HP A5120 EI Series Configuration Guide

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

HP A5120 EI Series Specifications

General

Uplink Ports	4 x SFP
Stacking	No
Management	CLI, Web, SNMP
Routing Protocols	RIP, OSPF
Power Supply	AC
MAC Address Table Size	16K
Dimensions	440 x 430 x 44 mm
Operating Temperature	0°C to 45°C
Operating Humidity	10% to 90% non-condensing
Model	HP A5120-24G EI Switch (JG234A)
VLANs	4094