A new Intel Gigabit CT Desktop Adapter has been installed in workstation. In tests with Cat 5, 5e, and 6 cables connected directly to a Motorola SBG6580 SURFboard eXtreme Wireless Cable Modem, I have been unable to consistently establish 1 Gbps connectivity. Sometimes connecting and disconnecting the cable after boot will give a 1 Gbps link. With the router on and the workstation brought up from a reboot or cold boot, the initial link reported by Windows is 100 Mbps. The boot behavior is consistent at 100 Mbps. While running, disconnecting the cable and then reconnecting it may lead to a 1 Gbps link. Tests using a different machine provide a 1 Gbps link. Therefore, it seems that boot time auto-negotiation with the Intel Gigabit CT Desktop Adapter is resulting in a 100 Mbps link, although the connection is capable of 1 Gbps.
Any suggestions for debugging this issue further, work-arounds, or fixes?
Test System Configuration: Microsoft Windows 7 Professional Service Pack 1 64-bit with all updates as of June 3, 2012; Intel drivers as distributed via Microsoft Update; Intel Gigabit CT Desktop Adapter PCIe; Motorola SBG6580 SURFboard eXtreme Wireless Cable Modem; Cat 5, 5e, and 6 tested; The motherboard includes a built-in ethernet port which has been disabled in BIOS. Therefore, this is the only ethernet card in the machine.