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Difficulty: Very hardFloating Static Routes

An enterprise router displays the following output in its routing table:

text
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O 10.45.0.0/16 [110/20] via 192.168.1.1, 00:04:12, GigabitEthernet0/0

A network administrator needs to configure a backup floating static route to destination prefix 10.45.0.0/1610.45.0.0/16 via next-hop IP 192.168.2.1192.168.2.1. The backup route must remain inactive in the routing table until the primary OSPF route becomes unavailable. Which command must be configured on the router to fulfill this requirement?

  1. ip route 10.45.0.0 255.255.0.0 192.168.2.1 120Answer
  2. B
    ip route 10.45.0.0 255.255.0.0 192.168.2.1 100
  3. C
    ip route 10.45.0.0 255.255.0.0 192.168.2.1
  4. D
    ip route 10.45.0.0 255.255.0.0 192.168.2.1 110

Answer

The command 'ip route 10.45.0.0 255.255.0.0 192.168.2.1 120' correctly configures the floating static route.
The active route to network 10.45.0.0/1610.45.0.0/16 is learned via OSPF, which has an Administrative Distance of 110. To create a floating static route that serves strictly as a backup, the static route must be configured with an Administrative Distance strictly greater than 110. Specifying a distance of 120 keeps the route out of the routing table while OSPF is functional, and allows Cisco IOS to automatically insert the static route if OSPF fails.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the active primary route.
The routing table shows OSPF route [110/20], indicating a default Administrative Distance of 110110 for OSPF.
Floating static routes rely on Administrative Distance comparison to determine installation eligibility in the routing table.
2
Determine the required Administrative Distance for a floating static backup route.
The backup static route must have an AD strictly greater than 110110 (such as 120120).
Cisco IOS installs the route with the lowest Administrative Distance. Setting a higher AD keeps the static route floating in configuration without entering the active routing table until the primary route fails.
3
Formulate the correct Cisco IOS static route command syntax.
ip route 10.45.0.0 255.255.0.0 192.168.2.1 120
The trailing argument in the 'ip route' command defines the custom Administrative Distance.

Key Concept

Floating Static Route Administrative Distance Selection
Estimated Time:1m 30s
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Topics

Floating Static Routes

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