Cisco CCNA (200-301)IP ConnectivityMedium
A company network uses OSPF as its primary routing protocol. An administrator wants to configure a backup path to the 192.168.10.0/24 network that should only be used if the OSPF-learned path becomes unavailable. The OSPF route has an administrative distance of 110. Which command correctly configures this backup path?
- A`ip route 192.168.10.0 255.255.255.0 10.0.0.5 permanent`
- B`ip route 192.168.10.0 255.255.255.0 10.0.0.5`
- C`ip route 192.168.10.0 255.255.255.0 10.0.0.5 120`
- D`ip route 192.168.10.0 255.255.255.0 10.0.0.5 100`
Show answer & explanationAnswer & explanation
Correct answer: C. `ip route 192.168.10.0 255.255.255.0 10.0.0.5 120`
To create a floating static route, its administrative distance must be higher than the primary route's administrative distance. Since OSPF has an AD of 110, a static route with an AD of 120 (like RIP's default AD, or any value greater than 110) will only be installed in the routing table if the OSPF route is no longer available.
Why the other options are wrong
- A. The `permanent` keyword keeps the route in the table even if the next hop is unreachable, but doesn't control its preference over other protocols based on AD.
- B. Without a specified AD, static routes default to an AD of 1, which would make it preferred over OSPF.
- D. An AD of 100 is lower than OSPF's 110, making this route preferred over OSPF.
Floating Static Route
A static route configured with an administrative distance higher than the primary route, ensuring it only becomes active if the primary route fails.
- Provides a backup path for a specific destination.
- Administrative Distance (AD) is key for its functionality.
- AD must be higher than the AD of the primary route.
- Only installed in the routing table if the primary route is removed.
Memory trick: Float a backup, when primary's down, with a higher AD crown.