[Techtalk] DHCP issues

Rudy Zijlstra rudy at grumpydevil.homelinux.org
Mon Sep 24 21:57:20 UTC 2012

Betty Johnson wrote:
> I hope there are some networking gurus out there.
> A month ago, a server failed in my organization and we arranged a quick fix so we could take some time with purchasing new hardware.
> Routers are set up with IP helper so we needed to make the DHCP server with the same IP address as the failed server. The server was a Windows server running DHCP, and file and print services. There was a Debian Linux box running snort and the Linux admin logged on and set this box for DHCP services and changed IP address to the same one that the failed server had.
> Once we purchased our new server and set it up with the same roles as the original one. The Linux server IP address was changed and the new server was given the original IP address for the failed server. Again this was a Windows computer. However, apparently the Linux admin neglected to stop the DHCP daemon on the Linux server. So as a result we had 2 active DHCP servers on the same subnet of our network.
> Now we had all sorts of issues with unable to see shares, unable to browse the network and unable to map network drives.
Basically you are in a situation where you can get double IP addresses. 
In other words, 2 different machines using the same IP address. Yes, 
that can cause all kinds of troubles... or rather, it *will* cause all 
kinds of trouble, including the described problems. It may also cause - 
for example - internet browsing to randomly fail.

Please shut down the unwanted DHCP server. Rebooting the affected 
machines may help to get out of the troubles. Otherwise things will sort 
themselves out after the leases expire (once the unwanted server is shut 
off). But depending on the lease time, that can be a long time...



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