How VPNs really work. Under the hood | by Hussein Nasser | Medium
VPN is often explained as this magical encrypted tunnel that “protects” your identity. But these descriptions are very abstract and often sometimes misleading. I’m not an expert in networking but I know enough to explain what really happens under the hood when you enable a VPN. So I’m going to assume I’m talking to software engineers (those are my audience after all) To know how VPN works, here is a simple example with an http server. Let’s say you want to connect to Google (e.g. IP 1.2.3.4) port 80 let us assume your source ip is 6.6.6.6. This is really your public router IP and not your private laptop IP so I’m going to skip NAT for simplicity. Normally with no VPN, your client sends a SYN segment to port 80 that goes into an IP packet with a destination IP 1.2.3.4 and source ip 6.6.6.6 and Google replies back directly to you with a SYN/ACK destination IP 6.6.6.6 and source IP 1.2.3.4 and this goes on. Your ISP sees the IP packet you are sending back and forth to 1.2.3.4. They can ch
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