Before I begin, I didn't set up any of the network in our system. I would have configured things very differently.
That being said, we have several VLANs, and two Win2008 DHCP servers assigning from different pools on each subnet. The DHCP servers are on a different subnet from most of the clients. The router forwards the DHCP requests to the servers' subnet/VLAN. I suppose the requests are acknowledged by whichever server sees them first.
Anyhow, while I realize that this setup is not ideal, it's been working fine until today, when clients on one VLAN began not getting IP addresses.
On one PC, the system log shows a DHCP error timestamped every second. The message is:
The IP address lease 0.0.0.0 for the Network Card with network address 001EC9... has been denied by the DHCP server 10.1.1.10 (The DHCP Server sent a DHCPNACK message).
The message seems to alternate between the two servers' addresses.
I do not see anything DHCP-related in the event logs on the servers. The workstation's MAC does not appear in the leases on either server. My current workaround has been to assign a static address to any PC that's not getting an address. I've rebooted both servers this morning. In at least one case, a PC had a valid IP address, then lost it after coming back from sleep mode.
The servers run DHCP for 20 VLANs and only one is having this issue. No configurations have changed. I'm stumped.