300-420 Question 120
Single answerAn enterprise network has multiple branch offices connected to the headquarters via a hub-and-spoke topology. Each branch office has been assigned a contiguous block of IP addresses, and the headquarters router is receiving individual routes for each subnet in these blocks via OSPF. This has resulted in a bloated routing table at the headquarters router. As the network engineer, how can you optimize the routing table at the headquarters while ensuring all branch subnets remain reachable?
- A
Configure manual route summarization on the branch routers to advertise a single summary route for their respective subnets.
- B
Enable OSPF supernetting on the headquarters router to automatically summarize routes.
- C
Configure route summarization on the headquarters router to aggregate routes received from all branch routers.
- D
Disable OSPF on the branch routers and use static routes to reduce the number of routes advertised.
Show answer and explanation
Correct answer: A
Explanation
Route summarization is a critical technique for optimizing routing tables, especially in large networks. In OSPF, summarization must be configured at the ABR or ASBR, or in this case, at the branch routers to summarize the subnets they advertise. This approach reduces the number of routes in the headquarters router's routing table while retaining reachability to all branch subnets.
- A. Correct.
Correct. Configuring manual route summarization on the branch routers allows each branch to advertise a single summary route for its subnets. This reduces the number of routes advertised to the headquarters router, optimizing its routing table while maintaining reachability to all subnets.
- B. Incorrect.
Incorrect. OSPF does not have a feature called 'supernetting' to automatically summarize routes. Route summarization must be configured manually in OSPF.
- C. Incorrect.
Incorrect. While summarization can be configured on the headquarters router in some protocols (e.g., BGP), OSPF requires summarization to be performed at the originating routers (in this case, the branch routers).
- D. Incorrect.
Incorrect. Disabling OSPF and using static routes is not a scalable or recommended solution, as it increases administrative overhead and reduces the network's dynamic routing flexibility.