We have been having sporadic DHCP issues that only affect Windows Vista and Windows 7. This has been happening since Friday. Windows XP workstations have had no issues. Issue is quite simply the users on these PCs do not get an IP address.

Explain your network because at the moment your situation doesn't make sense unless it truly is a DHCP Server issue (which this forum doesn't truly cover) OR you have something else going on. What troubleshooting steps have you taken? You said both Vista and Windows 7 computers can't get IP addresses - so that rules out this is a Windows 7 problem on its face, so therefore its a server issue unless you have some other data that can show otherwise. What is the DNS, DHCP and DC operating systems? What is the domain forest level set at? Is this a Microsoft DHCP Server or Samba? Too many pieces of the puzzle missing here.How do you know they are not getting an IP address? When you run NSLOOKUP from those problem machines - what do they report? What other troubleshooting measures have you taken thus far? Have you disabled power saving on the network adapters on the troubled machines? Is network discovery turned on those machines? MCSE, MCSA, MCDST [If this post helps to resolve your issue, please click the "Mark as Answer" or "Helpful" button at the top of this message. By marking a post as Answered, or Helpful you help others find the answer faster.]

What is the DHCP server? Is it a router? This issue occurs if the security programs in Windows Vista and Windows 7 systems block broadcast packages from network so the DHCP packs cannot be received. I suggest you temporarily disable the programs and check the result. Also please upgrade the drivers for the network adapters. If the issue still occurs, I suggest you refer the following article and follow the steps in all Windows Vista computers. Windows Vista cannot obtain an IP address from certain routers or from certain non-Microsoft DHCP servers In Windows 7, the default value of DhcpConnEnableBcastFlagToggle is 1. You can check it in Windows 7 systems. If on any computer the value is 0, change it to 1 and check the result. If the DHCP server is a router, also please upgrade the firmware for the router.Arthur Xie - MSFT