H3C Technologies H3C WX5500E Series Access Controllers - Manual (Page 27)

16
Configuring loopback and null interfaces
This section describes how to configure loopback and null interfaces.
Configuring a loopback interface
A loopback interface is a virtual interface. The physical layer state and link layer protocols of a loopback
interface are always up unless the loopback interface is manually shut down. A loopback interface is
widely used in the following scenarios:
• You can configure 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 that the
peer is reachable through routes by performing routing configuration. All data packets sent to the
loopback interface are considered as packets sent to the device itself, so the device does not
forward these packets.
• You can use a loopback interface in dynamic routing protocols. For example, if no router ID is
configured for a dynamic routing protocol, the highest loopback interface IP address is selected as
the router ID.
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
Optional.
By default, the description of a
loopback interface is interface name
Interface.
4. Shut down the loopback
interface.
shutdown
Optional.
By default, a loopback interface is up.
5. Restore the default settings for
the loopback interface.
default Optional.
You can configure settings such as IP addresses and IP routes on loopback interfaces. For more
information, see Layer 3—IP Services Configuration Guide and Layer 3—IP Routing Configuration
Guide.