Hello from Toronto,
Here is a quick post. What are the ports that are needed by AD? How can you verify they are open from a client? How can you test this? Port Query!
This will run through all the pre-defined AD ports and verify the client is able to connect. There are serveral built in categories including Exchange, SQL as well as allowing you to manually define your own range. The best part this is just a GUI on top of another tool portqry.exe. This should replace the need to install the Telnet client as this is not available by default in Windows Vista/2008 and greater.
Mark "Goodnight Canada" Morowczynski