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Three-Way Handshake

The TCP setup exchange (SYN, SYN-ACK, ACK) that establishes a connection between two endpoints. Foundational to understanding networking and to recognizing many TCP-based attack patterns.

TCP's three-way handshake establishes a reliable connection: the initiator sends SYN, the responder replies SYN-ACK, the initiator confirms with ACK. Recognizing it is foundational networking literacy and matters for defenders: SYN floods, half-open connection abuses, and reconnaissance scans all manifest as specific patterns at this layer. Reading packet captures, interpreting firewall logs, and analyzing connection-rate anomalies all start from understanding this handshake.

Introduced in: Networking Foundations

Examples

  • Reading a packet capture showing the SYN, SYN-ACK, ACK exchange.
  • Recognizing a SYN flood by half-open connections piling up.
  • Interpreting connection-rate anomalies via TCP-handshake patterns.