300-420 Question 12
Select 3An enterprise network is designed using IS-IS as the Interior Gateway Protocol (IGP). The network spans multiple regions, and the design must ensure scalability, stability, and security. Which of the following design considerations should be implemented to achieve these goals?
- A
Deploy IS-IS multi-level hierarchy with Level 1 and Level 2 areas.
- B
Ensure that all routers in the network operate in Level 2-only mode to simplify routing.
- C
Implement route summarization between Level 1 and Level 2 areas.
- D
Enable authentication for IS-IS protocol exchanges.
- E
Avoid injecting external routes into IS-IS to reduce instability.
Show answer and explanation
Correct answers: A, C, D
Explanation
To create a stable, secure, and scalable IS-IS routing design, it is essential to leverage a multi-level hierarchy to manage topology size, implement route summarization to reduce routing overhead, and enable authentication for security. These practices collectively improve network scalability, stability, and security while maintaining efficient routing operations.
- A. Correct.
Deploying IS-IS multi-level hierarchy with Level 1 and Level 2 areas improves scalability by limiting the size of the topology database and reducing the scope of SPF calculations. This is a best practice for large networks.
- B. Incorrect.
Operating all routers in Level 2-only mode is not recommended in multi-level IS-IS deployments because it loses the benefits of hierarchy, such as reduced routing table size and better scalability.
- C. Correct.
Route summarization between Level 1 and Level 2 areas helps reduce the size of the routing table and limits the propagation of topology changes, contributing to both stability and scalability.
- D. Correct.
Enabling authentication for IS-IS protocol exchanges ensures secure routing operations by preventing unauthorized devices from participating in the IS-IS domain.
- E. Incorrect.
Avoiding external route injection entirely is not practical for most enterprise designs, as external routes are often necessary for interconnecting to other networks. However, proper filtering and summarization should be used instead.