Configuring A Loopback Interface; Null Interface; Introduction To Null Interface; Configuring A Null Interface - 3Com MSR 50 Series Configuration Manual

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HAPTER OGICAL
Configuring a Loopback
Interface

Null Interface

Introduction to Null
Interface
Configuring a Null
Interface
I C
NTERFACE ONFIGURATION
authentication server/security server to permit/deny packets with a specific
loopback interface address as their source IP addresses can permit/deny all the
packets sourced from the corresponding device. In this way, the packet filtering
rules are simplified. Note that, when a loopback interface is used for source
address binding, you need to make sure that the route from the loopback
interface to the peer is reachable. In this case, all the data packets destined for the
loopback interface are sent to the device itself, and the device does not forward
these packets.
Because a loopback interface is always up, it can be used for some special
purposes. For example, if the router ID of a device is not available, some dynamic
routing protocol uses the highest loopback interface address of the device as the
router ID.
Table 21 Configure a loopback interface
Operation
Enter system view
Create a Loopback interface
and enter Loopback interface
view
Shut down a loopback
interface manually
c
CAUTION:
Only 32-bit subnet masks can be configured for Loopback interfaces.
■
Parameters such as IP addresses and IP routes can be configured on Loopback
■
interfaces. Refer to
configurations.
Null interfaces are completely software-like logical interfaces. Null interfaces are
always up. However, they can neither forward data packets nor have IP addresses
or link layer protocols configured on them. 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. If you configure to send unwanted traffic to the
null interface of a device, the unwanted traffic will be filtered. In this way,
complicated ACL configurations are saved.
For example, the static route configuration command ip route-static 92.101.0.0
255.255.0.0 null 0 will have all the packets destined to the network segment
92.101.0.0/16 discarded.
Table 22 Configure a null interface
Operation
Enter system view
Command
system-view
interface loopback
number
shutdown
"IP Addressing Configuration" on page 623
Command Description
system-view -
Description
-
-
Optional
Always in the up state by default
for detailed