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Difficulty: HardFloating Static Routes

Router R1 learns paths to remote subnet 192.168.100.0/24192.168.100.0/24 from two dynamic routing protocols: an Internal EIGRP path with an administrative distance of 90 and an OSPF path with an administrative distance of 110. An engineer must configure a floating static route pointing to next-hop 10.1.1.210.1.1.2 that remains dormant in the routing table and only activates if both dynamic paths fail. Which command must be configured on R1?

  1. ip route 192.168.100.0 255.255.255.0 10.1.1.2 115Answer
  2. B
    ip route 192.168.100.0 255.255.255.0 10.1.1.2 95
  3. C
    ip route 192.168.100.0 255.255.255.0 10.1.1.2 1
  4. D
    ip route 192.168.100.0 255.255.255.0 10.1.1.2 90

Answer

The command 'ip route 192.168.100.0 255.255.255.0 10.1.1.2 115' correctly configures the floating static route.
The correct command specifies an administrative distance of 115. Cisco IOS routers select routes for insertion into the routing table based on the lowest administrative distance. Because EIGRP has an AD of 90 and OSPF has an AD of 110, an AD value higher than 110 (such as 115) ensures the static route is ignored as long as either EIGRP or OSPF delivers a valid path. It will only be installed into the routing table as a floating backup when both dynamic routes are removed.

Step-by-Step Solution

1
Identify administrative distances of all active routing sources for destination 192.168.100.0/24
Internal EIGRP has AD = 90; OSPF has AD = 110.
Floating static routes rely on administrative distance values to dictate route installation hierarchy.
2
Determine the required administrative distance for the backup floating static route
The static route AD must be strictly greater than 110 (e.g., 115).
To ensure the static route activates only when BOTH dynamic paths (AD 90 and AD 110) are lost, its AD must exceed the highest AD of the active primary dynamic routes.
3
Select the command matching the syntax 'ip route <prefix> <mask> <next-hop> <distance>'
'ip route 192.168.100.0 255.255.255.0 10.1.1.2 115'
This command specifies destination 192.168.100.0/24 via next-hop 10.1.1.2 with an administrative distance of 115.

Key Concept

Floating Static Route Administrative Distance Selection
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Topics

Floating Static Routes

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