Linux in a Nutshell, 6th Edition

Network Concepts

For your virtual server to connect to the Internet it must have a way to use the physical connection of the host. Xen, KVM, and VMware will all create a default bridge interface to handle mapping the virtual systems to the physical interface. A virtual machine could also be assigned directly to a physical device, but for most situations a bridge is what you want. More complex network configurations can be made by defining a kind of virtual switch or router. We will cover some commands that can do this here.