Bridges

Overview

A bridge refers to the IEEE 802.1d set of standards. It is a networking device that creates a single, aggregate network from multiple different networks or network segments.

Switches

A switch is a networking device that connects multiple devices together. Multiple data cables are plugged into a switch to enable communication between different networked devices.

A switch is more intelligent than an Ethernet hub, which retransmits packets out of every hub except the port on which the packet was received.

Filtering Databases

As a network transmits traffice, bridges "learn" which port MAC addresses are available on. These lists are stored in tables called filtering databases (within each switch on a per-port (and possibly per-VLAN) basis. Filtering databases are called forwarding databases (FDBS) in Linux parlance.

If a filtering database entry does not exist for a given MAC address, the bridge is forced to send the frame on every port. This is called flooding.