Duplicate IP Addresses on LAN

[lifegard2]

I'm running two DHCP scopes on separate servers. The scopes do not overlap and have a lease time of 1 day. The servers are both running Windows Server 2003.

I'm having an issue where a few users are getting "Windows detected a conflict with an IP address" error messages. For the life of me I can not find where the duplicates are coming from. If I can get into the client OS (sometimes I can), IPCONFIG /ALL shows the proper DHCP server pulling from the correct scope of the correct server. When I view the DHCP panel on the server, it only shows a single lease to the affected client machine.

I've looked for a Linksys or DLink router on the network thinking maybe that's serving up these IPs, but no joy. Also, the typical cable modem router doesn't setup it's DHCP server in our subnet (192.168.9.xxx).

Has anyone seen anything like this or got any ideas how to track down the offending machines?

 

[karmic]

ok, first of all, how many pc's do you have on both network scopes? What are the IP ranges for the scopes? Are the duplicate ip's always the same?

~ K.I.S.S - Don't make it any more complex than it has to be ~

 

[lifegard2]

I've got about 65 machines total hitting both scopes. The scopes are 192.168.9.51-98 and 192.168.9.100-220.

No, the addresses appear to be different each time. I've seen .68, .100, and .101 that I can recall. When I look in DHCP MMC on server, it shows different addresses each time assigned to the user reporting trouble.

The only way I've been able to work around it is to create a sort of null reservation for the bad address and then create a good reservation for the good address.

I thought maybe I had a rogue DHCP server, but I ran dhcploc and only had the two authorized DHCP servers found.

Since then, I found a setting in DHCP MMC that pings an available address before assigning it to a DHCP client. Hopefully this will prevent dups in the future, but I'd like to know why the dups are happening in the first place.

 

[DTracy]

LifeGard2,

I had this happen to me once, the problem was someone was "helping" me by changing hardware (hard drive) from one workstation to another. This was causing the DHCP to try to replicate that IP on a different workstation. I'm not sure this is your problem but you might have a look around, especially at the laptops, they are the easiest to change out the drives.

Regards,
David.