Exam 300-420 topic 1 question 169 discussion

How is Area0-R11 forming any adjacency with Area0-R1? It cant. L1 cannot form adjacency to L1/L2 from another area. Doing this in a lab, i get *Oct 7 01:00:02.864: ISIS-Adj: Area mismatch, level 1 IIH on GigabitEthernet0/0 *Oct 7 01:00:04.153: ISIS-Adj: Sending L1 LAN IIH on GigabitEthernet0/0, length 1497 *Oct 7 01:00:04.837: ISIS-Adj: Rec L2 IIH from 5254.001e.d934 (GigabitEthernet0/0), cir type L1L2, cir id 0000.0000.0011.01, length 1497, ht(30) *Oct 7 01:00:04.837: ISIS-Adj: is-type mismatch

C It's wrong because area 1 would not comunicate with area 0

R11 is L1

You cannot connect an L1 router to a L2 router so converting the entire Area to L2 will cause an issue between R1 and R11. Converting R3 into an L1/L2 provides the right solution.

Ok, u r right, but then u would be choosing 2 answers. As it to be just one, I would go with A, because it would make R3 a L1L2 router and, consequently, it would have also a L2 domain

This is a tricky question... because technically answers A and C will both work. I'm going with answer C because I'm assuming Area 0 here is a backbone area and as such best practice is to make all routers in the backbone area L2 only. Doing this prevents default routes from being propagated and creating sub-optimal routing.

Area 0 should be L2, R11 should be L2...

answer is correct. ENSLD 300-420 cert guide page 117. When creating a backbone there should never be L1 routers between (L2 only, or) L1/L2 routers.