Cisco CCNA (200-301)IP ConnectivityHard
A network uses EIGRP (AD 90) as its primary routing protocol. An administrator wants to configure a static backup route to the 172.20.0.0/16 network via 198.51.100.1 that is only used if the EIGRP route disappears from the routing table. Which command correctly creates this floating static route?
- Aip route 172.20.0.0 255.255.0.0 198.51.100.1 95
- Bip route 172.20.0.0 255.255.0.0 198.51.100.1 1
- Cip route 172.20.0.0 255.255.0.0 198.51.100.1
- Dip route 172.20.0.0 255.255.0.0 198.51.100.1 90
Show answer & explanationAnswer & explanation
Correct answer: A. ip route 172.20.0.0 255.255.0.0 198.51.100.1 95
A floating static route must have an administrative distance higher than the primary route's AD so it is only used as a backup. EIGRP's AD is 90, so the static route's configured AD must be greater than 90 (e.g., 95) to remain in the background and only become active if the EIGRP route is withdrawn.
Why the other options are wrong
- B. An AD of 1 would make the static route preferred over EIGRP, defeating the purpose of a backup route.
- C. Omitting the AD value defaults to AD 1, which would override the EIGRP route entirely instead of acting as backup.
- D. An AD of 90 equals EIGRP's AD, which could cause unpredictable tie behavior rather than acting strictly as backup.
Floating Static Route
A static route configured with an administrative distance higher than the primary dynamic routing protocol so it is only used as a backup path when the primary route is unavailable.
- Syntax: ip route <network> <mask> <next-hop> <AD>
- AD must be higher than the primary protocol's AD to float in the background
- Commonly used for backup WAN links or protocol failover
Memory trick: Set the AD higher so it floats below the primary route until needed.