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Difficulty: Very hardFloating Static Routes

Complete the Cisco IOS command below to configure a floating static route for the 172.16.100.0/22 network using the next-hop address 10.254.1.2. The route must serve as a floating backup to a primary path learned via internal EIGRP. Enter the dotted-decimal subnet mask in the first blank and the minimum integer administrative distance value required for backup operation in the second blank.

Answer:ip route 172.16.100.0 【255.255.252.0】 10.254.1.2 【91】

Answer

blank_1: 255.255.252.0, blank_2: 91
To configure a floating static route in Cisco IOS for the 172.16.100.0/22 prefix, the subnet mask must be specified in dotted-decimal format as 255.255.252.0. Internal EIGRP operates with a default Administrative Distance of 90. To ensure the static route acts strictly as a floating backup—entering the routing table only when the primary EIGRP route is lost—the static route must be assigned an Administrative Distance greater than 90. The minimum integer value that achieves this is 91.

Step-by-Step Solution

1
Convert the CIDR prefix length /22 to a dotted-decimal subnet mask.
A /22 prefix corresponds to 22 contiguous network bits (11111111.11111111.11111100.00000000), which equals 255.255.252.0.
Cisco IOS IPv4 static route syntax requires the subnet mask in dotted-decimal notation.
2
Identify the default Administrative Distance (AD) of internal EIGRP.
Internal EIGRP has a default AD of 90.
A floating static route must have an AD strictly greater than the primary route's AD to remain inactive in the routing table while the primary path is reachable.
3
Calculate the minimum administrative distance for the floating static route.
The minimum integer value greater than 90 is 91.
Assigning an AD of 91 ensures the static route is floating (inactive) relative to EIGRP (AD 90) but activates immediately if the EIGRP route fails.

Key Concept

Floating Static Route Configuration and Administrative Distance
Estimated Time:2m 0s
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Topics

Floating Static Routes

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