Question : Duplicate IP address

Hi all,

I know this is a common topic and many answers have been posted on the topic, but I can't seem to figure this out! I have a client that has about 50 users, but they're in and out of the office multiple times a day -- they're independent realtors each with a laptop -- so I can never really tell who's in the office and who isn't.

Every few days I get a message on the server saying that it has an IP conflict with another computer on the network. Unfortunately, people at the office don't always notice this and it may be a few hours before they call me. On a few occasions when I was there and it happened,  I disconnected the server from the network and tried to ping the address and nothing replied back until I reconnected the server.

The network is a simple W2K server running DHCP serving IP addresses in the 10.0.0.100 - 10.0.0.205 range. The server's static IP address is 10.0.0.245. I can see in the Event Log that each time this happens, it puts an error in the log saying that the server has a conflict with MAC address 00:0F:66:E9:FF:D7. However, I can't figure out what device that is!

I've run IPSCAN to get a listing of what devices are out there and it always matches up to what it should be, i.e., all devices with known static IP address (printers, wireless access points) are all accounted for.

My problem is that it seems like this device with a duplicate IP address is only on the network for a short period of time and I can never catch it!

Any ideas on how to get to the bottom of this? Is there a way to block access to the network based on knowing the MAC address?

Thanks,

Tom

Answer : Duplicate IP address

The only way that you can block access is on the switch - but your hardware is not capable of doing that. There is no other way of blocking access.

Unfortunately an IP scan will not show the device up unless you turn off the server so that the conflict goes away. Depending on the number of users that are on site, you may be forced to visit each one and not allow any to be plugged in until you have checked them.

Simon.