Access to hosts on my local network work fine. Access to hosts on the Internet, via a NAT gateway (a Cisco device), are either very slow or do not work at all. Over time, the access appears to further slowdown. Local access continues to work fine. I have used a variety of devices - the Marvell Yukon NIC, a RealTek NIC, an old 3COM 905c PCI card, and something from LinkSys. All cards display exactly the same problem. I have tried the various suggestions of turning off checksums, no help. I have tried a variety of drivers, no help. On the Beta 2 release of Vista I had no troubles. All this is new with RC1 (the original, plus the recently released RC1 refresh). I am starting to suspect it is an interaction with NAT on the Cisco - could this be possible? Any ideas, suggestions, or fixes? Thank you!

Hello siegeld, Did you try the following command netsh interface tcp set global autotuninglevel=disabled It's working nice for me (Marvell Yukon and Realtek)! It's a tips waiting the right solution. I know some Cisco device like Pix with old firmwares have an issue with Windows products (RFC 1323).At present, I don't know more, I try to get more information.

Thanks. That did fix the problem. I appreciate it very much!