![]() ![]() Now, let's take a closer look at what these individual packets look like. I have Cloudflare in front of my website, so this makes sense. ![]() The source (Client) is my computer with IP address 192.168.1.202 and port 18987 and the destination (Server) is a Cloudflare server on 104.18.60.128 on port 443. Note that the length of these packets is 0, since there is no actual data transmitted (it's only a handshake after all). In this packet capture, we can clearly see the SYN, SYN-ACK and ACK packets involved in the 3-way handshake: I used Wireshark to capture the traffic when browsing to my own website, which is the basis for this explanation. Let's dive deeper into the 3-way handshake and see what the network traffic looks like when this handshake takes place. The sequence number is a topic by itself, but this simplified explanation is enough for the purpose of explaining the TCP 3-way handshake. This way both parties can keep track of the amount of bytes that were sent, allowing for reliable transfer on top of the unreliable IP-protocol. In TCP each byte has a sequence number that is increased for every byte sent. One important feature of this handshake is the synchronization of the TCP sequence numbers. Only after the connection has been established, data transfer takes place. No data is sent during the 3-way handshake. Note that I use the terms client and server to clearly distinguish the party that initiates the handshake (client) from the one responding to that (server). Now the session begins and the socket is created.
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