Backup Interface

A backup interface is an interface that stays idle until certain circumstances occur; then it is activated.

Backup Interface

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R4(config)# interface serial


R4 (config-if)# backup interfa R4(config-if)# backup delay 1

bri0/0 30


r Time to Disconnect After Primary Is Active

_, Time Primary Is Down Before

Backup Is Activated

• Specifies BRI 0/0 as a backup interface for serial 0/0

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Cisco CCIE Prep v1.0—Module


This example shows R4's Basic Rate Interface (BRI) interface being used to backup its primary link, which is the serial 0/0 interface

The backup interface command is placed under the primary link. This is the link that needs to be backed up in case of failure. Here you are specifying that the interface backing up the primary link is bri0/0.

Next, specify how quickly the backup interface would be activated upon failure of the primary interface. In the scenario, the backup delay is configured for 10 seconds. The backup interface will come up 10 seconds after it notices the primary link has failed. The backup interface is also configured to disconnect 30 seconds after the primary link is again operational.

Testing the backup interface is a little more difficult. A simple shutdown of the interface will not cause the IOS software to see this as a link failure. To test the backup interface, you must physically remove the cable from the serial interface. This is not the case if the backup interface command is configured on a Frame Relay point-to-point subinterface. If the shutdown command is performed on the Frame Relay interface of the router on the other side of the Permanent Virtual Circuit (PVC), it will cause the PVC to go "Inactive", causing the point-to-point subinterface to go down/down. This state will trigger the backup interface.

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