Loopback And Null Interface Configuration; Loopback Interface; Introduction To Loopback Interface; Configuring A Loopback Interface - HP A5120 EI Series Configuration Manual

Loopback and null interface configuration

Loopback interface

Introduction to 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.
To save IP address resources, you can assign an IP address with an all-F mask to a loopback

interface. 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.
You can configure a loopback interface address as the source address of the IP packets that the switch
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 switch generates, you can simplify the rule by configuring it to permit or deny packets
that carry the loopback interface address that identifies the switch. When you use a loopback interface
address as the source address of IP packets, be sure to perform any necessary routing configuration to
ensure that the route from the loopback interface to the peer is reachable. All data packets sent to the
loopback interface are treated as packets sent to the switch itself, so the switch does not forward these
packets.

Configuring a loopback interface

Follow these steps to configure a loopback interface:
To do...
Enter system view
Create a loopback interface and
enter loopback interface view
Set a description for the loopback
interface
Shut down the loopback interface
Use the command...
system-view
interface loopback interface-
number
description text
shutdown
17
Remarks
—
—
Optional
By default, the description of an
interface is the interface name
followed by the ―Interface‖ string.
Optional
By default, a loopback interface is
up after it is created.