Floating Static Route Not Activating After Primary Route Fails
Presenting Symptom
After the primary link fails, traffic is not forwarded via the floating static route, resulting in connectivity loss.
Network Context
A small branch office connects to the HQ via two WAN links: a primary T1 (Serial0/0/0) and a backup DSL (Serial0/0/1). The branch router (Cisco 4321, IOS 15.9) uses OSPF on the primary link and a floating static route with administrative distance 150 for the backup. When the primary link goes down, the floating static route does not appear in the routing table.
Diagnostic Steps
Check the routing table for the destination network
show ip route 10.0.0.0If primary is up: O 10.0.0.0/24 [110/2] via 192.168.1.1, 00:10:00, Serial0/0/0 If primary is down: no route shown
If no route appears after primary failure, the floating static route is not being installed. If the static route appears with wrong AD, check configuration.
Verify the floating static route configuration
show running-config | include ip route 10.0.0.0ip route 10.0.0.0 255.255.255.0 192.168.2.1 150
Confirm the static route exists with the correct administrative distance (150). If missing or wrong AD, it won't activate.
Check the status of the backup interface
show ip interface briefSerial0/0/1 up up
If the backup interface is down, the static route cannot be used. Ensure the interface is up/up.
Examine the routing table for the next-hop reachability
show ip route 192.168.2.1If reachable: S 192.168.2.0/24 [1/0] via ... or connected route If unreachable: no route
The floating static route requires the next-hop to be reachable via a connected or static route. If the next-hop is not in the routing table, the static route will not be installed.
Root Cause
The floating static route is configured with an administrative distance of 150, but the next-hop IP address (192.168.2.1) is not reachable because the backup interface (Serial0/0/1) is administratively down or the connected route is missing. Without a valid next-hop, the static route is not inserted into the routing table.
Resolution
Verification
After fix, run 'show ip route 10.0.0.0'. Expected output: S 10.0.0.0/24 [150/0] via 192.168.2.1. Also verify connectivity with ping 10.0.0.1.
Prevention
1. Always ensure backup interfaces are not administratively down and have correct IP addressing. 2. Use tracking objects (e.g., IP SLA) to dynamically adjust administrative distance based on reachability. 3. Document and test failover scenarios regularly.
CCNA Exam Relevance
On the CCNA 200-301 exam, this scenario tests understanding of floating static routes and administrative distance. Expect multiple-choice questions asking why a floating static route does not appear after primary route failure, or drag-and-drop to order troubleshooting steps. Key fact: A static route is only installed if the next-hop is reachable (connected route exists).
Exam Tips
Remember that a static route requires a reachable next-hop; if the exit interface is down, the route is not installed.
Administrative distance of a floating static route must be higher than the primary routing protocol (e.g., OSPF AD 110, so use >110).
Use 'show ip route static' to quickly view all static routes in the routing table.
Commands Used in This Scenario
show ip interface brief
Displays a summary of all IP interfaces on the device, including their IP address, status, and protocol state, used for quick verification of interface configuration and connectivity.
show ip route
Displays the current IP routing table on a Cisco router, used to verify routes, check next-hop addresses, and troubleshoot connectivity issues.
show running-config
Displays the current active configuration in DRAM, showing all non-default settings.
Test Your CCNA Knowledge
Practice with scenario-based questions to prepare for the CCNA 200-301 exam.
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