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Difficulty: MediumFloating Static Routes

A network administrator is configuring a backup link on a Cisco router for destination network 10.50.0.0/2410.50.0.0/24. The primary path to this network is currently learned via OSPF, which has a default Administrative Distance (AD) of 110110. Which two statements correctly describe the requirements and operational behavior of the floating static route used for this backup path? (Select two.)

  1. The administrative distance configured at the end of the static route command must be greater than 110110.Answer
  2. B
    Setting the administrative distance of the static route to 9090 ensures it stays in standby mode until the OSPF neighbor relationship fails.
  3. The floating static route will only be installed into the active routing table if the primary OSPF route is removed.Answer
  4. D
    If no administrative distance is explicitly specified in the static route command, Cisco IOS automatically defaults to an administrative distance of 120120 when OSPF is running.

Answer

The floating static route must be configured with an administrative distance higher than the primary routing protocol's AD (greater than 110 for OSPF), and it will only populate the routing table when the primary OSPF route is removed.
A floating static route serves as a backup path by assigning an Administrative Distance (AD) higher than that of the primary routing protocol (OSPF AD = 110). Because Cisco IOS prefers routes with lower AD values, the floating static route is held in inactive standby and is only placed into the active routing table when the primary OSPF route disappears.

Step-by-Step Solution

1
Identify the primary routing protocol and its default Administrative Distance (AD).
The primary route is OSPF, which carries a default AD of 110110.
Administrative Distance determines the trustworthiness of routing sources in Cisco IOS.
2
Determine the required AD for the floating static route to function as a backup.
The static route AD must be set to a value higher than 110110 (such as 120120).
Lower AD values are preferred. Setting a higher AD ensures the static route is ignored as long as the OSPF route is present in the routing table.
3
Analyze how Cisco IOS installs the floating static route into the routing table.
The floating static route remains inactive in configuration until the OSPF route fails or is withdrawn, at which point the router installs the backup static route.
A router only installs the route with the lowest AD for a given prefix into the active routing table.

Key Concept

Floating Static Route Administrative Distance and Failover Mechanics
Estimated Time:1m 30s
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Topics

Floating Static Routes

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