The clients are running on the machine #1. The server is installed on the machine #2. The machines have a gigabit connection through a switch on their private vlan. There are no errors in the switch log. The clients and ping command use internal IP address. The CPU load on both machines is lower than 50% but rarely spikes to 100%.
Usually ping tells <1ms but randomly "Request timed out" or something like 400ms.
I see better results (70ms spikes) when I ping from another machine but when I connect more clients another machine shows "Request timed out" too.
There are no related warning in the windows event log.
What can cause that?