TCP three way handshake

1
votes

In the TCP three way handshake connection procedure does the client (the one who initiated the connection) send to the server any data payload joined with the ACK packet in the third step ?

1
tcp

1 Answers

2
votes

The last ACK in the TCP handshake can already contain a payload. But, this is usually not done since the application first calls connect and then will either wait for the server to reply or send its first data. Since the kernel does not know what the application will do next it will already send out the ACK within the connect so that the server knows as fast as possible that the connection is established.

Depending on your OS it might be possible to change this behavior and send the ACK together with the first data. In Linux this can be achieved by explicitly disabling quick ack before connecting:

int off = 0;
setsockopt(fd, IPPROTO_TCP, TCP_QUICKACK, &off, sizeof(off)); 
connect(fd,...)