F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices Network Management Configuration Guide-6PW100

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378BConfiguring a loopback interface
1078BIntroduction
A loopback interface is a virtual interface. The physical layer state and link layer protocols of a loopback
interface are always up unless the loopback interface is manually shut down. A loopback interface is
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.
1079BConfiguration procedure
To configure a loopback interface:
Ste
p
Command Remarks
53. Enter system view.
system-view
N/A
54. Create a loopback interface and
enter loopback interface view.
interface loopback
interface-number
N/A
55. Set the interface description.
description text
Optional.
By default, the description of a loopback
interface is interface name Interface.
56. Shut down the loopback interface.
shutdown
Optional.
By default, a loopback interface is up.
57. Restore the default settings for the
loopback interface.
default Optional.
You can configure settings such as IP addresses and IP routes on loopback interfaces.
379BConfiguring the null interface
1080BIntroduction
A null interface is a completely software-based logical interface, and is always up. However, you cannot
use it to forward data packets or configure an IP address or link layer protocol on it. With a null interface
specified as the next hop of a static route to a specific network segment, any packets routed to the
network segment are dropped. The null interface provides a simpler way to filter packets than ACL. You
can filter uninteresting traffic by transmitting it to a null interface instead of applying an ACL.