Configuring The Loopback And Null Interface; Configuring A Loopback Interface - HP A5830 Configuration Manual

Configuring the loopback and null 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 shut down manually.
 To save IP address resources, 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.
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.
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 generated by a device, simplify the rule by configuring it to permit or deny packets
that carry the loopback interface address identifying the device. When you use a loopback interface
address as the source address of IP packets, perform any necessary routing configuration to make
sure 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 device itself, so the device does not forward
these packets.
Because a loopback interface is always up, use it in dynamic routing protocols. For example, if you

do not configure a router ID for a dynamic routing protocol, the highest loopback interface IP
address is selected as the router ID. In BGP, to prevent physical port failure from interrupting BGP
sessions, use a loopback interface as the source interface of BGP packets.

Configuring a loopback interface

To configure a loopback interface:
Step...
1. Enter system view
2. Create a loopback interface
and enter loopback interface
view
3. Set the interface description
4. Shut down the loopback
interface
5. Restore the default settings for
the loopback interface
Command...
system-view
interface loopback
interface-number
description text
shutdown
default
14
Remarks
—
—
Optional
By default, the description of a loopback
interface is interface name Interface
Optional
By default, a loopback interface is up
Optional