Cisco CCNA (200-301)IP ConnectivityEasy
A router has learned a route to 172.16.5.0/24 from three different sources: a directly configured static route, RIP, and OSPF, all pointing toward the same next hop. With default administrative distances and no other configuration, which route will be installed in the routing table?
- AThe OSPF route, because it is a link-state protocol
- BThe static route, because it has the lowest administrative distance
- CAll three routes are installed as equal-cost paths
- DThe RIP route, because it converges fastest
Show answer & explanationAnswer & explanation
Correct answer: B. The static route, because it has the lowest administrative distance
Administrative distance (AD) ranks the trustworthiness of a route source when multiple sources advertise the same prefix. Static routes have a default AD of 1, OSPF is 110, and RIP is 120, so the static route wins.
Why the other options are wrong
- A. OSPF's AD (110) is higher than the static route's AD (1).
- C. Only one route per prefix is installed unless AD and prefix are identical for equal-cost paths from the same protocol.
- D. Convergence speed does not determine which route is installed; AD does.
Administrative Distance
A value from 0-255 that ranks the trustworthiness of a routing information source; lower is more preferred.
- Connected=0, Static=1, EIGRP=90, OSPF=110, RIP=120
- Only used when multiple sources have a route to the SAME prefix length
- Longest prefix match is checked before AD
Memory trick: Lower AD number = higher trust, like golf scoring.