What causes a TCP/IP reset (RST) flag to be sent?

Question

I\'m trying to figure out why my app\'s TCP/IP connection keeps hiccuping every 10 minutes (exactly, within 1-2 seconds). I ran Wireshark and discovered that after 10 minut

Answer 1

RST is sent by the side doing the active close because it is the side which sends the last ACK. So if it receives FIN from the side doing the passive close in a wrong state, it sends a RST packet which indicates other side that an error has occured.

Answer 2

A 'router' could be doing anything - particularly NAT, which might involve any amount of bug-ridden messing with traffic...

One reason a device will send a RST is in response to receiving a packet for a closed socket.

It's hard to give a firm but general answer, because every possible perversion has been visited on TCP since its inception, and all sorts of people might be inserting RSTs in an attempt to block traffic. (Some 'national firewalls' work like this, for example.)