What is TCP SYN/ACK?

Great question! Since you just learned about the SYN packet (the "knock on the door"), the SYN/ACK is the next logical step in the process.

In network terms, SYN/ACK stands for Synchronize-Acknowledgment. It is the second step of the TCP Three-Way Handshake.

How it fits into the "Handshake":

Think of it like a polite phone conversation:

1. SYN (Step 1): Client says, "Hello, I want to talk to you. Here is my sequence number."
2. SYN/ACK (Step 2): Server replies, "Hello! I heard you (ACK). I also want to talk to you (SYN). Here is my sequence number." <-- This is what you asked about!
3. ACK (Step 3): Client replies, "Got it! Let's start sending data."

Why is SYN/ACK important?

• Confirmation: It proves the server is online and willing to accept connections on that specific port.
• Security: If you see a SYN but never see a SYN/ACK, it means the connection was either dropped by a firewall or the port is closed.

How to see them in Wireshark:

If you want to filter specifically for these "reply" packets, you can use this display filter:

tcp.flags.syn == 1 and tcp.flags.ack == 1

If you apply this filter in your current lab, you are looking at the successful "handshakes" where a server has confirmed it is ready to communicate.

Does that help clarify the connection process?