H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 20)

10
Configuring loopback and null interfaces
Configuring a loopback interface
Overview
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.
• Loopback interfaces save the IP address resources. When the device is assigned an IPv4 address
mask which is not 32 bits in length, the system automatically changes the length into 32 bits. When
the device is assigned an IPv6 address mask which is not 128 bits in length, 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:
• A loopback interface address can be configured 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
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.
• A loopback interface is often used 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. In BGP, to avoid BGP sessions being interrupted by physical port failure, you can use
a loopback interface as the source interface of BGP packets.
Configuration procedure
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