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Difficulty: MediumFloating Static Routes

A network administrator needs to configure a floating static route on router R1 to serve as a backup path for the 192.168.100.0/24192.168.100.0/24 network. The primary path to this destination is currently learned dynamically via OSPF, which uses a default Administrative Distance of 110110. Which TWO statements correctly describe the requirements and operational behavior for this floating static route configuration?

  1. The floating static route must be configured with an Administrative Distance value greater than 110.Answer
  2. B
    The floating static route must be configured with an Administrative Distance value less than 110.
  3. The floating static route will only be installed into the routing table when the primary OSPF route disappears from the routing table.Answer
  4. D
    The floating static route will immediately enter the routing table alongside OSPF to enable load balancing.

Answer

The floating static route must be configured with an Administrative Distance greater than 110, and it will only be installed into the routing table after the primary OSPF route is removed.
A floating static route acts as an inactive backup line that only takes effect when the primary path goes down. Because Cisco IOS evaluates route preference using Administrative Distance (where lower is preferred), the backup static route must be configured with an AD higher than the primary protocol's AD (in this case, higher than OSPF's default AD of 110). Consequently, the backup route stays inactive in the background and is only installed into the IP routing table when the primary OSPF route is withdrawn.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
OSPF has a default AD of 110.
Administrative Distance defines route trustworthiness; lower values are preferred.
2
Determine the AD requirement for a backup (floating) static route.
The backup route AD must be strictly greater than 110 (e.g., 120).
If the AD were equal or lower, the router would prefer or load balance with the static route, preventing it from functioning strictly as a backup.
3
Analyze how Cisco IOS handles routing table selection with floating static routes.
The floating static route remains hidden from the routing table as long as the OSPF route (AD 110) exists.
When the primary OSPF route fails and is removed, the floating static route becomes the best available path for that destination prefix and is installed into the active routing table.

Key Concept

Floating Static Route AD Requirements and Routing Table Selection
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Topics

Floating Static Routes

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