Refer to the exhibit. Why is the neighbor relationship between R2 and R4 shown as ES-IS?
A. because there is an MTU mismatch between R2 and R4
B. because interface S3/0 of R4 is configured as L1/L2
C. because interface S3/0 of R2 is configured as L1
D. because there is a hello interval mismatch between R2 and R4
Answer “A” is incorrect. The correct answer should be “C” – IS-IS L1 routers (such as router R2 on the picture) can only form adjacency with other L1 and L1/L2 routers in the SAME area. In this case R2 and R4 are in different areas – 49.0001 and 49.0002, respectively. This is why the IS-IS hello types and hence the command output is as shown.