TCP/IP Handshake Walkthrough

Introduction

In this interactive task from the Networking Fundamentals module of TryHackMe's Pre-Security course, we deep dive into how communication begins between two devices over the TCP/IP protocol using a concept known as the 3-way TCP handshake.

Instead of just reading theory, this lab challenges learners to help two virtual characters, Alice and Bob, establish a reliable connection by correctly reassembling the TCP handshake.

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What Is the TCP Handshake?

The 3-way handshake is the foundational process by which two devices establish a TCP connection before transmitting data. It consists of:

1. SYN – Client sends a connection request

2. SYN-ACK – Server acknowledges and agrees to the request

3. ACK – Client confirms, and the connection is established

This ensures both sides are synchronized before actual data transfer begins.

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Static Lab Walkthrough

Lab Objective:

Reorder the packet exchanges between Alice and Bob in the correct sequence to form a proper TCP handshake.

Action Taken:

In the lab simulation, I reviewed the communication logs between Alice and Bob and dragged the three handshake packets into the correct order:

1. Alice sends SYN

2. Bob replies with SYN-ACK

3. Alice responds with ACK

Outcome:

Once the sequence was correctly arranged, the virtual TCP session between Alice and Bob was established successfully, and the lab displayed the flag at the end of the conversation.

Takeaway:

• The TCP handshake is critical for ensuring reliable communication

• Misordered or missing steps = no connection

• Understanding this flow helps with deeper analysis of network behavior (e.g., packet sniffing, intrusion detection)

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Quiz Answer

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Final Thoughts

This task made the TCP/IP model feel far more intuitive. Rather than memorizing steps, I had to apply them in context, reinforcing the importance of handshake integrity in everyday internet communications.

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Skills Practiced

• Packet-level analysis

• Understanding TCP/IP structure

• Visualizing the 3-way handshake

• Data transmission initiation

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Flag Captured

THM{TCP_CHATTER}