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TCP Connection Establishment: The 3-Way Handshake

TCP Connection Establishment: The 3-Way Handshake

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Nov 4, 2026

In TCP, connection establishment uses a three-way handshake: the client sends a SYN, the server replies with SYN-ACK, and the client sends a final ACK to complete the connection setup.2
So the correct option is (iii) three.

Key terms: SYN , ACK , Initial Sequence Number.

Footnotes

  1. TCP connection establishment (Wikipedia) - Describes the SYN, SYN-ACK, ACK three-way handshake. ↩

  2. RFC 793: Transmission Control Protocol - Core specification describing TCP states and behavior during connection establishment. ↩

TCP 3-Way Handshake Explained

Why TCP needs three steps

The 3-way handshake ensures both sides agree on:

  1. That the other side is reachable (each endpoint gets a response from the other).2
  2. Initial sequence numbers (ISNs) so later data segments can be reliably sequenced and acknowledged.2
  3. That both endpoints are ready to send/receive data for the new connection state.2

A useful conceptual way to view it:

  • Step 1: Client proposes parameters (SYN + ISN)
  • Step 2: Server accepts and responds (SYN-ACK + its ISN)
  • Step 3: Client confirms (ACK acknowledging server’s ISN)

Footnotes

  1. TCP connection establishment (Wikipedia) - Describes the SYN, SYN-ACK, ACK three-way handshake. ↩ ↩2 ↩3

  2. RFC 793: Transmission Control Protocol - Core specification describing TCP states and behavior during connection establishment. ↩ ↩2 ↩3

TCP 3-Way Handshake (Connection Establishment)

  1. 1
    Step 1

    Client sends a SYN segment with its Initial Sequence Number to start the connection.

  2. 2
    Step 2

    Server replies with SYN-ACK: it acknowledges the client’s SYN and includes its own ISN.

  3. 3
    Step 3

    Client sends an ACK acknowledging the server’s SYN, completing establishment so data transfer may begin.

Exam tip: Learn the exact sequence

For TCP connection establishment, memorize: SYN → SYN-ACK → ACK. That pattern directly implies a “three-way handshake.”2

Footnotes

  1. TCP connection establishment (Wikipedia) - Describes the SYN, SYN-ACK, ACK three-way handshake. ↩

  2. RFC 793: Transmission Control Protocol - Core specification describing TCP states and behavior during connection establishment. ↩

Don’t confuse connection establishment with termination

TCP connection termination often uses a “four-step” style (FIN/ACK exchanges), and TLS handshakes are different. The question here is specifically about TCP connection establishment, which is three-way.2

Footnotes

  1. RFC 793: Transmission Control Protocol - Core specification describing TCP states and behavior during connection establishment. ↩

  2. TCP connection termination (Wikipedia) - Explains that termination involves different exchanges (often discussed as a four-step process). ↩

Handshake Steps in TCP Connection Establishment

Each bar represents one distinct message exchanged during setup.

Common Confusions

Connection Establishment Timeline

SYN from Client

1st message

Client initiates connection and proposes an ISN."

SYN-ACK from Server

2nd message

Server acknowledges client SYN and proposes its own ISN."

ACK from Client

3rd message

Client acknowledges the server SYN; connection is established."

TCP Handshake Quick Review

1 / 4
Question · Term

TCP connection establishment uses a ____ way handshake.

Click to reveal
Answer · Definition

Three-way handshake: SYN → SYN-ACK → ACK.

Knowledge Check

Question 1 of 4
Q1Single choice

Connection-establishment in TCP involves a ______-way handshake.

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