DHCP is a very simply, non-complex technology. If you have the DHCP server(s) on a remote VLAN (not shared with the clients), then you first need to go back and validate that all of your DHCP RElay Agents are configured properly on your routers. Next, if that is correct, you should check your switch configuraitons to ensure that the switch ports are assigned to the correct VLAN. The reasons is because the DHCP server cannot randomly assign IPs from any scope it chooses. The DHCP server will look at the GIADDR portion of the packet to see what VLAN (subnet) the client is coming from, then it finds the matching scope to issue an address from. During this troubleshooting, you should review the DHCP logs (found in %windir%\system32\dhcp) and also take some packet captures on the client and dhcp server subnet to see if the packets are making their way accross for these systems that are affected. I would leave the packet capturing for last, since most of these issues can be resolved with the relay agent or vlan configuraitons on the network gear. Visit anITKB.com, an IT Knowledge Base.

Our 2003 server has 6 dhcp scopes for various vlans. Everything was working until a few days ago. Some machines (not all) are not getting an IP address, after lots of testing I found a work around but not a fix. It only seems to be affecting 2 scopes on the dhcp server, and if you deactivate one scope the PCs on the other scope connect, then if you activate that scope and deactivate the other then the remaining machines connect. Ofcourse this only works until the machine is rebooted. Not all machines on these 2 scopes are affected and I cannot pin point one area of failure.