Cisco Certified Support Technician (CCST) NetworkingIP ConnectivityMedium
A network administrator is troubleshooting an issue where a newly added static route is not being used by the router, even though the destination network is unreachable without it. The `show ip route` command output confirms the static route is present but traffic is still being dropped. Which of the following is the most likely reason the static route is not being used?
- AThe router's routing table has reached its maximum capacity for static routes.
- BThe static route is configured with a /24 subnet mask, which is too broad for the destination.
- CThe administrative distance of the static route is higher than a dynamically learned route to the same destination.
- DThe next-hop IP address specified in the static route is directly connected to the router.
Show answer & explanationAnswer & explanation
Correct answer: C. The administrative distance of the static route is higher than a dynamically learned route to the same destination.
Routers use administrative distance to determine the trustworthiness of routing information. If a dynamically learned route (e.g., OSPF, EIGRP) exists for the same destination network with a lower administrative distance than a static route, the router will prefer the dynamic route, even if the static route is explicitly configured.
Why the other options are wrong
- A. While routing tables have limits, it's highly unlikely for a typical router to reach its maximum capacity for static routes in a small/medium network scenario, and it would usually indicate a different error or warning.
- B. A /24 subnet mask is a common and valid subnet mask; whether it's 'too broad' depends on the specific network, but it wouldn't inherently prevent the route from being used if it's the best path.
- D. A directly connected next-hop is a valid and often preferred configuration for static routes, not a reason for it to be unused.
Administrative Distance (AD)
A value used by routers to rate the trustworthiness of routing information received from a routing protocol or static configuration.
- Lower AD is preferred (0 is best, 255 means never trust).
- Directly connected routes have AD 0, static routes have AD 1.
- Used when a router learns about the same destination from multiple sources.
Memory trick: Routes compete in a trust contest; the most trustworthy wins.