I have a simple application, that up until now has worked on every system it's been tried on. It's a basic command/response system with one client, one server and one connection between them. ie, client sends a packet to the server, server sends packet back to the client. However, something strange is happening on one network, that hasn't been seen anywhere else. On that network, any computer (have tried 2) will connect to the server and send packets as normal. However, randomly (slightly based on frequency of commands being sent out) instead of sending out the data for the next packet, a RST is sent out to the server instead, closing the connection. Has anyone seen this? We looked at ethereal traffic on the network and nothing seems out of place. The only oddity is that the clients send out a PSH with each packet (shouldn't matter) and there is a cisco packet, which according to my research is a benign packet used to detect circular routing among the switches. I'm stumped on this one, and not sure what to do to start tracking it down.

Checking who sends the RST would be the first thing to do. Then go to that machine, and examine the network stack implementation for why it would send a RST.

The main case I've heard of where this happens is some home gateways that will reset a connection if it's been idle for some number of minutes (like 10).