Cracking the Code: Demystifying the TCP Three-Way Handshake with Visuals and Practical Scenarios

Explanation of the TCP Three-Way Handshake:

1. Step 1: SYN (Synchronize) – Computer A to Computer B:

   • Computer A (the client) initiates the connection by sending a TCP packet with the SYN flag set. The packet includes an initial sequence number, let’s say 1000.
   • This packet is sent to Computer B (the server), indicating that Computer A wants to establish a connection.

2. Step 2: SYN-ACK (Synchronize-Acknowledge) – Computer B to Computer A:

   • Upon receiving the SYN packet, Computer B acknowledges the request by sending a TCP packet with both the SYN and ACK flags set. It also includes its initial sequence number, let’s say 3000, and acknowledges the receipt of the SYN packet by incrementing the sequence number to 1001.
   • This packet signals that Computer B is willing to establish a connection and is ready to receive data.

3. Step 3: ACK (Acknowledge) – Computer A to Computer B:

   • Finally, Computer A responds by sending a TCP packet with the ACK flag set. It acknowledges the receipt of Computer B’s SYN-ACK packet by incrementing the sequence number to 3001.
   • This completes the three-way handshake, indicating that both devices are synchronized and ready to exchange data reliably.

Example of the TCP Three-Way Handshake:

Let’s say you want to access a website using your web browser (Computer A), and the website’s server (Computer B) needs to establish a TCP connection to deliver the web page. The three-way handshake process ensures a reliable connection is established before data transfer begins.

1. Computer A sends a SYN packet to the web server (Computer B) to initiate the connection request.
2. The web server (Computer B) receives the SYN packet, acknowledges it with a SYN-ACK packet, and indicates its readiness to establish a connection.
3. Computer A acknowledges the web server’s response with an ACK packet, confirming the successful establishment of the connection.