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adventures into the land of the command line

the tcp handshake process

TCP three-way handshake:

0a. the server must first bind to and listen at a port to open it up for connection.

0b. a client may initiate a connection.

1. SYN: The active open is performed by the client sending a SYN to the server. The client sets the segment's sequence number to a random value A.

2. SYN-ACK: In response, the server replies with a SYN-ACK. The acknowledgment number is set to one more than the received sequence number i.e. A+1, and the sequence number that the server chooses for the packet is another random number, B.

3. ACK: Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgement value i.e. A+1, and the acknowledgement number is set to one more than the received sequence number i.e. B+1.

At this point, both the client and server have received an acknowledgment of the connection. The steps 1, 2 establish the connection parameter (sequence number) for one direction and it is acknowledged. The steps 2, 3 establish the connection parameter (sequence number) for the other direction and it is acknowledged. With these, a full-duplex communication is established.