I know, it isn't supposed to happen - but it did on my network. I have two identical systems with the same MAC addresses - I found this out by looking at the DHCP tables and realized that they had been assigned the same IP addresses - then I noticed that they had the same MAC addresses as well... I have intermittent errors with those machines - especially one of them. What errors will having duplicate MAC addresses & IP addresses cause, and what do I do?

dear friend if you have both computers in the same network you are ahving ip address conflicts and the machine that pretends to send packets to one of them is confused because this ip address. As I know it is not posible to have two mac address identical, and it is a carachteristic of the interfeace pc board. ALL OF THEM ARE DIFFERENT. CHANGE THE IP ADDRESS OF ONE OF YOUR PC´S. HAVE A NICE TIME RAUL DELGADO

Actually you can have identical MAC addresses... although it's very rare to happen unless you intentionally set it up. (You simply spoof to the computer what MAC your hardware reports.... this is usually possible through the network adapter's property page... or you can use the software SMAC.)

Actually it really does happen in cross-market products (rarely). Change the MAC address in the OS and everything is fine (lots of programs indexed in Google that can do this, or even a howto to manually change it). "What errors will having duplicate MAC addresses & IP addresses cause, and what do I do?" I would not waste my time discovering this, as it entirely depends on the TCP/IP stack implementation of a particular OS. It might be worth a security exploit, but I doubt it.