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IP Conflicts

IP Conflicts

IP Conflicts

Several of our 95/98 wkstations have been individually coming up with an ip conflict with a certain mac address. We have DHCP Service installed on our PDC's. We have about 6 different domains. Some are complete trusts others are one way trusts. We have a layer 2 switch which will be replaced by a layer 3 switch soon. To fix the problem we just exclude the ip address from the scope which forces the wkstation to obtain another. This fixes the problem but then another computer a few days down the road has the ip conflict with the same hardware address. We have 250 computers in our LAN and I have tried locating that mac address but I can't find it. When you look at the scope and the leased addresses list, the proper machine is leasing that address but that ip conflict message says differently. Any suggestions?

RE: IP Conflicts

If you have 6 different PDC's running DHCP, check the scopes on each one. In a "flat" network scenario like you describe you would need to have each DHCP server giving out a seperate range of IP's with no overlap to eliminate conflicts. Later on when you get a layer 3 switch you may be able to subnet your network, but that would necessitate a complete re-vamping of your TCP/IP scheme.

Some HUB/SWITCH management software (Cabletron's SPEL for example) allows you to do a search on MAC addresses. Another alternative if your switch allows "Port Mirroring" or has a "Roving analysis Port" would be to connect some sort of Sniffer device triggered on the offending MAC address and sniff each port on your switch until you find the offender.

RE: IP Conflicts

Thank you.

RE: IP Conflicts

Here is a web site with the vendor codes for the MAC addresses. Maybe knowing the vendor of the NIC card will help you find it. Also, Network Associates makes a program called Sniffer Basic that will help you in the port Mirroring project. You can download a trail version of the software for this one time fix, but it is a good tool to have around.

Vendor List

Sniffer Basic

RE: IP Conflicts

Have you checked the WINS database to find the name of the offending MAC card that hogs the IP address? We found our hogger was a Jet Direct card set for DHCP that got the IP address but it didn't get registered as used in the database for some reason...

Failing that try sending a message to the IP address along the lines of phone me.


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