The hardware address of an Ethernet card. These are 6 bytes long (eg: 00:00:0C:1A:4B:C3).

You have to 'reserve' part of the MAC address space when you make a network card, so everyone has a unique address. Since everyone's network card is unique, this is often used as a unique identifier for a machine (even though a machine may have multiple network cards, or not have one at all).

An Ethernet packet header contains the source and destination Ethernet MACAddress?es and a Protocol (or Length) field.

You can find out the MACAddress? of your network cards using the ifconfig(8) utility. For example in Linux

$ /sbin/ifconfig eth0 Link encap:Ethernet HWaddr 00:07:A9:11:40:A8 ...

It may look different in other Unix variants, OpenBSD shows the following

$ /sbin/ifconfig -a rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500

address: 00:05:1d:9b:f1:10

CategoryNetworking