H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 23)

14
Loopback and null interface configuration
This chapter includes these sections:
• Configuring a loopback interface
• Configuring the null interface
• Displaying and maintaining loopback and null interfaces
NOTE:
•
The term "switch" or "device" in this chapter refers to the switching engine on a WX3000E wireless
switch.
• The WX3000E series comprises WX3024E and WX3010E wireless switches.
• The port numbers in this chapter are for illustration only.
Configuring a loopback interface
Introduction to the loopback interface
A loopback interface is a software-only virtual interface. It delivers the following benefits.
• The physical layer state and link layer protocols of a loopback interface are always up unless the
loopback interface is manually shut down.
• You can assign a loopback interface an IP address with an all-F mask to save the IP address
resources. When you assign an IPv4 address whose mask is not 32-bit, the system automatically
changes the mask into a 32-bit mask. When you assign an IPv6 address whose mask is not 128-bit,
the system automatically changes the mask into a 128-bit mask.
• You can enable routing protocols on a loopback interface, and a loopback interface can send and
receive routing protocol packets.
Because of the benefits mentioned above, loopback interfaces are 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. Therefore, when you configure a rule on an authentication or security server to
permit or deny packets generated by a device, you can simplify the rule by configuring it to permit or
deny packets carrying the loopback interface address identifying the device. Note that, when you use a
loopback interface address as the source address of IP packets, make sure that 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 as packets sent to the device itself, so the device does not forward
these packets.
Configuration procedure
Follow these steps to configure a loopback interface: