Static RoutingCCNA 200-301

Floating Static Route Not Activating When Primary Fails

Presenting Symptom

The backup floating static route does not appear in the routing table when the primary route fails, causing loss of connectivity to the remote network.

Network Context

A small branch office connects to the headquarters via two WAN links: a primary T1 (Serial0/0/0) and a backup DSL (Serial0/0/1). The branch router (RouterB) has a static default route pointing to the T1 with administrative distance 1, and a floating static default route pointing to the DSL with administrative distance 200. When the T1 link goes down, the backup route does not activate, and the branch loses internet connectivity. Routers run IOS 15.9(3)M.

Diagnostic Steps

Check the routing table for the backup route

show ip route 0.0.0.0 0.0.0.0

Gateway of last resort is 10.1.1.1 to network 0.0.0.0
S*   0.0.0.0/0 [1/0] via 10.1.1.1, Serial0/0/0

Only the primary route is present. The backup floating static route (AD 200) is missing, even though the primary route's next-hop is unreachable.

Verify the floating static route configuration

show running-config | include ip route 0.0.0.0 0.0.0.0

ip route 0.0.0.0 0.0.0.0 10.1.1.1
ip route 0.0.0.0 0.0.0.0 192.168.2.1 200

Both static routes are configured. The backup route has AD 200, which is correct for a floating static route. The configuration appears correct.

Check the status of the primary interface

show interfaces Serial0/0/0

Serial0/0/0 is up, line protocol is up (looped)

The interface shows 'up' and 'looped'. This indicates a Layer 1/2 issue (loopback) that keeps the interface up but prevents proper routing. The router still considers the interface operational, so it does not remove the primary route, and the floating route never activates.

Verify the route's next-hop reachability

show ip route 10.1.1.1

Routing entry for 10.1.1.1/32
  Known via "connected", distance 0, metric 0 (connected)
  * directly connected via Serial0/0/0

The next-hop IP is directly connected and appears reachable because the interface is up. However, due to the loop, traffic may not actually reach the next-hop. The router does not perform end-to-end connectivity checks; it only checks interface status.

Root Cause

The primary interface (Serial0/0/0) is in a loopback state (line protocol shows 'looped'), causing the interface to remain up/up. The router considers the directly connected next-hop reachable because the interface is up, so it keeps the primary static route in the routing table. The floating static route with higher administrative distance does not activate because the primary route is still present. The loop condition prevents proper traffic forwarding but does not trigger route removal.

Resolution

1. Remove the loopback condition on the interface. This may require resolving a physical loop (e.g., cable loopback) or removing a loopback plug. 2. If the loop is intentional for testing, remove it: disconnect the loopback cable or disable loopback with 'no loopback' if configured. 3. Clear the routing table to force re-evaluation: 'clear ip route *' (optional, as routes will update when interface goes down). 4. If the interface is faulty, replace the cable or hardware. Commands: RouterB(config)# interface Serial0/0/0 RouterB(config-if)# no shutdown RouterB(config-if)# end RouterB# clear ip route *

Verification

1. Check interface status: 'show interfaces Serial0/0/0' should show 'Serial0/0/0 is up, line protocol is up' (no 'looped'). 2. Check routing table: 'show ip route 0.0.0.0 0.0.0.0' should show the backup route when the primary is down: S* 0.0.0.0/0 [200/0] via 192.168.2.1, Serial0/0/1 3. Test connectivity: ping to a remote destination should succeed.

Prevention

1. Use IP SLA tracking with static routes to monitor actual reachability of the next-hop, not just interface status. Configure a tracked object that sends ICMP echo to the next-hop and adjust the route's administrative distance based on the track state. 2. Implement Bidirectional Forwarding Detection (BFD) on serial interfaces for faster failure detection. 3. Regularly monitor interface status and errors; set up SNMP traps for interface state changes.

CCNA Exam Relevance

On the CCNA 200-301 exam, this scenario tests understanding of floating static routes and the conditions under which they activate. The exam may present a troubleshooting scenario where a backup route fails to appear, and you must identify that the primary interface is up but not functional (e.g., looped, err-disabled). Key fact: A floating static route only activates when the primary route is completely removed from the routing table, which requires the interface to go down or the next-hop to become unreachable via a routing protocol. The exam often includes a drag-and-drop or multiple-choice question asking why a floating route is not active.

Exam Tips

Remember that a floating static route will not activate if the primary route remains in the routing table, even if the primary path is broken. The router must lose the primary route first.

On the exam, look for interface status that is 'up/up' but with unusual conditions like 'looped' or 'err-disabled' — these can prevent route failover.

Know the 'show ip route' command and how to interpret administrative distance values. A floating static route typically uses an AD higher than the primary routing protocol (e.g., 200 for static vs 1 for directly connected).

Commands Used in This Scenario

show interfaces

Displays detailed status and statistics for all interfaces or a specific interface, used to verify interface operational state, errors, and performance.

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.

Practice CCNA Questions