Three-way handshake
03Both endpoints synchronize their initial sequence numbers before ordinary data transfer.
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“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 3.5 ↗
RFC 9293 · § 3.5EXAMPLE
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04
Complete synchronization.
The server enters ESTABLISHED after the valid acknowledgment.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
Read the updated RFC section ↗
Acknowledge both initial sequence numbers.
- SYN consumes one sequence number in each direction.
- The final ACK acknowledges the server SYN.
- TCP also supports simultaneous open; the familiar client-server exchange is one path through the state machine.
The handshake synchronizes transport state. It does not authenticate the peer or negotiate encryption.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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