All machines on our 192.168.206.x subnet (mostly Mac's, with
Windows servers) got the IP conflict message when they started up in
They all have static IP addresses
We do have a linux dhcp server running on that subnet, but it only
hands out 2 IP addresses for barcode guns, and those are given the IP
based on their MAC address, so each barcode gun always gets the same
IP and can move to other buildings without reconfiguring them, as they
run in dhcp mode.
Windows clients and servers didn't seem to get the IP conflict error
The error on each Mac OS X client, showed the same MAC address as
the machine who was using that IP address. No matter what the IP
(unique of course), they all showed the same MAC address, which is the
MAC address of our backbone switch, which is at 192.168.200.3
(different subnet). That switch does routing and has the VLAN for the
As a work-around, I added a bunch more IP's to our dhcp server on the
.200 subnet, and shutdown the dhcp server on the .206 subnet, so the
clients would get IP addresses from the .200 subnet (which would then
route everything back to the .206 subnet) This worked fine, but
introduced a little lag to the .206 subnet.
Our main switch (the one that was listed as the machine who was using
all those IP addresses) is a HP Pro-curve 2900-24G. We found a group
specializing in HP switches to dial-in through our VPN this morning to
see if he could track down and fix our problem. He poked around and
the only thing he wanted to change was to take out the 'proxyarp'
setting in the 2900-24G, and once he did that, the problem was solved.
This setting was in the switch ever since it was deployed some 3 years
ago now, and the issue just happened yesterday. Kind of strange, but
he said that there could have been a cable that got crimped or
sometimes he sees OS updates cause strange issues like this.
See also Dealing with Duplicate IP addresses and Mysterious Duplicate IP problem solved
Got something to add? Send me email.
Increase ad revenue 50-250% with Ezoic
More Articles by Bruce Garlock
© 2011-04-20 Bruce Garlock