tcp reset

RESET is a flag in TCP packets to indicate that the conection is not longer working. So, if any of the two participants in a TCP connection send a packet contains such a RESET flag, the connection will be closed immediately

 

When an unexpected TCP packet arrives at a host, that host usually responds by sending a reset packet back on the same connection. A reset packet is simply one with no payload and with the RST bit set in the TCP header flags.

There are a few circumstances in which a TCP packet might not be expected; the two most common are:

1. The packet is an initial SYN packet trying to establish a connection to a server port on which no process is listening.

2. The packet arrives on a TCP connection that was previously established, but the local application already closed its socket or exited and the OS closed the socket.