TELECOM Digest OnLine - Sorted: Re: Change MAC Address Can Change IP Address of a Machine?

Re: Change MAC Address Can Change IP Address of a Machine?

Jim Hatfield (jim.hatfield@insignia.com)
Fri, 30 Sep 2005 18:10:01 +0100

On 29 Sep 2005 08:10:37 -0700, jrefactors@hotmail.com wrote:

> Is there any way to change the MAC address of a machine? IP address is
> assigned by ISP. My understanding is that IP address is based on the
> MAC address of a machine, is that correct concept?

The Mac address is a property of the Ethernet interface, so if that is
provided by a card such as a PCI or PCMCIA card, changing it for a
different one will change the Mac address.

The IP address is not necessarily based on the Mac address. If you get
IP assignment by DHCP (and maybe PPPoE but I'm not familiar with that)
you will get a free address from a pool assigned at random. You may
then get to keep the same IP address so long as the Mac address of
your PC does not change but this is not guaranteed. For example my
girlfriend's PC will get a different IP address if she power cycles
her cable modem, even though her PC's Mac address does not
change. This is a pain because my firewall is set up to allow her IP
address to connect to my POP3 server and so I have to change the
setting whenever she does this.

-- Jim Hatfield

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