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Does my MAC address list my name, ect? How do I find out exactly what the MAC address tells me? I know it's the "physical address" of my laptop, but what exactly does that mean? This is what my MAC address says:

00-26-6c-44-4d-00  Media Disconnected
B4-82-FE-06-96-C0  /DEVICE/TCPIP_{5DFCF8F8-49A7-46BB-BD91-85F9D0606E98}
B4-82-FE-06-96-C0  Media Disconnected

I'm clueless and concerned about this for tracking purposes.

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Related: superuser.com/questions/114110/… –  Sathya Sep 11 '10 at 15:48

3 Answers 3

From wikipedia's MAC address :

A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model.

MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number. It may also be known as an Ethernet hardware address (EHA), hardware address, adapter address, or physical address.

Although intended to be a permanent and globally unique identification, it is possible to change the MAC address on most of today's hardware, an action often referred to as MAC spoofing. Unlike IP address spoofing, where a sender spoofing their address in a request tricks the other party into sending the response elsewhere, in MAC address spoofing, the response is received by the spoofing party. However, MAC address spoofing is limited to the local broadcast domain.

In the IPv4 world, the MAC address of your computers is not propagated or detectable beyond your local network. This means that under normal browser operation (without plugin intervention), the MAC address of any computer positioned behind the router is not sent beyond the router, and so cannot be used to track you over the Internet. However, the router uses it internally in order to identify the local computers.

In IPv6, the 64 bit "host" part of the full 128 bit address is often automatically generated from the MAC address, and hence often is visible to the server one connects to. This means that outsiders may trace the MAC address of your router and your Internet-connected computers. IPv6 gives a public, routable address to every last PC, server, printer or network device (unless the router does NAT processing, which is rare in IPv6).

If Private IPv6 addresses (defined in RFC 4941) is turned on, the exposed identifier is generated as a random number rather than from the MAC. This is the default on many operating systems, but can be turned on and off. For further info see How to avoid exposing my MAC address when using IPv6.

In any case, your ISP always knows who you are and can trace anything you do, unless the traffic is encrypted by using a VPN.

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That is much easier to understand, thank you. So for instance, if I visited a website over a public network connection using my WiFi Laptop, my MAC address would not reveal my name or address or other information used when I registered or bought the computer? Thank you so much again! –  Marie Sep 11 '10 at 15:51
    
That is correct: The website can't find out the MAC address. However, the public network router does know it and may even log all your Internet requests, unless you also use a VPN or proxy. –  harrymc Sep 11 '10 at 15:55
    
@harry, I don't think packets carry MAC over http/ftp so the DSL/cable modem is the last thing to "see" it. –  hyperslug Sep 11 '10 at 17:38
    
@hyperslug: Not for ftp/http, but to connect to the router. –  harrymc Sep 11 '10 at 17:48
    
As an aside, to get the MAC address from the last 64 bits of an IPv6 address: strip the ff-fe part from the middle, and complement the second low-order bit of the first byte (if the bit is a 1, make it 0, and if it is a 0, make it 1). For example, for 0060:08ff:fe52:f9d8, the first byte 0x00 (00000000) becomes 0x02 (00000010). Therefore, 0060:08ff:fe52:f9d8 in an IPv6 address translates back to MAC address 02:60:08:52:f9:d8. –  Arjan Feb 4 '11 at 11:56

MAC addresses are written in the form AA-BB-CC-DD-DD-FF. The first 3 numbers (i.e. AA-BB-CC) identify a manufacturer, e.g.:

00-26-6C-xx-xx-xx   Inventec
B4-82-FE-xx-xx-xx   Askey Computer Corp

On the other hand, each MAC address is unique to every network card on earth. So it is a number uniquely assigned to you.

But nobody can link a MAC address to you.

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Well...we can now. =) –  hyperslug Sep 11 '10 at 15:59
    
Good luck finding him. –  Ian Boyd Sep 12 '10 at 0:57
    
+1 for directly answering the question, rather than just explaining what a MAC address is. –  Scott Feb 3 '11 at 16:41

Every network interface card (NIC) is assigned from the factory a media access control address, or MAC address. In most cases, the MAC address on a network card does not change, so essentially the address identifies the physical piece of hardware. MAC addresses are necessary for routing data across networks. They don't contain user-identifiable information, and usually they aren't even visible outside of your local network.

Looking at the data you've posted, your computer appears to have two network interfaces defined, probably a wired Ethernet port and a wi-fi connection. Only one of those interfaces (with address B4-82-FE-06-96-C0) has an active network attached to it. The "/DEVICE/TCPIP..." bit is just how Windows keeps track of your network interfaces.

There is a comprehensive description of MAC addresses on Wikipedia.

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Thank you so much for all the great (and easy to comprehend) advice. I believe I may have been the victim of attempted identity theft via PayPal. (someone applied for a credit card in my name.) The police has told me that he can obtain records about exactly who (by name) what (type of computer) and where (exact address of the person who did it) It seems this would only be possible if the person I think did this handed over their computer, which is unlikely. it seems that this is not aviable option of finding out who did it. If I'm wrong, please let me know. –  Marie Sep 11 '10 at 16:07
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In this case the police may be able to find out (from PayPal) the public ip-address the request came from. That address is provided (usually) by an ISP and they can be asked to check their records to find out what device they gave it to - that will usually be a DSL\cable modem but that has an identity too - and a MAC address for what that's worth. The ISP will be able to associate it with an account too - in many cases that will be who they are looking for but if it leads to a public Internet service \ WiFi zone it will require further digging. –  Helvick Sep 11 '10 at 16:48
    
All this may require several court-orders as well ... –  harrymc Sep 11 '10 at 17:05

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