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Configuring IP Monitoring with Interface Failover

Using IP monitoring with interface failover, you can track an IP address or a set of IP addresses using a real-time performance monitoring (RPM) probe. If the RPM probe fails, you can enable a backup interface that is normally down in the steady state. After the RPM probe successfully reaches its target, the backup interface is again disabled.

Figure 1 shows the topology used in the configuration example and how IP monitoring works.

Figure 1: Real-Time Performance Monitoring TopologyReal-Time Performance Monitoring Topology

In the steady state, the interface fe-0/0/2 is in the link down state. However, when the RPM probes fail, the system enables the interface, and traffic flows through interface fe-0/0/2. When the RPM probes successfully reach their target, the system brings down interface fe-0/0/2 and traffic passes through fe-0/0/1.

To achieve this result, define an RPM probe to monitor IP address Enter the following configuration:

Also configure the IP monitoring policy to enable the backup interface fe-0/0/2 when the RPM probe fails. Enter the following configuration:

In this example, the interface fe-0/0/2 has a static IP address. Hence, you want to specify static routes to all destinations such that fe-0/0/2 is always the preferred route (lower preference value). You also need to specify routes to all destinations such that the next-hop router points to the next hop of fe-0/0/1 (higher preference value). With this approach, when interface fe-0/0/2 is disabled in the steady state, all traffic flows through fe-0/0/1. When interface fe-0/0/2 is up, all traffic flows through fe-0/0/2. Enter the following configuration:

If the backup interface has an IP address that is assigned using the Dynamic Host Configuration Protocol (DHCP), you do not know what the next hop through the backup interface is, and you are not able to add static routes similar to what is described previously. For more information about this scenario, see Configuring IP Monitoring with a DHCP Backup Interface.

In the steady state, you can reach IP address through the link with the IP address of, and the RPM probes are successful. The backup interface fe-0/0/2 is down. To verify the steady state, enter the following command:

In the following show command output, the PASS results in the Status field indicate that the probe is successful:

In the following show command output, the Probes sent count and Probes received count are equal, and the Loss percentage is 0. This indicates that the probe is successful.

When IP address is unreachable, the RPM probes fail and the interface fe-0/0/2 is enabled. All traffic is now routed through interface fe-0/0/2. The probes are still sent out of interface fe-0/0/1.

In the following show command output under the Results over current test: section, it shows the Probes sent count is 2 and the Probes received count is 0. It also shows that the Loss percentage is 100. This indicates that the probe has failed.

To further verify the fail state, use the following command:

To verify that interface fe-0/0/2 is enabled, use the following command:

To verify that IP address is now reachable through the device with the IP address of, use the following command:

When IP address is again reachable, the RPM probes successfully reach the target, and interface fe-0/0/2 is disabled. Now all traffic flows through interface fe-0/0/1.

To verify the operation of the restored steady state, use the following commands and verify that the results are similar to the steady-state results previously described: