How Bridges Work

Bridges are physical devices that have the ability to increase the throughput of a LAN by filtering frames between LAN segments based on hardware addresses or MAC addresses. Bridges work up to the Data-Link Layer.   A MAC (Media Access Control) address is an address that is unique to each physical network card. The MAC address is burned into the network card to give it a unique identifier. MAC addresses only identify the network card they have nothing to do with identifying a network. Each MAC address is made up of a 48-bit hexadecimal number. This number is created in two-digit numbers separated by a colon. The first 24 bits represent the code assigned by the IEEE to identify the manufacturer of the network card. The last 24 bits represent a number that identifies the network card.

Lesson 4 / Lesson 6

At the Data-Link Layer, the signals are organized into frames called Media Access Control (MAC) frames. The frame headers contain source and destination addresses of NICS, the physical address.