SYN (TCP Synchronize)
The SYN control bit starts a TCP connection by initiating the three‑way handshake; a SYN packet indicates a request to synchronize sequence numbers.
#network#rfc#tcp
Last updated: 2025-08-22T00:00:00.000Z
Differences across sources
Parallel sources use distinct terminology or emphasize different aspects.
Review each citation to understand scope and normative intent.
Evidence
RFC RFC 9293 (Transmission Control Protocol) (2022-08) Normative evidence
A TCP connection is initiated by an active opener sending a SYN segment to the passive opener.
RFC RFC 793 (TCP) [Obsoleted by RFC 9293] (1981-09) Informative evidence
The synchronization (SYN) segment is used to initiate a connection.
Mappings
Network+ TCP/IP CISSP Domain 4
More context
SYN is the first step of the TCP three‑way handshake (SYN → SYN‑ACK → ACK). It establishes initial sequence numbers and negotiates connection parameters.