If you notice performance problems on a web server published through ISA, check if there are packets dropped in the firewall log with the published server as Client IP, the client as Destination IP and a Result Code of 0xC0040034 FWX_E_SEQ_ACK_MISMATCH.
If that's the case, try the following steps and see if the problem disappears:
- Update network card drivers to the current version. Reboot afterwards and try if it helped.
- Disable IP offloading by setting EnableRSS, EnableTCPA, EnableTCPChimney to 0, and DisableTaskOffload to 1 (create the REG_DWORDs if necessary) in HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip\ Parameters on ISA and the published servers. Reboot afterwards and try if it helped.
- In the the To tab of the publishing rule, activate "Requests appear to come from the ISA Server computer" instead of "Requests appear to come from the original client". The last change did fix the problem for me, it has some disadvantages though as you don't have the actual client ip in the web server logs.