@brooksbrown Ok then turning your linux server into a router is pretty simple. You just have to turn on a linux kernel parameter to make it route between the interfaces.
The first thing you need to do is to get FOG imaging correctly. When you setup FOG did you tell it to use the eth1 as your imaging interface?
Also post your config file for the isc dhcp /etc/dhcp/dhcpd.conf
You may want to review this setup for isc dhcp server if you need to support both bios (legacy) and uefi systems: https://wiki.fogproject.org/wiki/index.php?title=BIOS_and_UEFI_Co-Existence
From the error, my bet is that your dhcp configuration is wrong and your dhcp option 66 doesn’t point to the IP address of your eth1 interface.
And finally turning your linux box into a router: http://www.yourownlinux.com/2013/07/how-to-configure-ubuntu-as-router.html
This is the kernel setting you need to enable in sysctl /etc/sysctl.conf
net.ipv4.conf.default.forwarding=1
net.ipv4.conf.all.forwarding=1
But again lets get fog imaging correctly.
If you did not pick the proper settings during fog server install, there is a hidden file that contains the settings in /opt/fog/.fogsettings
just review that file to ensure the settings are correct. If you need to change something make the change there and rerun the installer.