ACK (TCP Acknowledgment)
The ACK control bit acknowledges receipt of TCP segments and advances the acknowledgment number during the three‑way handshake and normal data transfer.
#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
An ACK indicates that data with a sequence number less than the acknowledgment value has been received.
RFC RFC 793 (TCP) [Obsoleted by RFC 9293] (1981-09) Informative evidence
The acknowledgment field contains the next sequence number the sender of the acknowledgment expects to receive.
Mappings
Network+ TCP/IP CISSP Domain 4
More context
ACK is used in the TCP three‑way handshake (SYN → SYN‑ACK → ACK) and throughout a connection to confirm receipt and support reliable, in‑order delivery.