NLB TCP Reset caused by Receive Side Scaling

I experienced many random connection problems trying to reach two Windows 2003 R2 64bit using Network Load Balancing Service.

I analyzed the connection timeout behavior using Network Monitor, when I was able to connect, I could see the TCP three-way handshake, when I got timeout, it returned TCP Reset.

I do a lot of testing but none of the following works:
- change cable
- upgrade NIC Firrmware
- reinstall drivers
- reset TCP stack

After investigating with Microsoft Support, I disabled RSS (Receive Side Scaling) and everything worked properly !

Receive Side Scaling enables parallelized processing of received packets on multiple processors.

I also found that other people experienced Receive Side Scaling problems on ISA Server.

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About Vittorio Pavesi