Settings: this is a quad CPU machine, plenty strong, not loaded at all (neither CPU nor network), the client is a Windows Server 2008 64bit, the server is a linux box.
I have four threads that are all issuing HTTP requests starting at the same time. The connections are initiated to IPs X, X, Y, Z (two connections to X, one to Y and Z). All targets are on the local LAN.
I am seeing that connections to X, Y and Z are formed (SYN-SYN/ACK), and the second connection to to X is with a 100 ms delay. Meaning, the machine is not sending the second SYN to X for a full 100 ms.
Could this be related to TCP Offload Engine? What else could be causing this delay?
Edit - Another suspect is the client code - it's written in Java, uses HttpURLConnection.