22
Configuring loopback, null, and inloopback
interfaces
This chapter describes how to configure a loopback interface, a null interface, and an inloopback
interface.
Configuring a loopback interface
A loopback interface is a virtual interface. The physical layer state of a loopback interface is always up
unless the loopback interface is manually shut down. Because of this benefit, loopback interfaces are
widely used in the following scenarios:
•
Configuring 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 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
route from the loopback interface to the peer is reachable by performing routing configuration.
All data packets sent to the loopback interface are considered packets sent to the device itself,
so the device does not forward these packets.
•
Using a loopback interface in dynamic routing protocols
—With no router ID configured for a
dynamic routing protocol, the system selects the highest loopback interface IP address as the router
ID. In BGP, to avoid interruption of BGP sessions due to physical port failure, you can use a
loopback interface as the source interface of BGP packets.
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
3.
Set the interface description.
description
text
The default setting is
interface name
Interface
(for example,
LoopBack1
Interface
).
4.
Configure the expected
bandwidth of the loopback
interface.
bandwidth
bandwidth-value
By default, the expected bandwidth
of a loopback interface is 0 kbps.
5.
Restore the default settings for
the loopback interface.
default
N/A
6.
Bring up the loopback
interface.
undo shutdown
By default, a loopback interface is up.
