In Computer networking, the MAC (Media Access Control) address is every bit as important as an IP address. You will learn in this article how MAC addresses work and how to find the MAC addresses being used by a computer.
First, What is MAC Address?
The MAC address is a unique value associated with a network adapter. MAC addresses also known as hardware addresses or physical addresses. They uniquely identify an adapter on a LAN (Local Network Address).
MAC addresses are 12 digit hexadecimal numbers (48bits in length). By convention, MAC addresses are usually written in one of the following two formats:
1- MM:MM:MM:SS:SS:SS
2- MM-MM-MM-SS-SS-SS
The first half of a MAC address contains the ID number of the adapter manufacturer. These IDs are regulated by an Internet standard body. The second half of a MAC address represents the serial number assigned to the adapter by the manufacturer.
In the example, 00:A0:C9:14:C8:29
The prefix 00A0c9
indicates the manufacturer is Intel Corporation
More about MAC address:
The TCP/IP and other mainstream networking architectures generally adopt the OSI model. In this model, network functionality is subdivided into layers. MAC addresses function at the data link layer (which layer 2 is the OSI model). They allow computers to uniquely identify themselves on a network at this relatively low level.
IP Addressing vs MAC
IP addressing functions at the network layer (which is layer 3) and MAC addressing works at the data link layer. It is a slight over simplification, but one can think of IP addressing as supporting the software implementation and MAC addresses as supporting the hardware implementation of the network stack. The MAC address generally remains fixed and follows the network device, but the IP addres changes as the network device moves from one network to another.
IP networks maintain a mapping between the IP address of a device and its MAC address. This mapping is known as the ARP cache or ARP table.
ARP = Address Resolution Protocol, supports the logic for obtaining this mapping and keeping the cache up to date.
DHCP also usually relies on MAC addreses to manage the unique assignment of IP addresses to devices.
Method Use in finding MAC address
The method used to find a MAC address depends on the type of network device involved. All popular network operating systems contain utility programs that allow you to find MAC address settings and it change sometimes.
Finding MAC address in Windows
Use the ipconfig utility (with the/all option) to display the computer’s MAC address in modern versions of windows. Very old versions like Windows 95 and Windows 98 used the winipcfg utility instead.
Both “winipcfg” and “ipconfig” may display multiple MAC addresses for one computer. One MAC address exists for each installed network card.
Additionally, Windows maintains one or more MAC addreses that are not associated with hardware cards.
Example, Windows dial-up networking uses virtual MAC addresses to manage the phone connection as if it were a network card. Some windows VPN clients likewise have their own MAC address. The MAC addresses of these virtual network adapters are the same length and format as true hardware addresses.
Finding MAC address in UNIX or LINUX
The specific command used in Unix to find a MAC address varies depending on the version of the operating system. In Linux and in some forms of Unix, the command is ifconfig -a returns MAC addresses.
You can also find MAC addresses in Unix and Linux in the boot message sequence, these operating systems display the computer’s MAC address on screen as the system reboot. Boot up messages are retained in a log file, it is usually “/var/log/messages” or “/var/adm/messages”.
Finding MAC address on the Apple Mac
You can find MAC addresses on Apple Mac computers in the TCP/IP control panel. If the system is running Open transport, the MAC addres appears under the “info” or “user mode/advanced” screens. If the system is running macTCP, the MAC address appears under the “Ethernet” icon.
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