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Tcp header

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

A TCP header is the transport-layer header containing control, addressing, sequencing, acknowledgment, checksum, and flow-control fields for a TCP segment.

A TCP header carries control information that supports connection-oriented communication, sequencing, acknowledgment, retransmission, and flow control. It is at least 20 bytes and can reach 60 bytes when options are included. section 22.2.1

Key TCP header elements include:

  • Source Port and Destination Port identify the endpoints; each field is 16 bits, allowing ports 0–65535. section 22.2.1
  • The Flags field contains eight control bits, including SYN, ACK, and FIN for connection establishment and termination. section 22.2.1

Three-way handshake

PC1 begins with a SYN segment, SRV1 replies with SYN and ACK, and PC1 completes establishment with ACK. These segments contain no application data. section 22.2.1

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes
Defines selected fields and traces their behavior, while treating the complete header primarily as a reference rather than a memorization task.
Examples
Uses PC1 and SRV1 handshake, sequencing, retransmission, termination, and window-size scenarios.
What you can do after
Understand how TCP segments use header fields to establish connections, acknowledge data, retransmit losses, and regulate sending rates.
How it connects
Connects TCP headers with ports, three-way handshakes, sequencing, acknowledgment, retransmission, and flow control.
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