How a VPN Works

🌐 How a VPN Works — Step by Step

Scenario: You’re in India, you pick a US VPN server, and you open YouTube.

1) Pick a server

Your VPN app lists servers (India, US, UK…). You choose one (or “Smart Connect” picks the lowest-latency/least-busy server).

2) Find the server

Your phone/laptop first resolves the server name to an IP (DNS), then tries to talk to it over UDP or TCP.

3) Handshake = private language

Your device and the VPN server do a cryptographic handshake (e.g., TLS for OpenVPN/WireGuard’s own handshake/IKE for IPsec) to:

• Exchange public keys
• Create shared session keys (used for encryption)
• Prove who you are (password/certificate/MFA)

4) Make a “virtual cable”

The VPN app creates a virtual network adapter (TUN/TAP). Think of it as a private cable inside the internet.

5) Change the routes

Your OS installs routes so traffic goes into the tunnel instead of straight to the internet.

• Full-tunnel: everything goes via VPN
• Split-tunnel: only selected apps/sites/subnets go via VPN

It may also switch DNS to the VPN provider to avoid leaks.

6) Wrap your packets (encapsulation)

Each packet you send (e.g., to YouTube) is:

• Encrypted (so no one can read it)
• Wrapped inside a new packet with the VPN server’s IP as the destination

(Original → encrypted → put inside a new outer envelope → sent to VPN server)

7) Server unwraps & forwards

The VPN server decrypts your packet, then forwards it to YouTube as if it’s the server talking.

To YouTube, the source IP = VPN server’s IP (US).

8) Replies come back the same path

YouTube replies → VPN server receives → encrypts → sends back to you → your device decrypts → app plays the video.

9) Keep the tunnel healthy

The app sends keepalives, occasionally rekeys (new session keys), and watches for drops.

10) If the server is busy or down

Your app detects timeout/high latency/packet loss. It fails over to the nearest or next-best server (based on ping/packet loss/load). While switching, your stream may buffer (the tunnel is being re-thrown).

11) When you disconnect

Routes and DNS revert. If you enabled a Kill Switch, your device blocks internet until the tunnel is back (prevents IP/DNS leaks).

12) Performance basics (why VPN can feel fast or slow)

• Latency (ping): Extra hop to the VPN server adds delay. Closer server = lower latency.
• Bandwidth (Mbps): Your final speed is the slowest link: your ISP ↔ VPN server capacity ↔ site capacity.
• Protocol:
  • WireGuard: modern, fast, low-overhead (usually best latency/speed)
  • OpenVPN: very compatible, solid, more overhead
  • IPsec/IKEv2: great for mobile (handles network changes well)

📦 Buffering & “Server Busy/Down” in Plain Words

If your chosen server is overloaded (too many users), packets wait in line → higher latency, lower throughput → your player drains its buffer → stutters. If the server goes down, your app reroutes to another server. That gap is when buffering happens. Even with high Mbps, if latency spikes during reroute or the server is congested, your player may still pause.

🔀 Full vs Split Tunnel (why it matters)

• Full-tunnel: Privacy everywhere, but more latency for all apps.
• Split-tunnel: Only chosen apps/sites use VPN; others go direct → less buffering for the rest.

🧭 India↔US Examples (quick sanity checks)

• You in India → US VPN → Indian website: route goes India → US (VPN) → back to India (site) → US → India. That’s extra distance → higher latency → potential buffering.
• You in India → India VPN → Indian website: shortest path via local VPN → lower latency, good for streaming.

🧠 Tiny Mnemonic: H-E-A-R-T

• Hello (find server + handshake)
• Encrypt (make session keys)
• Adapt routes (full/split, DNS)
• Relay (server unwraps & forwards)
• Trust but verify (kill switch, rekey, failover)

⚠️ What a VPN does not do

• It doesn’t make you magically anonymous to everyone: the VPN provider can see your real IP and when you connect.
• It can’t fix a slow ISP line or a congested streaming service.

🧩 Minimal ASCII path (drop in your slides)

[Your App]
    │ original packet (You → YouTube)
    ▼
[VPN Client] --encrypt+encapsulate-->
    ▼
[Internet]  (outer IP dest = VPN Server)
    ▼
[VPN Server] --decrypt--> forward to YouTube
    ▼
[YouTube] --reply--> VPN Server --encrypt--> You