Adding a virtual network interface using webmin

There are two situations in which you might want to add a new network interface – if your system has just had a network card installed, or if you are adding an additional virtual IP address to an existing interface. In the latter case, the new virtual interface is not associated with its own separate network card, but instead adds an additional IP address to an existing Ethernet card. Virtual addresses are often used on systems hosting multiple websites, so that each site can have its own IP address.

Before an interface for a new network card can be configured, you must make sure that it is recognized by the Linux kernel and the appropriate kernel module loaded. There is no support in Webmin for doing this at the moment, but most distributions include a graphical tool for loading kernel modules, or a configuration file in /etc that specifies which modules to load. Once the interface is recognized, the steps to configure it are :

1. On the main page of the module, click the Add a new interface link under Interfaces Activate at Boot Time. 
2. Enter the interface name (such as eth1 or tr0) into the Name field. This must correspond to whatever name has been assigned by the kernel.
3. In the IP Address field, either enter an address or select the From DHCP option for it to be dynamically assigned.
4. Enter the netmask for the network the interface is on into the Netmask field, such as 255.255.255.0.
5. Set the Broadcast field based on the address and netmask. For example, if the IP was 10.1.2.3 and the netmask was 255.0.0.0 then the broadcast address would be10.255.255.255.
6. If you want the interface to be brought up at boot time, set the Activate at boot? field to Yes.
7. Finally, click the Create button. Assuming there are no errors in your input, you will be returned to the list of interfaces.
8. To make the interface active now, click on its name from the Interfaces Activate at Boot Time list. Then on the editing form, click the Save and Apply button. If any error occurs during activation (such as the interface not being recognized by the kernel) Webmin display an error message.

A virtual interface adds an additional IP address to an existing real interface. Virtual interfaces have names like eth0:1, where eth0 is the name of the real interface and 1 is the virtual number. To add one, the steps to follow are :

1. On the main page of the module, click on the real interface that you want to add a virtual address for, under Interfaces Activate at Boot Time.
2. On the editing form, click the Add virtual interface link. This will take you to a creation form, similar to Figure 16-2.
3. In the Name field, enter a number for the virtual interface. This must not be used by any existing virtual interface on the same real network card.
4. Fill in the IP Address field with the address that you want to assign to the virtual interface.
5. The Netmask and Broadcast fields should be set to the same addresses as the real interface. They would only be different if the virtual interface was on a different IP network that was sharing the same LAN as the network for the real interface.
6. Assuming you want the virtual interface to be created at boot time, set the Activate at boot? field to Yes.
7. Hit the Create button. As long as there are no errors in your input, you will be return to the list of interfaces. Your new virtual interface will appear under its real parent in theInterfaces Activate at Boot Time section.
8. To activate the virtual interface immediately, click on its name and on the editing form click the Save and Apply button.