D-Link DI-1750 Reference Manual page 33

The null interface can be used in any command that has an interface type as an argument. The
following example configures a null interface for IP route 192.168.20.0.
ip route 192.168.20.0 255.255.255.0 null 0
2. Configure a Loopback Interface
A loopback interface is a logical interface that is always up and allows BGP sessions to stay up even if
the outbound interface is down. You can use the loopback interface as the termination address for BGP
sessions. In applications where other routers or access servers attempt to reach this loopback interface,
you should configure a routing protocol to distribute the subnet assigned to the loopback address.
Packets routed to the loopback interface are rerouted back to the router and processed locally. IP
packets routed out the loopback interface but not destined to the loopback interface are dropped. This
means that the loopback interface serves as the Null interface also.
To specify a loopback interface and enter interface configuration mode, use one of the following
commands in global configuration mode:
Command
interface
loopback number
Input the command "interface", it will prompt:
(00)FastEthernet
......
(05)Loopback
.....
Please Input the code of command to be excute(0-10): 5
Input 5，choose the item "Loopback", it will prompt:
Please input a interface name:
Input the "loopback interface".
3. Configure Dialup Interface
The dialup interface is a kind of logical interface, which configure the dialup setting of multiple physical
interfaces in one virtual interface. Thereby, the dialup interface will builds the communication of
physical interface and dialup interface to manage multiple interfaces in the same time.
Use following command to configure dialup interface:
interface dialer number
dialer rotary-group number
Command 1:
Input the command "interface" in global configurative mode, it will prompt:
(00)FastEthernet
......
(07)Dialer
.....
Please Input the code of command to be excute(0-10): 7
Input 7, choose the item "Dialer", it will prompt:
Please input a interface name:
Input the dialer number.
Command 2：
Set the interface to dial-up, choose the item "Dialer" of prompt, it will display:
(00)called
Enter the status of loop-back interface configuring
FastEthernet interface
Loopback interface
Command
FastEthernet interface
Dialer interface
Dialer called string
Model Name
Function
Function
Enter the status of dialup interface configuring
Set the communication of dialup interface and physical
interface
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