3 Things You Wanted To Know But Never Asked About MAC Addresses

If you’ve ever looked at the details on your network card, you might have noticed an awkward-looking series of alphanumeric characters, separated by either semicolons or a space in a two-by-two fashion. Next to it is either the label “MAC,” “MAC Address,” or “Hardware Address.” As you gaze upon this sequence of characters, a question may pop up in your head: “What in the name of Torvalds is a MAC address?!” And the answer, fellow travelers, is below.

“MAC” is short for “media access control,” and it is used when talking about unique addresses that identify the hardware we use to connect to the internet. In most people’s cases, this is a network interface controller (NIC).

mac addresses nic

But not everyone uses an NIC to connect to the internet. Some people use internal WAN adapters to make wireless connections (through Wi-Fi). These, too, have MAC addresses. Basically, anything connected to the web by any means is identified with a MAC address. And much like your passport number, it’s unique (at least in your own personal network). At the time each device or network card is manufactured, the manufacturer brands the hardware with the address, which is stored in an on-board chip.

That’s the big question, isn’t it? A MAC address sounds like a superfluous thing to have the moment you already have IP addresses. And, in many cases, you are right. However, your home and/or business networks use MAC addresses to communicate internally. This is sometimes superseded by IP communications, but you’re relatively relying on MAC addresses when communicating through the Ethernet layer. It may not always be the case, as technological advances are making MAC-based communication look silly.

For some internet service providers (ISPs), MAC addresses present a really easy way to authenticate computers to give them access to the internet. These ISPs don’t require fancy modems, but do require that your computer’s network card (or your router) have a certain MAC address to gain access to the internet. This was the case with an ISP I used 2 years ago, and it tied a static IP permanently to my computer’s MAC address. There are some disadvantages to having a static IP if you’re a home user, but it works very harmoniously when you host four websites and don’t want to reconfigure everything every time your IP changes.

In short, MAC addresses are chiefly used for two things: internal network communication and external network authentication (on some ISPs).

Although it really isn’t necessary – in most cases – to change your MAC address, most modern network cards and routers have this feature. Their default MAC addresses, however, are often inscribed on them.

mac addresses - nic address

In Windows 7, the process of changing your MAC address is relatively easy:

  • Click on your “Start” menu and then click on “Network.”
  • Click “Network and Sharing Center” near the top of the window.
  • Click “Change adapter settings” on the left-hand side.
  • Right-click on the network adapter you’d like to change the MAC address of and click “Properties.”
  • Click the “Configure…” button.
  • Click the “Advanced” tab.
  • Select “Network Address.”

A text box will show up on the right-hand side of the dialog, labeled “Value.” Select the radio button next to it and type in whatever you want. When you select “Not Present,” you revert the value to the default manufacturer-defined address.

If you still have questions about your MAC address, leave a comment with your question. We have lots of smart readers and authors here who are always handy with these topics!

15 comments

  1. As it is said that MAC address uniquely identify a PC in same networks.
    Now Suppose if I have changed the MAC address of my PC having Window 7 OS with same MAC address of my friend who is also in the same networks then will I be able to change the MAC address. If yes then how my PC or my friend’s PC will be uniquely identified.

    • It won’t be. In fact, I can’t think of any reason you’d want to tinker with a device’s MAC address, except maybe for some advanced debugging. Just seems like asking for trouble.

      • Also, when MAC authentication is present, sometimes your ISP gives you a MAC address that must be configured. In such a case, it is imperative to change it.

    • Maybe just a bit picky but the MAC address deosmn’t identify your PC. It identifies the network card you’re lokking at. If you happen to have 2 card in your PC you will see 2 addresses.
      Just look att the result if you run ipconfig /all on a windows laptop with a LAN card, and a WiFi card. You will see 2 addresses.

  2. It might have been clearer if you’d explained that a MAC address is specific to Ethernet, which is just one type of physical network that is capable of supporting IP (Internet Protocol) communication. There are proprietary networks that run on Ethernet cabling and hardware, but do not use IP to exchange messages. Devices on such a network have MAC addresses, but don’t have IP addresses.

    • The MAC address is NOT specific to Ethernet but can also be used for IP. If you are using IPv6 as opposed to IPv4, your IP Address includes your MAC address BY DEFAULT (although you can override this for purposes of not being tracked).

      • Of the 128 bits within the IPv6 string, the last 64 represent the interface’s identifier. It is determined by one of four methods:

        1) Using the MAC address in its EUI-64 format (like you mentioned)
        2) From a DHCP server that supports IPv6 (great for security, and essential for ISPs operating on IPv6)
        3) Randomization (less common at this point, as #2 might be more feasible for routing purposes)
        4) Manual configuration (most likely to be used in the case of large-scale LANs)

        This is of course in the case of unicast.

      • MAC address are specific to Etherenet frames. IPv4 and IPv6 are just logical routable addresses that is used to identify network and node in network. So IPv4/IPv6 are transported as data inside a Ehternet frame.

        As also noted, the MAC address are used to calculate a Link Local IPv6 address and that can also be used for a Global IPv6 address, but that isn’t needed to be. The Global address node part (usually the lower 64 bit) can be nearly anything you want, even randomized data.

        Ethernet uses frames to transfer data between two computers (yes, a router is a computer too) in the same LAN. That frame contains a couple of things. A preamble (with SFD), destination and source MAC addresses, optional 802.1Q VLAN tag, type/lenght of data (type like IPv4, IPv6, Appletalk etc), the data to be transfered ( usually 46-1500 bytes) and a checksum. But the actual contents can be a bit different, depending on which standard you uses.

        http://en.wikipedia.org/wiki/Ethernet_frame
        http://wiki.wireshark.org/Ethernet

  3. I found a great need to change one computer (bought used) on my network. That computer is one of 5 and the only one that could not contact a certain site. Turns out the site is hosted on a service that subscribes to a “Black List Service”. The MAC address evidently got recorded as a spammer and blocked from accessing any of their customer sites. Changed the MAC problem went away.

    • Sounds strange, as the MAC address doesn’t need to be transfered outside your LAN.
      So ordinary http doesn’t send your MAC address. But as stated, if you use IPv6 then the MAC address could be used to generate a Global IPv6 address. But that could be set to generate a new IPv6 address now and then. So sites should not be able to use your IPv6 address to track you.

    • Yes. Manufacturers produce duplicates sometimes. This has been a problem when people have tried to use two computers within one local network with the same MAC address on their NICs. This is usually an unhappy coincidence and can be rectified using the method described in this article.

      • Yes. And when they have the same MAC address, the computer get strange behaviour when running at the same time. With lots of package loss and confused computers. :-)

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