JNCIS-ENT: Juniper Networks Certified Specialist – Enterprise Routing and Switching (2025) — Question 21

You have two routers unable to form an IS-IS Level 1 adjacency.
Which two statements describe a reason for this problem? (Choose two.)

Answer options

• A. The MTU is set to 1500.
• B. Interface lo0 is not included as an IS-IS interface.
• C. The area numbers are different.
• D. The interfaces are on different subnets.

Correct answer: B, C

Explanation

The correct answers are B and C because if interface lo0 is not included as an IS-IS interface, it won't participate in the adjacency formation, and if the area numbers are different, the routers cannot communicate. Option A is incorrect because an MTU of 1500 is generally acceptable for IS-IS, and option D is wrong because routers can still form adjacencies across different subnets if they are within the same area.