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Difficulty: MediumIPv4 Static Routing

A border router receives a primary IPv4 route for destination network 198.51.100.0/24198.51.100.0/24 via external BGP (eBGP), which has an administrative distance of 2020. The network engineer must configure a backup floating static route via next-hop IPv4 address 203.0.113.5203.0.113.5 that remains inactive in the routing table unless the primary eBGP path becomes unavailable. Which command must be configured on the border router to achieve this requirement?

  1. ip route 198.51.100.0 255.255.255.0 203.0.113.5 25Answer
  2. B
    ip route 198.51.100.0 255.255.255.0 203.0.113.5 15
  3. C
    ip route 198.51.100.0 255.255.255.0 203.0.113.5 20
  4. D
    ip route 198.51.100.0 0.0.0.255 203.0.113.5 25

Answer

The command `ip route 198.51.100.0 255.255.255.0 203.0.113.5 25` correctly configures the backup floating static route.
To configure a floating static route as a backup to an eBGP-learned route (which has a default administrative distance of 2020), the static route must be assigned an administrative distance strictly greater than 2020. Setting the distance to 2525 ensures that Cisco IOS places the static route into the routing table only when the eBGP route is withdrawn. Additionally, Cisco IOS static route configuration requires a dotted-decimal subnet mask rather than a wildcard mask.

Step-by-Step Solution

1
Identify the administrative distance of the primary route protocol.
The primary route is learned via eBGP, which has a default administrative distance of 2020.
Cisco IOS selects routes with the lowest administrative distance for placement in the routing table.
2
Determine the required administrative distance for the backup route.
The administrative distance must be set to a value strictly greater than 2020 (such as 2525).
A higher administrative distance keeps the static route floating (inactive) in the background until the primary eBGP path drops.
3
Verify Cisco IOS IPv4 static route syntax requirements.
The syntax is `ip route <network-prefix> <subnet-mask> <next-hop-ip> [administrative-distance]`.
The command requires a standard subnet mask rather than an OSPF/ACL wildcard mask.

Key Concept

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

IPv4 Static Routing

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