VPN, Proxy, and Datacenter IP Detection: How It Works

Streaming providers (like Netflix), financial institutions, e-commerce storefronts, and gaming networks actively detect whether an incoming connection originates from a real residential broadband connection or an intermediary proxy/VPN.

When our lookup tool marks an IP address with a Hosting or VPN/Proxy flag, how does it know?

The Anatomy of Proxy and VPN Detection

Detecting an intermediary IP address involves combining several deterministic technical indicators and heuristic threat intelligence feeds:

1. ASN and Datacenter Classification

Commercial VPN providers and proxies run their server software inside cloud datacenters (such as Amazon Web Services, DigitalOcean, Linode, OVH, or Hetzner).

By checking the Autonomous System Number (ASN) and RDAP registry details, detection systems immediately categorize the IP as a datacenter/hosting allocation. Because ordinary residential consumers do not have servers in AWS as their primary home internet line, any traffic originating from these ASNs is instantly flagged.

2. Active Port and Protocol Scanning

Many public and residential proxy servers run listening software on common proxy ports:

• HTTP / HTTPS proxies: Ports 8080, 3128, 8000
• SOCKS4 / SOCKS5 proxies: Port 1080
• OpenVPN: Port 1194
• WireGuard: Port 51820

Threat intelligence providers continuously port-scan the Internet, maintaining live databases of IP addresses that accept proxy connection handshakes.

3. Public Tor Exit Node Directory

The Tor anonymity network is open by design. The Tor Project publishes a public, real-time list of all active Tor Exit Nodes. Security engines download this directory every few minutes. If an IP matches a known exit node, it is 100% confirmed as Tor traffic.

4. TCP/IP Stack Fingerprinting (p0f)

Different operating systems configure their TCP/IP network packet headers with distinct default values:

• TCP Window Size
• Initial Time to Live (TTL)
• Maximum Segment Size (MSS)
• Selective Acknowledgment (SACK) behavior

If your browser user-agent claims you are using Windows 11, but the incoming TCP packet parameters match a Linux 6.x kernel running on a datacenter server, the system detects that an intermediate proxy tunnel is terminating the connection.

5. WebRTC and DNS Leak Heuristics

When a user visits a webpage through a VPN, the webpage JavaScript can trigger a WebRTC peer connection query. If the browser’s local interface reports an internal IP or geographic timezone that conflicts with the IP address reported by the HTTP connection, a proxy setup is detected.

Why Legitimate Users are Flagged

VPN detection is crucial for stopping automated credential stuffing bots and payment fraud. However, privacy-conscious users running personal VPNs or iCloud Private Relay often get flagged inadvertently by over-aggressive detection algorithms.