Finding your MAC

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Your MAC address is a series of hex numbers intended to uniquely identify a network interface device (network card). They can be changed or faked, and this is sometimes useful in routers. They can be useful to control network access, e.g. only allowing certain computers to use a wireless home network or ensuring a printer always gets the same IP address through DHCP.

Each wireless card and LAN card will have its own MAC, usually printed on a label attached to it. There are many ways to find the MAC from device interface dialogues so we will only specify consistent ways for each operating system.

Do not get confused by MAC (migration authorisation code) codes required if you wish to move internet service providers - this MAC is generated and supplied (sometimes reluctantly) by your current ISP and allows for seamless broadband migration to another company. If you just cancel your current ISP and start a new one there can be a delay of weeks before you are online again!

Contents

Windows XP

Illustration of finding your MAC address in Windows XP.
  • start>run>cmd>arp -a
  • start>run>cmd>ipconfig /all will give you more information regarding the network you are on including MAC address (called physical address in the terminal windows that pops up), default gateway,subnet mask, DNS servers and importantly your current IP address. This is the place to start if you are experiencing network problems.

Linux

  • from an xterm or similar session type "ifconfig -a" and for each device with a MAC you will get output with hardware address (HWaddr)...as in italics below

eth0 Link encap:Ethernet HWaddr 00:1B:11:D3:32:E2

Depending on the setup of the system you may need to give the full path in the commandline - /sbin/ifconfig and in some setups such as the SUN Cobalt Raq you may have to be root.

Macintosh OS/X

In the BSD-based Unixes the procedure is the same as in Linux, above.

Routers

  • log into your Web Administration interface. Screens labelled as Router Status / Device Status / Connection Status will quickly allow you to identify MACs for both the router and any successfully connected network interfaces