N10-009 Question 141
Single answerStatic routingA network administrator connects a small branch office to headquarters using a single WAN router. The branch office has one LAN subnet, 192.168.50.0/24, behind router BR1. Headquarters has several internal networks summarized as 10.0.0.0/8 behind router HQ1. BR1 and HQ1 are directly connected over a point-to-point link that uses 172.16.1.0/30, with BR1 at 172.16.1.2 and HQ1 at 172.16.1.1. Users at the branch can reach resources at headquarters after dynamic routing is temporarily enabled, but the company wants to return to a simple static-routing design. Which configuration on BR1 is the BEST choice to restore connectivity to all current and future headquarters subnets while keeping the branch configuration simple?
- A
Configure a static route on BR1 for 10.0.0.0/8 pointing to next-hop 172.16.1.1
- B
Configure a static route on BR1 for 192.168.50.0/24 pointing to next-hop 172.16.1.1
- C
Configure a default route on BR1 pointing to next-hop 192.168.50.1
- D
Configure a static route on BR1 for 172.16.1.0/30 pointing to next-hop 10.0.0.1
Show answer and explanation
Correct answer: A
Explanation
In a static-routing design, routers need routes only for networks that are not directly connected. BR1 already knows its local LAN and the 172.16.1.0/30 WAN link because those are connected networks. To reach headquarters, BR1 needs a route for the remote destination space behind HQ1. Since headquarters networks are summarized as 10.0.0.0/8, the most efficient static configuration on BR1 is a summary static route to 10.0.0.0/8 using HQ1's directly connected WAN IP, 172.16.1.1, as the next hop. This aligns with common routing best practices and vendor documentation from Cisco and similar platforms: use the next-hop address of the adjacent router for remote networks, prefer summarization where appropriate, and avoid adding static routes for directly connected networks. Although a default route can simplify branch configurations, the question asks specifically for the best choice to restore connectivity to headquarters subnets, and the provided default-route option is not valid because it uses the wrong next hop.
- A. Correct.
Correct. A static route for 10.0.0.0/8 via 172.16.1.1 tells BR1 to forward traffic for all headquarters internal networks to HQ1. Because headquarters networks are summarized as 10.0.0.0/8, this single route supports current and future subnets within that summary while keeping the branch configuration simple. Using the directly connected neighbor's IP as the next hop is standard practice for static routing on a point-to-point WAN link.
- B. Incorrect.
Incorrect. 192.168.50.0/24 is BR1's own local branch LAN subnet, so BR1 already knows how to reach it as a directly connected network. Adding a static route for its own LAN toward HQ1 would be unnecessary and could create incorrect forwarding behavior. This distractor reflects the misconception that every subnet in the environment must be statically defined on every router.
- C. Incorrect.
Incorrect. A default route can be valid in some branch-office designs, but this option points to 192.168.50.1, which is on the local LAN and would typically be a host or gateway interface behind BR1 rather than the upstream WAN next hop. A static route's next hop must be a reachable router in the direction of the destination, and in this scenario the correct upstream router is HQ1 at 172.16.1.1.
- D. Incorrect.
Incorrect. The 172.16.1.0/30 network is the directly connected WAN link between BR1 and HQ1, so BR1 already has a connected route for it. Also, pointing that route to 10.0.0.1 is invalid in this scenario because 10.0.0.1 is not identified as the adjacent next hop on the WAN segment. This distractor targets the misconception that transit networks require static routes even when directly connected.