Floating Static Routes – Detailed Explanation
🔹 Concept Checklist
- Definition of Floating Static Route
- Purpose as Backup Routes
- Use of Administrative Distance (AD) to control route preference
- Difference from regular static routes
- Configuration by manually setting higher AD
- Common use cases (redundancy, failover)
- Verification in routing tables
- Behavior when primary route fails
- Interaction with dynamic routing protocols
- Testing floating static routes under failure scenarios
- Troubleshooting tips
- Best practices for implementation
- Examples of AD values compared to other routes
1. Definition of Floating Static Route
A Floating Static Route is a static route configured with a higher administrative distance (AD) than the primary route. This causes it to be ignored under normal conditions. It "floats" in the routing table and only becomes active if the preferred (primary) route fails or disappears.
2. Purpose of Floating Static Routes
Floating static routes serve as backup routes to provide network redundancy and failover capabilities. They ensure continuous network availability by automatically taking over when the main route is down or unreachable.
3. How Floating Static Routes Use Administrative Distance (Higher AD)
Administrative Distance (AD) is a value that ranks route trustworthiness — the lower the AD, the higher the priority.
- Regular static routes have a default AD of
1. - Floating static routes are configured manually with a higher AD (e.g.,
10,100,200), so routers prefer routes with lower AD first. - The floating route activates only when routes with lower AD are no longer available.
4. Difference Between Floating Static Routes and Regular Static Routes
| Feature | Regular Static Route | Floating Static Route |
|---|---|---|
| Default AD | 1 | Manually configured (higher than primary) |
| Route Priority | Primary / always used if present | Backup / used only if primary fails |
| Usage | Normal routing | Redundancy and failover |
| Behavior when primary fails | N/A | Becomes active |
5. Configuring Floating Static Routes (Setting AD Value Manually)
Syntax:
ip route <destination> <mask> <next-hop-IP | interface> <administrative-distance>Example:
ip route 192.168.10.0 255.255.255.0 10.1.1.2 200
Here, the AD is set to 200, higher than the default 1, so this route is only used if no other route to 192.168.10.0/24 exists.
6. Use Cases of Floating Static Routes
- Redundancy: Provides backup paths if the primary link or route fails.
- Failover: Automatically switches traffic to the backup route without manual intervention.
- Hybrid Networks: Combines static routes with dynamic routing where static is used as backup.
- Remote Offices: Backup connection to a secondary ISP or link.
7. Verifying Floating Static Routes in Routing Table
Use the command:
show ip route
Floating static routes appear only if the primary route is absent or down.
When active, floating routes are indicated with an S (Static) and their administrative distance can be verified.
8. Behavior During Primary Route Failure
When the primary route (with lower AD) fails (due to interface down, next-hop unreachable, etc.), the router removes it from the routing table. Immediately, the floating static route (with higher AD) becomes the active route, forwarding traffic seamlessly.
9. Interaction with Dynamic Routing Protocols
Floating static routes are often used to back up dynamically learned routes (e.g., OSPF, EIGRP).
Since dynamic routes usually have AD values lower than the default static route (typically 90 for EIGRP, 110 for OSPF), floating static routes with higher AD remain inactive until those dynamic routes fail.
This approach is ideal in hybrid environments to ensure backup routes without complicating routing protocols.
10. Testing Floating Static Routes with Network Failures
- Verify the primary route is active using
show ip route. - Disable the primary interface or shut down the primary next-hop device.
- Observe the floating static route becoming active in the routing table.
- Ping or traceroute through the network to confirm failover path usage.
- Re-enable the primary path and verify that traffic returns to the primary route.
11. Troubleshooting Floating Static Routes
| Issue | Troubleshooting Tip |
|---|---|
| Floating route not activating | Verify AD values are correctly set; must be higher than the primary route's AD. |
| Primary route still preferred despite failure | Check route status and confirm primary route is truly down; check interface and next-hop reachability. |
| Traffic not failing over | Confirm failure conditions (e.g., interface down, ping failure to next-hop). |
| Routing loops or conflicts | Avoid overlapping static and dynamic routes that can cause instability. |
12. Best Practices When Implementing Floating Static Routes
- Assign an AD significantly higher than the primary route but not conflicting with other routing protocols.
- Use floating static routes only where backup routing is necessary to reduce routing table complexity.
- Test failover regularly to ensure proper operation.
- Document all static routes and their AD values clearly for maintenance and auditing.
- Combine floating static routes with network monitoring tools for better health visibility.
13. Examples of AD Values for Floating Static Routes Compared to Other Routes
| Route Type | Default AD | Typical Floating AD |
|---|---|---|
| Connected | 0 | N/A |
| Static | 1 | 10, 50, 100, 200 |
| EIGRP | 90 | N/A |
| OSPF | 110 | N/A |
| RIP | 120 | N/A |
Summary
Floating static routes provide a simple yet powerful mechanism for route redundancy and failover by leveraging the concept of administrative distance. They are easy to configure and ideal for networks requiring backup routes without deploying complex dynamic routing protocols.