The virtual machine running the operating system is called a domain. The host OS, called Domain-0, is booted at system startup.
The interface, called ethX, is created so Domain-0 can access communications, and the interface vif0.X for connecting Domain-0's ethX and the server as well as the interface path for external connections are created. These are created for each NIC on the server. In addition, the virtual bridge called xenbrX is created to connect vif0.X and pethX for external connections.
When you create a new guest domain (domain U) and boot the operating system, the interface vifU.X for connecting domain U's ethX and the server is created. In addition, vifU.X and the interface pethX for external connections are connected by the virtual bridge, enabling ethX on the guest domain to connect to the outside network.
If you use the tagged VLAN, a virtual bridge named gextbrX is created. Additionally, an interface pethX.Z (Z is an ID for the tagged VLAN) will be created for sending VLAN-tagged packets outside the server and untagging them when received.
