Ran into an interesting issue when accessing a Windows 2003 domain controller from a Windows 2008 server via a gigabit interface connected to gigabit switch.

I was trying to access a Windows 2003 domain controller (HP BL460c) attached to a 1000Mb switch (Cisco 2960) from a Windows 2008 blade server (BL460c) connected to the same 1000Mb switch (Cisco 2960). Performance was terrible. I was having trouble accessing shares on the 2003 DC and the Network Policy Server was not responding to authentication requests when the server had a secure channel to this DC. However, when I had a secure channel to another Windows 2003 DC (HP DL380) connected to a 100Mb switch (Cisco 3550), I had no problems. The solution was to simply install the QoS Packet Scheduler for the Windows 2003 DC (BL460c). This took care of the issue.