The <a href="https://developer.mozilla.org/en-US/docs/Glossary/TCP">TCP (Transmission Control Protocol)</a> 3-way handshake is a process that establishes a reliable connection between two devices, typically a client and a server, before they can exchange data.
Here's a step-by-step explanation of the TCP 3-way handshake process:
<ol>
<li>Client Sends a SYN (Synchronize) Packet: When the client wants to initiate a connection with the server it sends a TCP packet with the <code>SYN</code> flag set to the server indicating the client's intent to establish a connection.</li>
<li>Server Responds with SYN-ACK Packet: Upon receiving the <code>SYN</code> packet, the server acknowledges the client's request by sending a TCP packet back. This packet has the <code>SYN</code> and <code>ACK</code> (Acknowledge) flags set. The <code>ACK</code> flag indicates the server's acknowledgment of the client's request, and the <code>SYN</code> flag indicates its intent to establish a connection.</li>
<li>Client Acknowledges with an ACK Packet: Once the client receives the <code>SYN-ACK</code> packet from the server, it sends an acknowledgment (<code>ACK</code>) packet back to the server. This packet has the <code>ACK</code> flag set and acknowledges the receipt of the server's response.</li>
</ol>
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Here's a summary of the flags used in each step:
<blockquote>
SYN (Synchronize): Indicates the start of a connection request.
</blockquote>
<blockquote>
ACK (Acknowledge): Acknowledges the receipt of a packet or confirms a connection establishment.
</blockquote>
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After the 3-way handshake is complete, both the client and server can start exchanging data in a reliable and orderly manner. If any of the packets in the handshake process are lost, the sender will retransmit them until a successful handshake is established.

TCP Handshake explained

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