Double click the element to which you will add a virtual interface.
The Configure dialog box appears.
Click the + button in the Virtual Interfaces area of the screen.
A virtual port is added to the element such as eth0:1 or eth1:1.
You may add up to 16 virtual ports per physical (real) port.
Click OK/Apply.
The Configure screen is closed.
Choose Save from the File menu.
The virtual port configuration is saved.