CompTIA Network+ (N10-009)Network ImplementationHard
A network administrator has a primary route to the 10.20.0.0/16 network learned via OSPF. The administrator wants to configure a backup static route through a secondary ISP that will only be used if the OSPF route becomes unavailable. What administrative distance should be assigned to the static route?
- A90, matching EIGRP internal routes
- B115, a value higher than OSPF's default AD
- C1, the default for static routes
- D0, so the static route is always most preferred
Show answer & explanationAnswer & explanation
Correct answer: B. 115, a value higher than OSPF's default AD
To create a floating static route that only activates as a backup, its administrative distance must be set higher than the primary route's protocol AD (OSPF's default is 110). Setting the static route's AD to 115 ensures OSPF is preferred whenever it is available, with the static route only used if OSPF fails.
Why the other options are wrong
- A. An AD of 90 is lower than OSPF's 110 and would also always be preferred, defeating the backup purpose.
- C. An AD of 1 would make the static route preferred over OSPF at all times, not just as a backup.
- D. An AD of 0 is reserved for directly connected routes and would always override every other route.
Floating Static Route
A static route configured with an administrative distance higher than the primary dynamic routing protocol, so it only becomes active if the primary route fails.
- Default static route AD is 1, must be manually raised to float
- Must exceed the AD of the primary protocol (e.g., >110 for OSPF)
- Commonly used for backup ISP links or WAN failover
Memory trick: Float higher than the primary so it only kicks in when needed.