IP Address Conflicts - Mostly on Dell Laptops

[lifegard2]

Hello,

I support a network of around 75 machines. It's a simple AD structure w/ one domain and a single DHCP server on one of the DCs.

Every now and then I'll get a user call me saying they've got the "Windows has detected an IP address conflict" error message in their screen. Typically, I'll go through ipconfig over the phone w/ the user, create what amounts to a null reservation in the DHCP scope so that way no one gets that address again, and then we ipconfig /renew (oh, ipconfig /release then ipconfig /renew renews with the same offending IP address, go figure).

I've run dhcploc on the network, only one DHCP server is responding. I'm the only network admin and my users don't know how to hard code IP addresses.

This typically happens over a wireless connection with Dell laptops, not sure if Dell is the culprit or just coincidence since it's all we have in the laptop arena.

Another workaround is to have the users disable their wireless adapter and then hardwire into the network. This is another way to work around it.

With over 75 machines and only one of me, visiting each workstation to see network settings isn't really an option.

The odd thing is when I turn off a laptop that's claiming to have a duplicate IP address, you'd think I could ping the address and get a response from the other machine on the wire that allegedly has that IP already. This is not the case. Pings in this instance always return unanswered. Additionally, I never get two people calling with this error, just one.

I'm stumped. Any ideas?

There is a Linksys AP on the wire, but it doesn't have a DHCP server. There is also a Linksys WRT54G on the wire, but it's DHCP server is disabled. This error also happened before I installed the WRT54G.

 

[brianinms]

May be an arp cache issue. What kind of switches do you have?

http://support.microsoft.com/kb/q120599/

 

[lifegard2]

Got a few DLink GB switches, an HP ProCurve, and some linksys 10/100's.

 

[lifegard2]

I just ran arp -a on the DHCP server and noted the IP address in question is listed there, so I think this is barking up the right tree.

Now, the DHCP server is also my DC and also one of the DNS servers. I checked both of the other DC/DNS servers and found this IP address listed in each of those as well.

The MAC address it maps to is not one I have documented anywhere. It resolves to an Intel MAC address, but just about all of my desktops are built on Intel motherboards.

I ran arp -d on all three machines. This cleared the entry. Then I attempted to hard code a machine to the offending address (192.168.9.90). Boom, IP conflict. It's showing up in the ARP -a on the DC/DNS servers again.

 

[lifegard2]

The plot thickens. . .

Ok, I traced the MAC down to my mail server. Oddly enough, my mail server has a completely different hard coded IP address on it.

I rebooted all of my main network switches (i.e. those in the phone room, but not those scattered around on user's desks). On the three DC/DNS boxes I ran arp -d *.

After this, I attempted to hard code my workstation to the offending IP address again, 192.168.9.90, same thing, IP address conflict. Magically, the same MAC address is showing up in the ARP table of my three DNS/DC machines.

What am I missing? I know I'm gonna feel like an idiot when I find it, but at least I'll know this stupid thing will be over. It's been going on for a few years now and I'm tired of working around it.

Any ideas?