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Loopback Interface and Null Interface
Configuration
When configuring loopback interfaces and null interfaces, go to these sections for information you are
interested in:
z
Loopback Interface
z
Null Interface
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Displaying and Maintaining Loopback and Null Interfaces
Loopback Interface
Introduction to Loopback Interface
A loopback interface is a software-only 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 can be configured with an IP address. For the purpose of saving IP address
resources, the IP address is automatically configured with a 32-bit mask. Routing protocols can be
enabled on a loopback interface, and a loopback interface is capable of sending and receiving routing
protocol packets.
Loopback interfaces are widely used. For example, you can configure a loopback interface address as
the source address of all the IP packets that the device generates. Because loopback interface
addresses are stable unicast addresses, they are usually used as device identifications. Therefore,
when you configure a rule on an authentication or security server to permit or deny packets generated
by a device, you can streamline the rule by configuring it to permit or deny packets carrying the
loopback interface address identifying the device. Note that, when a loopback interface is used for
source address binding (that is, assigning an IP address to this loopback interface), make sure that
the route from the loopback interface to the peer is reachable; 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.
Because a loopback interface is always up, it can be used for some other special purposes. 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. For another example, to avoid BGP sessions being interrupted by
physical port failure, you can use a loopback interface as the source interface of BGP packets.
However, you must ensure that the IP address of the loopback interface on the BGP peer is reachable.
If EBGP connection is involved, you need to allow the establishment of EBGP connections to
non-directly-connected peers.
Configuring a Loopback Interface
Follow these steps to configure a loopback interface:
To do…
Use the command…
Remarks
Enter system view
system-view
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Содержание S7902E
Страница 82: ...1 4 DeviceA interface tunnel 1 DeviceA Tunnel1 service loopback group 1 ...
Страница 200: ...1 11 DeviceB display vlan dynamic No dynamic vlans exist ...
Страница 494: ...ii Displaying and Maintaining Tunneling Configuration 1 45 Troubleshooting Tunneling Configuration 1 45 ...
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Страница 1757: ...4 9 ...
Страница 1770: ...6 4 ...
Страница 2017: ...2 11 Figure 2 3 SFTP client interface ...
Страница 2062: ...i Table of Contents 1 URPF Configuration 1 1 URPF Overview 1 1 What is URPF 1 1 How URPF Works 1 1 Configuring URPF 1 2 ...
Страница 2238: ...1 16 DeviceA cfd linktrace service instance 1 mep 1001 target mep 4002 ...
Страница 2442: ...2 4 Set the interval for sending Syslog or trap messages to 20 seconds Device mac address information interval 20 ...