ACK

TCP flags are various types of flag bits present in the TCP header. Each of them has its own significance. They initiate connections, carry data, and tear down connections. The commonly used TCP flags are SYN, ACK, RST, FIN, URG, PSH.

• SYN (synchronize): Packets that are used to initiate a connection.
• ACK (acknowledgment): Packets that are used to confirm that the data packets have been received, also used to confirm the initiation request and tear down requests.
• RST (reset): Signify the connection is down or maybe the service is not accepting the requests.
• FIN (finish): Indicate that the connection is being torn down. Both the sender and receiver send the FIN packets to gracefully terminate the connection.
• PSH (push): Indicate that the incoming data should be passed on directly to the application instead of getting buffered.
• URG (urgent): Indicate that the data that the packet is carrying should be processed immediately by the TCP stack