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Difficulty: MediumFloating Static Routes

An enterprise edge router receives its primary route to the 172.20.10.0/24172.20.10.0/24 destination network via OSPF, which uses a default Administrative Distance of 110110. A network administrator must configure a floating static backup route targeting next-hop IP address 192.168.12.2192.168.12.2 that will remain inactive in the routing table unless the primary OSPF route becomes unavailable. Which Cisco IOS command accomplishes this objective?

  1. ip route 172.20.10.0 255.255.255.0 192.168.12.2 120Answer
  2. B
    ip route 172.20.10.0 255.255.255.0 192.168.12.2 90
  3. C
    ip route 172.20.10.0 255.255.255.0 192.168.12.2 110
  4. D
    ip route 172.20.10.0 255.255.255.0 192.168.12.2 1

Answer

The command 'ip route 172.20.10.0 255.255.255.0 192.168.12.2 120' correctly configures the backup floating static route.
The correct command specifies an Administrative Distance of 120 at the end of the syntax. Because 120 is higher than the default OSPF distance of 110, Cisco IOS keeps this static route out of the routing table as long as the OSPF route is active. If the OSPF route fails and is withdrawn, the floating static route with AD 120 becomes the best available path and is inserted into the routing table.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary dynamic routing protocol.
OSPF has a default Administrative Distance of 110.
Floating static routes rely on AD values to determine route preference.
2
Determine the required Administrative Distance for the floating static route.
The static route AD must be strictly greater than 110 (e.g., 120).
Routers select routes with the lowest AD. Setting a higher value keeps the static route inactive while OSPF is healthy.
3
Construct the Cisco IOS static route command syntax.
The syntax is 'ip route <prefix> <mask> <next-hop> <distance>'. Placing 120 at the end sets the floating distance.
Specifying 120 at the end of the command overrides the default static AD of 1.

Key Concept

Floating Static Routes and Administrative Distance
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Topics

Floating Static Routes

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