A FIN packet is used for a graceful closure of a TCP connection through a four-way handshake, while an RST packet abruptly terminates the connection due to error or unexpected closure.
With respect to closing TCP connections, the main difference between a FIN packet and an RST packet lies in the way they terminate the connection. A FIN packet is used to gracefully close a TCP connection, indicating that a device has finished sending data. It is part of a four-way handshake process in which both ends of the connection are informed and agree to close. Each side of the communication sends a FIN and acknowledges the other's FIN before the connection is closed.
On the other hand, an RST packet, or reset packet, is employed when a connection needs to be aborted immediately. This could be due to an error condition or because one side of the connection has closed unexpectedly. When an RST packet is received, the connection is immediately dropped without any further exchange or proper graceful termination.