DPI and VPNs: diagnosing traffic filtering
DPI examines traffic using protocol and flow characteristics. A single timeout cannot identify a filtering mechanism or its operator.
Content of the article
DPI examines traffic using protocol and flow characteristics. A single timeout cannot identify a filtering mechanism or its operator.
Practical checks
A VPN failure does not prove protocol filtering: DNS, packet loss, incorrect time, MTU and configuration mistakes can look similar. Start with a reproducible test and save a working configuration. Get administrator approval on managed networks; do not bypass workplace policies.
Check ordinary HTTPS without the tunnel, VPN hostname resolution and the configured transport. Compare the same configuration on another permitted network. Separate tunnel establishment from traffic inside it: successful login does not prove that routing and DNS work.
Change one setting at a time. Determine MTU through measurement rather than a universal number. Do not disable certificate verification or device protection to connect. If UDP is unavailable, use only a fallback supported by your gateway and client. For support, collect the time, client version, error code and a redacted log. Restore the original settings after the test; do not publish keys, internal resource addresses or complete user logs.
Official documentation
Publisher: vpn.how