TCP Fast Open

Question 1

SYN packet

Answer 1

A packet with the SYN[chronize] flag.

It is the TCP packet flag that is used to initiate a TCP connection. A packet containing solely a SYN flag is the first part of the “three-way handshake” of TCP connection initiation

Question 2

SYN-ACK

Answer 2

A packet with the ACK[knowledge] flag.

In response, the server replies with a SYN-ACK.

Question 3

ACK

Answer 3

Finally, the client sends an ACK back to the server.

Question 4

TFO cookie

Answer 4

a cryptographic cookie stored on the client and set upon the initial connection with the server.

When the client later reconnects, it sends the initial SYN packet along with the TFO cookie data to authenticate itself.