Why is traditional VPN traffic (OpenVPN, WireGuard) easy for DPI to detect and block?

Classic VPN protocols have recognisable fingerprints — distinctive packet headers, typical ports, unique handshake byte-sequences, and a constant encrypted stream — so DPI can identify and block them.

Deep Packet Inspection detects traditional VPNs through:

• Protocol fingerprint: OpenVPN uses specific packet headers.
• Port patterns: typically port 1194 (UDP) or 443 (TCP).
• Handshake signature: unique byte sequences during connection setup.
• Traffic timing: a constant encrypted data stream with no idle gaps.

Result: VPN traffic is identified and blocked. This is exactly why, in censored environments, a plain VPN often stops working — and why disguising tools (like Trojan proxies and pluggable transports) exist.

Tip: A VPN is encrypted but not disguised — it looks obviously like "a VPN." The next evolution is making the traffic look like something boring and ubiquitous, e.g. ordinary HTTPS.

Go deeper:

• Deep packet inspection (Wikipedia) — how DPI fingerprints protocols by header/port/handshake patterns.