What is the TCP three-way handshake?

The TCP three-way handshake is the SYN, SYN-ACK, and ACK exchange used to establish a TCP connection.

Why are TCP states important?

TCP states help diagnose connection setup, transfer, firewall, load balancer, and termination behavior.

TCP Handshake Debugger

Q: How is TCP different from UDP?

TCP establishes a reliable connection before data transfer, while UDP sends datagrams without a connection handshake.

Visualize the sequence of SYN, ACK, and FIN flags to understand how reliable network connections are established and closed.

CLIENT

SYN

SERVER

Use controls below to initiate connection.

What does the TCP State Analyzer do?

This tool visualizes the TCP connection lifecycle, including the three-way handshake and graceful termination. It shows how SYN, SYN-ACK, ACK, FIN, and related states move a session from closed to established and back again.

Why TCP states matter

Many application issues are really connection issues. Understanding TCP states helps explain blocked ports, half-open sessions, firewall drops, load balancer behavior, slow starts, and why a service may accept connections but fail during data transfer.

Who benefits from it?

Network students, sysadmins, firewall engineers, developers, support teams, and anyone learning packet analysis can use it to make TCP behavior easier to see.

FAQ

What is the three-way handshake? It is the SYN, SYN-ACK, ACK exchange that establishes a TCP connection.

Why does TCP use states? States track where each side is in connection setup, data transfer, and shutdown.

How is TCP different from UDP? TCP is connection-oriented and reliable, while UDP sends datagrams without establishing a session first.