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Possible Duplicate:
Is your MAC address revealed when you hit up a website?

Can anybody see my MAC address when I'm on the Internet?

Also, where can I check my MAC address?

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Carol
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  • Which MAC? The most exposed one should just be your Modem (or whatever connects you to your ISP). Your computer is removed by a step or two typically (Modem --> Router --> Computer) – nerdwaller Nov 26 '12 at 18:30

2 Answers2

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The MAC-address is part of the Link-Layer in the OSI Network Model. I wont go too deep in here, bottom line is, it's only used for communication in your local network, be it cabled or wireless.
The point at which your computers MAC definitely gets lost is when it passes your router, the router only transmits the IP packet to "the Internet". When connecting to the internet your router will not use your computers, but its own MAC address to forward the packet.
This switcheroo happens on all routing points, so your ISP will take your packet, get the IP packet out and put it into another MAC packet and so on.

However, if you are using IPv6 it might be possible that your IP Address can be generated using parts of your computers MAC address.

The tools to check your MAC (and IP) addresses are different from system to system, note they only show your computers local addresses, not what can be seen on the Internet.
Not sure about Windows, I think it's ipconfig /all
For Linux (and OSX) it's ifconfig

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Baarn
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Nobody can see your MAC address on the Internet. Only people on the same LAN as you can see your MAC address. (That sometimes includes people sharing WiFi with you.)

David Schwartz
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  • People don't necessarily have to share the WiFi, MAC addresses sent wireless are always visible, as long as in range of course. – Baarn Nov 26 '12 at 18:42
  • @Informaficker - Actually they do have to transmit it. – Ramhound Nov 26 '12 at 18:48
  • no MAC no communications – Fiasco Labs Nov 26 '12 at 19:19
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    @FiascoLabs that's not true, there is MAC-less communication, although it is not very common afaik. – Baarn Nov 28 '12 at 21:53
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    @Informaficker - Explain that please. IP addressing depends on ARP to match an IP to a MAC address. – Fiasco Labs Nov 30 '12 at 16:39
  • @FiascoLabs I though there were some devices that did not rely on MAC for IP transfer, as it isn't really needed on a single link connection, but I have not found anything regarding that matter. I am removing this part from my answer. – Baarn Nov 30 '12 at 19:58
  • @FiascoLabs That is only true on network protocols that use MAC addresses such as Ethernet and WiFi. There are lots of other ways to exchange IP traffic. – David Schwartz Nov 18 '20 at 05:20