiguous collection of Level 2-capable routers, each of which can be in a different area” “In most designs with routing hierarchy, the Level 2 routers are also Level 1 routers by virtue of their identification with a certain area. Therefore, in IS-IS, a router can function as Level 1-only or Level 2-only and possibly as both Level 1 and Level 2 (Level 1-2). Level 1-2 routers act as border routers to their respective areas, providing connectivity to other areas. The Level 2 backbone is essentially a virtual IS-IS area consisting of routers engaged in Level 2 routing”