How to verify Win DHCP Server is pushing Option 252
Posted on 2009-12-22
We have a Windows Server 2003 DHCP server with Option 252 set for multiple DHCP scopes.
What I want to verify is that the DHCP server is actually pushing Option 252 to client computers (Windows XP SP2).
Was told that Win DHCP, by default, pushes all DHCP options to all PC's. Therefore, once we set Option 252 assumed it was being pushed to all computers. But we are finding that is not the case.
1. Multiple domain environment with multiple WPAD addresses, one per domain (yes thsi stinks, but that is the environment currently and we need to work with it.)
2. We are trying to push WPAD settings through DHCP (Unable to do this through GPO due to infrastructure configuration, otherwise we would.)
3. Have a PC which should be receiving Option 252 via DHCP but IE does not get the WPAD settings. (i.e. user cannot get to Internet with Automatically detect settings checked in IE. PC is getting lease from correct DHCP server)
4. IE should pick up WPAD setting from DNS after checking DHCP but it is not. PC's are in Domain2 and WPAD setting is in Domain1. Unfortunately WPAD settings exist in both domains, WPAD.Domain1.com and WPAD.Domain2.com.
5. Same PC has Firefox and that is getting the correct WPAD settings (i.e. user can get to the Internet using Automatically detect settings option)
6. Advised that Firefox does not use DHCP for WPAD and instead uses DNS, which makes sense as to why Firefox works but IE does not.
7. Not sure why Firefox resolves WPAD correctly via DNS but IE does not.
8. Best guess on the IE vs Firefox difference is that IE is appending the PC domain suffix to WPAD and thus goes to WPAD.Domain2.com, which is wrong. And Firefox is using the DNS suffix search list to append to WPAD and gets WPAD.Domain1.com because we have forced Domain1.com to be at the top of the DNS suffix list.
9. Used Wireshark to capture DHCP REQ and ACK packets. In the DHCP ACK it shows the options being pushed by DHCP server and no Option 252 shows up.