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TCP Connection Lifecycle: From SYN to FIN

Beginner

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TCP: reliable, ordered, connection-oriented

TCP guarantees that data arrives in order and without corruption — but this reliability requires connection setup, sequence tracking, and graceful teardown. Each phase has specific state transitions.

Understanding this lifecycle explains common developer experiences: 'connection refused' (no LISTEN), 'connection reset' (RST), port exhaustion (too many TIME_WAIT), and slow first requests (handshake RTT).

Packets in motion — click to inspect:

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