Designing Cisco Network Service Architectures (ARCH, legacy) — Question 18

In which OSI layer does IS-IS operate?

Answer options

• A. Layer 1
• B. Layer 2
• C. Layer 3
• D. Layer 4

Correct answer: C

Explanation

IS-IS operates at Layer 3 of the OSI model, which is responsible for routing and forwarding packets between different networks. The other options, Layers 1, 2, and 4, pertain to physical transmission, data link, and transport functions respectively, and do not encompass the routing capabilities that IS-IS provides.