3-Way Handshake

3-Way Handshake

Fundamentally there are 2 main components to the 3-way handshake:

• Bits of the “CODE” field in the TCP header (SYN, ACK, RST...)

• The sequence number.

There are 2 systems involved in the 3-way handshake, an initiator and a

responder,

1. The initiator sends the responder a SYN and the initiators sequence

number.

2. The responder replies with the SYN and ACK bits set in the CODE

field. The initial sequence number of the initiator is incremented

before being returned. The sequence number of the responder is

also sent.

3. The initiator finishes the process with an ACK. Within this ACK, it

returns both the sequence numbers that it has received from the

responder, the responder's sequence number having now been

incremented.

The 3-way handshake establishes 2 important functions:

• It guarantees that both parties are ready to transfer data.

• It allows both parties to agree on initial sequence numbers.