Configuring a loopback interface
A loopback interface is a virtual interface. The physical layer state of a loopback interface is always up unless the loopback interface is manually shut down. Because of this benefit, loopback interfaces are widely used in the following scenarios:
Configuring a loopback interface address as the source address of the IP packets that the device generates—Because loopback interface addresses are stable unicast addresses, they are usually used as device identifications.
When you configure a rule on an authentication or security server to permit or deny packets that a device generates, you can simplify the rule by configuring it to permit or deny packets carrying the loopback interface address that identifies the device.
When you use a loopback interface address as the source address of IP packets, make sure the route from the loopback interface to the peer is reachable by performing routing configuration. All data packets sent to the loopback interface are considered packets sent to the device itself, so the device does not forward these packets.
Using a loopback interface in dynamic routing protocols—With no router ID configured for a dynamic routing protocol, the system selects the highest loopback interface IP address as the router ID. In BGP, to avoid interruption of BGP sessions due to physical port failure, you can use a loopback interface as the source interface of BGP packets.
To configure a loopback interface:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Create a loopback interface and enter loopback interface view. | interface loopback interface-number | N/A |
3. Set the interface description. | description text | The default setting is interface name Interface (for example, LoopBack1 Interface). |
4. Configure the expected bandwidth of the loopback interface. | bandwidth bandwidth-value | By default, the expected bandwidth of a loopback interface is 0 kbps. |
5. Restore the default settings for the loopback interface. | default | N/A |
6. Bring up the loopback interface. | undo shutdown | By default, a loopback interface is up. |