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I am using dial up connection to connect to the internet. It shows an physical address for that connection.

My OS is Windows XP.

I can change the physical address of a Local area connection and Wireless network connection by modifying the registry values. However I have not been able to change the physical address of my Dial up connection that I use to connect to my ISP. So my question is it possible to change that address? If possible then please suggest a way to change it.
One another point is that I read somewhere that There is no need of physical address between point to point dial up connection, then what this address stands for?

enter image description here


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up vote 4 down vote accepted

Modems in general do not have MAC addresses, instead they have IMEI numbers. It is a point-to-point pipe, so whatever goes in one end is coming out of the other end and is dealt with by the routing protocol at each end.

Changing the MAC of a dial-up is not as weird as it sounds, especially when one has two computers using the same dial-up modem at the same time. Some sophisticated Cisco routers can, under certain conditions, do MAC filtering as described in this old document. However, I really doubt that your dial-up modem has the capability to let you configure its built-in IMEI number.

Windows XP will use by default the fictional address of 00-53-45-00-00-00 for ALL such virtual adapters. Somebody at Microsoft had some fun here, because 53=35(hex) and 53-45=5+3.

This "MAC" address is built into the dial-up software and changing it will require the binary hacking of the involved Windows component. But this will most probably have absolutely no effect on what your ISP will be seeing.

Some MAC Address Changer tools may appear to change this address, for example Win7 MAC Address Changer. But even if it "works", it is probably only a meaningless change on the Windows side, that your ISP will never see.

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Is Win 7 does not have any default fictional address that you mentioned in case of Win XP? because when I run the same command in Win 7 the physical address shows empty. Another question is what an ISP does see to track you? – Deb Aug 14 '12 at 5:06
I haven't used dial-up for many years (since ADSL came out). It may be that in Windows 7 this fictional MAC address is no longer necessary. The modem must transmit to the ISP an identification which must be unique for the entire network, which is usually its IMEI number. That is the only identifying information about you that your ISP will see (except for your message traffic of course). – harrymc Aug 14 '12 at 5:48

Each ethernet interface has an unique, vendor configured 48 bit number so it can be identified on the local network.

You can read more about that on wikipedia. (Wikipedia: Media Access Control)

Many devices allow you to change the MAC. This is something you never need to do unless:

  • You are curious how things work and are playing with the network.
  • You want to immitate an other computer on the local network (e.g. for cracking).
  • The vender gave identical MACs to a batch of cards. (I have seen this IRL).

Regardless of your reasons, windows XP shows the MAC as follows:

CMD prompt on windows XP with the MAC circled in red

Note that the image is of an ethernet interface. An interface which allows multiple computers on a local network and where it is needed that the multiple NICs on the same network can be identified.

Your question was about dial-up.

That is a connection with only two people on the 'network' (aka phone line). You, and the other side. There is no need for hardware addresses to identify one of many people on the same line.

This means you probably will need to write your own driver to display that extra number. (might be simple, since all you would do is get an existing driver and just add a display line to to. No additional functionality will be used.)

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what I am talking about is this, please take a look at the edited question. – Deb Jul 12 '12 at 8:52
GPRS is a nice blend between a phone line (no MAC needed) and broadcast. Drat. There goes my explanation with a case smack in the middle of (need) and (unneeded). – Hennes Jul 12 '12 at 9:19
If no mac needed then why that physical address is showing on that dialup connection. – Deb Jul 12 '12 at 12:16
Not sure. I read up on GPRS, the GPRS core network etc but all I got are more questions. All I can say is that you do not need ARP (and thus no MAC) on point to point connections (PPP== point to point protocol). You do need it when you are broadcasting on a wire (or, I guess, into the ether). Where GPRS fits, how it is tunnels via UMTS and GSM is unclear to me. – Hennes Jul 12 '12 at 12:34

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