Which of the following TCP packet flags indicates that host should IMMEDIATELY terminate the connection containing the packet?

FIN signals a graceful connection teardown, allowing the receiving side to finish sending data before closing, not an immediate termination.

URG marks data in the segment as urgent and prioritizes it for processing, but does not affect connection state at all.

SYN is used to initiate a new TCP connection during the three-way handshake, not to terminate one.

The RST (Reset) flag instructs the receiving host to immediately abort the connection without a normal teardown handshake. Unlike FIN, there is no waiting for acknowledgment or graceful close - the connection is torn down instantly and any in-flight data is discarded. This is used when a connection is in an invalid state or must be forcibly closed.