DHCP lease time and IP scope - Something to watch out for...

  • Why does a small crisis only ever happen when you have 200 or so machines to image and a looming deadline ?

    Had a ‘brown afterburner’ moment today when my production FOG server (Ubuntu 12.04 LTS ‘Alternate’ 64 bit / Fog 1.2 stable release with FOG doing the dhcp and tftp serving) all of a sudden just decided it wasn’t going to hand out any more IP addresses thank you very much. All the services were running happily and a restart didn’t clear the problem.

    It turned out to be that the dhcpd.conf file had a very limited scope - just 25 addresses, and a default lease time of around 7 days. The scope was probably my fault because I’d set the IP address of the Fog server to something daft - instead of something more sensible like, but the very odd thing was that rebooting the server didn’t seem to release the previously offered dhcp leases ? Wierd. Editing the dhcpd.conf file to more sensible numbers has fixed the issue.

    Anyway, just in case this helps somebody in future…


  • I’m perhaps a little unusual in that all of my ‘customers’ are vehicle based laptops rather than desktops. Add to this that I’m not allowed to make any sort of connection to the company LAN (which sports very potent network access control anyway) and I have to have FOG on an isolated network.

    At home though for my sandpit system like yourself I’m running pfSense on a repurposed Watchguard appliance with it doing the dhcp and tftp stuff.

    I really expected that a reboot of the FOG server would have cleared the dhcp leases. We live and learn…


  • Moderator

    I guess I’m lucky that Windows Server or pfsense usually does my DHCP. you must be imaging on a different network to your main machines.

    what made you decide not to put the imaging service on your main network so you could image any PC at any time?