VPN Detection by Apps & Services

TL;DR

Apps and services can detect VPN use through your IP address, DNS leaks, WebRTC leaks, port numbers, and inconsistencies in user behaviour. While a good VPN hides your IP, other methods exist. Using strong VPN settings and additional tools like a firewall or Tor can improve privacy.

How Apps & Services Detect VPNs

Many apps and services actively try to block or restrict users connecting via VPN servers, especially self-hosted ones. Here’s how they do it:

1. IP Address Blacklists

1. How it works: VPN providers use a limited number of IP addresses. These IPs are often added to blacklists used by streaming services, banks, and other platforms.
2. What you can do: Choose a VPN provider with a large IP pool and regularly rotate your IP address. Some premium VPNs offer dedicated IPs (at an extra cost).

2. DNS Leaks

1. How it works: Your computer uses DNS servers to translate website names into IP addresses. If your VPN isn’t configured correctly, your DNS requests might still go through your ISP’s servers, revealing your location even with a changed IP address.
2. What you can do:
   • Ensure your VPN client is using its own DNS servers (check the settings).
   • Use a public DNS server like Cloudflare’s 1.1.1.1 or Google Public DNS (8.8.8.8) within your VPN configuration, but verify it’s actually being used.
   • Test for DNS leaks using online tools like DNSLeakTest.

3. WebRTC Leaks

1. How it works: WebRTC (Web Real-Time Communication) is a technology used for video and audio calls in browsers. It can reveal your real IP address even when using a VPN, bypassing the VPN tunnel.
2. What you can do:
   • Disable WebRTC in your browser settings. The method varies depending on your browser (search online for instructions specific to your browser).
   • Use a browser extension designed to block WebRTC leaks.

4. Port Numbers

1. How it works: VPN connections often use specific port numbers (e.g., 1194 for OpenVPN). Services can identify these ports and flag the connection as coming from a VPN.
2. What you can do: Use a VPN that allows you to change the port number used for your connection. Some VPNs offer obfuscated servers which mask the typical VPN port numbers.

5. Behavioural Analysis

1. How it works: Services monitor user behaviour, such as login locations and browsing patterns. Sudden changes in location or unusual activity can raise suspicion.
2. What you can do: Use the VPN consistently to establish a more normal pattern of usage. Avoid rapid switching between different VPN server locations.

Improving Your Privacy

1. Use a Strong VPN: Choose a reputable VPN provider with strong encryption, a no-logs policy, and features like a kill switch (which cuts your internet connection if the VPN drops).
2. Firewall Configuration: Configure your firewall to only allow traffic through the VPN tunnel. This prevents data leaks if the VPN fails. For example, using iptables on Linux:

   sudo iptables -A OUTPUT -o tun0 -j ACCEPT # Allow outbound traffic via VPN interface
   sudo iptables -A INPUT -i tun0 -j ACCEPT  # Allow inbound traffic via VPN interface
   sudo iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT #Allow established connections
   sudo iptables -A OUTPUT -j DROP # Drop all other outbound traffic

   (Replace tun0 with your actual VPN interface name.)

3. Tor Integration: For maximum privacy, consider using Tor in conjunction with a VPN. This adds an extra layer of anonymity by routing your traffic through multiple relays.
4. Check Your Configuration Regularly: Periodically test for DNS leaks and WebRTC leaks to ensure your VPN is working correctly.