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Dev.to
7/13/2026
The original title is: "One TCP Connection, From SYN to FIN: Capture the Whole Lifecycle in tcpdump"

The original title is: "One TCP Connection, From SYN to FIN: Capture the Whole Lifecycle in tcpdump"

Original: One TCP Connection, From SYN to FIN: Capture the Whole Lifecycle in tcpdump

Short summary

A hands-on Protocol Lab tutorial that walks through capturing a complete TCP connection lifecycle — from three-way handshake to four-way teardown — using tcpdump in a two-node containerlab topology. The lab covers SYN/ACK/FIN/RST flags, sequence numbers, and state transitions per RFC 9293, with an echo server built via socat. Expected completion time is 50–65 minutes.

  • •Capture and annotate a full TCP lifecycle: SYN handshake, data exchange, FIN teardown
  • •Learn tcpdump flag notation and sequence/acknowledgment number mechanics
  • •Uses a simple two-node containerlab topology with netshoot containers

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