ok, I'm not shure if this is still hot, but I'm actualy experiencing with dhcp problems on Windows 7 too and I found this one:
after disabeling the Windows Firewall the client gets IP Address from DHCP Server, but however - this cannot be the solution...
So the problem seems to be that the dhcp relay agent sends the dhcp packets as unicast and the Windows 7 machine expects and only accepts dhcp broadcast packets... Is there any way to make the dhcp relay agent sending the dhcp packets as broadcast and not as unicast???
If there is any solution for this one - any help is highly appreciated...
first is the windows PC in different network segment?
example DHCP server is in 10.0.1.0 and the PC is in 10.0.2.0
If this is the case you need enable the DHCP Helper on router where the PC is installed and set the helper with address of the DHCP server.
this is a problem of your system side there is no configuration issues, so to verify kindly plug another PCs or laptop on same port in same vlan
only the Windows 7 machines which are not in same network segment as the DHCP Server do have this Problem...
in other words: Only Win7 machines which do not have L2 connectivity to DHCP Server have this Problem!
When I disable the Win7 Firewall everything works fine, the machine gets and accepts IP Address from DHCP Server...
Win7 machines in the same Network segment as DHCP Server (L2 connectivity) work fine even with Win7 Firewall enabled!
XP machines do not have any problem, they work fine in both network segments...
ip-helper address is configured, as stated bofore XP machines work fine, so the general dhcp config seems to be ok...
Aso with wireshark I see the dhcp offers the win7 machine definitly gets from dhcp Server, but the machine does not accept this offer from dhcp Server - only when I disable the win7 Firewall everything works perfekt!
With Win7 Firewall enabled I also can see the DENIED dhcp offers in the Win7 Firewall logfile!
I am not familiar yet with windows 7 but we are installing those in our environment, and we did have the same problem with one or two of those, but after we did the command "Ip config /release" and and then "IP config /renew" the PC got the right IP address. Also since I do not know your network environment. I suggest that you open the port on PC firewalls for the DHCP server by adding the IP of it and the port. Other problem may occurred form IPV6 Windows 7 supports IPV6 and the PC may try to get the IPV6 if you have older switch and routers that does not support and that may cause the problem. If all equipment working fine with windows older version then looks like it is a PC network configuration.
If you have switches in that subnet I also suggest clearing the ARP table and the MAC-address dynamic table. With slow networks the time to keep alive of this tables is in order of hours sometime.
Final contact your WAN service provider and findout if they are blocking any traffic. Reviewing the description of the problem it looks like it is a routing issue.
On our vlan interfaces we had configured ip broadcast address "subnet.255". Now I changed the ip broadcast address on vlan interface to 255.255.255.255 and now the win7 clients get their ip addresses via dhcp...
But there seems to be a problem too, because from time to time some of the win7 clients claim that there is an ip address conflicct with ip 0.0.0.0 and hardware address 00-0a-b8-ad-7d-38, and this mac-address is the mac from the interface (of cisco switch) to which the win7 client is connected...
I have checked the dhcp server but everything looks fine... I have no idea why there should be an address conflict with this interface???
At this point I would recommend opening a SEV 1 Cisco TAC case and a SEV 1 with Microsoft, they should have an answer for you.- It seems you have done a complete TSHOOT session.
Cisco TAC will usually request a WebEx Session to share your desktop.