Connection establishment

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

TCP connection establishment is the process of creating a TCP connection before application data is exchanged.

TCP connection establishment creates a connection before application data is exchanged. It is the first stage of TCP communication, followed by data exchange and connection termination. section 22.2.1

The three-way handshake uses TCP header flags and exchanges three empty segments:

• The client sends a segment with the SYN flag to begin synchronization. section 22.2.1
• The server replies with a segment carrying both SYN and ACK. section 22.2.1
• The client sends an ACK, completing establishment so data exchange can begin. section 22.2.1
• The three handshake segments contain no encapsulated application data; they establish the connection only. section 22.2.1

Figure 22.5 The TCP three-way handshake. PC1 initiates the connection by sending a TCP segment with the SYN flag, SRV1 responds with a segment with the SYN and ACK flags, and finally, PC1 sends a segment with the ACK flag.

Trace the client and server messages in the TCP three-way handshake. section 22.2.1

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

How deep it goes

Explains the three handshake messages and their SYN and ACK flags without detailing TCP implementation internals.

Examples

Uses a client-server handshake diagram involving PC1 and SRV1.

What you can do after

Evaluate TCP traffic by identifying the SYN, SYN-ACK, and ACK sequence.

How it connects

Connects TCP connections with SYN, ACK, data exchange, and connection termination.

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Related concepts

• three-way handshakeincludes · A three-way handshake is the exchange of SYN, SYN/ACK, and ACK messages that establishes a TCP connection between endpoints.
• connection poolingaddressed by · Connection pooling is a resource-management technique that maintains a collection of established connections for reuse across multiple operations.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.