TCP Connection Lifecycle

From SYN to FIN — the complete lifecycle of a TCP connection, traced through the Linux kernel. Learn why packet loss cascades into application latency, why HTTP/2 head-of-line blocking is a TCP problem not an HTTP problem, and how congestion control shapes every connection.

Launch Simulator →

What you'll explore

  1. 01

    3-Way Handshake

    SYN → SYN-ACK → ACK. Three packets, two round trips, one established connection.

  2. 02

    Data Transfer

    Sliding window, ACK clock, and the mechanics of reliable delivery.

  3. 03

    Congestion Control

    Slow start, AIMD, and why your connection shapes itself to the network.

  4. 04

    Reliability Mechanisms

    Retransmits, SACKs, fast retransmit, and the RTO calculation.

  5. 05

    Teardown & TIME_WAIT

    The 4-way FIN exchange and why TIME_WAIT lasts 2×MSL.

Validated against Linux kernel v6.12.93 — net/ipv4/tcp_input.c and friends. Every simulated behavior cites a real source function.

The simulator is free. Unlock the full kata library, progress tracking, and weak-area analysis with zerohop Pro.

Launch Simulator →