Mastering Proxmox - Third Edition

Bridge ports

The Bridge ports textbox is to type in the physical network interface of the host to which this bridge will be connected. There is no drop-down menu to choose a physical network interface from. The name of the interface needs to be typed in. If the virtual network traffic is not going to go out of the node but will remain isolated among the virtual machines within the node, then we can leave the port's textbox blank. 

It is important to note here that we can only configure one virtual bridge per physical network interface. One physical interface can never be shared among multiple bridges.