MAC Address Basics

Each of a hosts network interfaces has a link layer MAC address that distinguishes it from other machines on the physical network. IP addresses are assigned to network interfaces and not machines. A mac address is made up of 48 bits or 6 bytes and is split into two parts. The first 3 bytes identify the manufacturer and the last 3 bytes are a unique serial number, so in this example the green sections are the vendor id and the black section is the interfaces unique number 32-03-C8-73-DC-A1. This is important for network engineers in spotting devices or vendors that are causing havoc on the network. 

Broadcasting

Broadcasting is a send once to all method of communication. A MAC address needs to be assigned to a broadcast frame. This address is made up of all binary 1s and when converted to hexadecimal gives you FF:FF:FF:FF:FF:FF

Multicasting

Multicasting works similar to broadcasting, but instead of sending data to all it sends it to a targeted group, often called one to many transmission. Common applications that use multicasting are streaming channels like Twitch and Youtube live. To avoid collisions when an ethernet switch receives a multicast frame it floods it out of all ports except the incoming port.

MAC address tabling

A switch stores mac addresses in a table. This table is called a mac address table or a content addressable memory (CAM table).  A switch stores information about other ethernet interfaces which are connected on the network. When a switch receives a frame it correlates the device sending with interface where it was received. 

A MAC address table maps each and every port to a MAC address and it does this in two ways;

Static - Have higher priority than dynamic as they can be added, removed or changed by an administrator

Dynamic - Added to the table automatically by a process called MAC learning. Once a switch receives a frame it automatically updates it mac address information. There is a brief video below showing how a mac address table works in practice.