I am measuring a time of about 100-150 milliseconds from sending TCP SYN to getting SYN/ACK, between two linux computers connected to the same Cisco switch. Consider:
- The machines are very powerful, and neither them nor the switch is heavily loaded.
- From analyzing tcpdumps logs on the two machines I see the problem is not in the endpoints but rather in the network itself (the client sees 100-150 ms delay, but the server processes the responses in about 10 ms).
- Only SYN requests are slow. Afterwards, a normal TCP packets gets an ACK right away.
So, my questions are:
- Am I right to think this is way, way too much?
- What latency should I aim for?
- What can I do to further diagnose and solve the issue?
Edit - We've taken the switch out of the equation. The two computers are now connected in a cross cable, and we're still seeing the problem. Both are on full duplex, 100 MBPS.