A network bridge is nothing but a Linux device that creates a single aggregate network from multiple interfaces or segments. This function named as network bridging, and this post explains how does Linux networking bridge work with examples.
From the blog post:
Linux bridge is a layer 2 virtual device that on its own cannot receive or transmit anything unless you bind one or more real devices to it. source.
As Anatomy of a Linux bridge puts it, bridge mainly consists of four major components:
Set of network ports (or interfaces): used to forward traffic between end switches to other hosts in the network.
A control plane: used to run Spanning Tree Protocol (STP) that calculates minimum spanning tree, preventing loops from crashing the network.
A forwarding plane: used to process incoming input frames from the ports, forward them to the network port by making a forwarding decision based on the MAC learning database.
MAC learning database: used to keep track of the host locations in the LAN.
- Read more: Linux Bridge – how it works