The Linux bridge

The Linux bridge is a software layer 2 device that provides some of the functionality of a physical bridge device. It can forward frames between KVM guests, the host OS, and virtual machines running on other servers, or networks. The Linux bridge consists of two components--a userspace administration tool that we are going to use in this recipe and a kernel module that performs all the work of connecting multiple Ethernet segments together. Each software bridge we create can have a number of ports attached to it, where network traffic is forwarded to and from. When creating KVM instances, we can attach the virtual interfaces that are associated with them to the bridge, which is similar to plugging a network cable from a physical server's NIC to a bridge/switch device. Being a layer 2 device, the Linux bridge works with MAC addresses and maintains a kernel structure to keep track of ports and associated MAC addresses in the form of a Content Addressable Memory (CAM) table...