The system proxy only captures programs that agree to honour the system proxy setting. Many command-line tools, games and background services ignore it entirely, so their traffic leaks out. TUN mode exists to fix exactly this.

How it works

TUN creates a virtual network adapter and points the system's default route at it. All of the machine's network traffic enters this virtual adapter first and is handled uniformly by the proxy — whether a program “knows” about the proxy no longer matters. This is also called a “global transparent proxy”.

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When to use it

  • Software that ignores the system proxy (Git, Docker, some games, Steam downloads, etc.).
  • When you want the whole machine's traffic managed with nothing leaking.

Watch out for

  • TUN needs administrator / root rights to create the adapter and change routes.
  • Get routing right, or even subscription updates and DNS may loop back into the proxy, causing loops.
  • Turn TUN off before stopping the proxy; a crash can occasionally leave route remnants that break networking — restart networking or reset the adapter to recover.
For everyday browsing the system proxy is enough. TUN is the heavy tool for when a program stubbornly won't use the proxy — don't enable it by default.