MAC Address Conflicts

use a sniffer to get MAC and IP and then output that to a text file. host names will either be in a dns or on the machine itself.

however, there should never be a MAC duplication unless someone is manually setting the MAC address with software.MAC addresses are burned into the Ethernet Card.

what is the issue you are trying to solve?

As gutridgesj@concord.navy.mil noted, a real MAC address conflict is very rare, and is usually the result of someone changing a MAC address -- generally regarded as a bad thing to do.

You can list your arp (address resolution protocol) cache using the command:
arp -a
from a command window. This lists the IP and MAC address of any machine your machine has talked to within the past two minutes or so. You can ping a few addresses, check the cache, and so on.

If what you are seeing is a message which says that there is an IP conflict with the machine with MAC address , here is how you track it down:

a) If you get this message when you boot your machine, you are trying to grab an IP address that is already in use. The station who is using it has the stated MAC address. If you know what your IP address should be (if not using DHCP), go to another machine and from a command prompt type:
nbtstat -A
(note that the A is capitalized.
This will tell you thenetbios name of the machine with that address and the user logged in (if any).

b) If you are using DHCP, and getting this message when you boot up, you (or your admin) need to look at the DHCP server(s). First, look for the MAC address in the servers' tables. Also, make sure that only one server can give out this IP address. No two DHCP servers should be allowed to give out the same address. Check for rogue servers if your official servers check out. (i.e., some user with a server turned on DHCP.)

c) If you are logged in and get the conflict message at some random time, some other machine (with the stated MAC address) just booted and tried to grab the IP you have. In this case, look for a user complaining that they cannot connect to the internet.

Good luck.