Why is the FIN flag in TCP called FIN?

Question

There are some flags in TCP. I already understand what other flag names come from, such as SYN stands for synchronization. I also know that FIN is used to close a connection. What I don't understand is what exactly FIN means. Is it an abbreviation like other flags? I just can't make sense of it.

Solution

Why is the FIN flag in TCP called FIN?

FIN is an abbreviation for "Finish"

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In the normal case, each side terminates its end of the connection by sending a special message with the FIN (finish) bit set. This message, sometimes called a FIN, serves as a connection termination request to the other device, while also possibly carrying data like a regular segment. The device receiving the FIN responds with an acknowledgment to the FIN to indicate that it was received. The connection as a whole is not considered terminated until both sides have finished the shut down procedure by sending a FIN and receiving an ACK.

Source TCP Connection Termination :

Comments

[CharlesH]

I'm pretty sure FIN is just short for finish in everything I've ever studied :)

[Tetsujin]

It's also French for 'end', which is probably how finish got into the English language in the first place.

[DavidPostill]

@Tetsujin from Latin originally -- finish Middle English: from Old French feniss-, lengthened stem of fenir, from Latin finire, from finis ‘end.’ ;)