Support DNS routing when connecting through Android tethering

[maikeriva]

Describe the bug Assume the following network structure:

• A WiFi router in a censored country
• A laptop, running Fedora Linux and latest Outline Client appimage
• An android phone, running the latest Outline Client app from the Google Play store

Both the smartphone and the laptop, when connected to the WiFi router, can connect to my Outline server correctly and bypass censorship. When however I activate my phone's wifi tethering and connect my laptop through it (meaning: Router on censored internet <-> Android tethering <-> Laptop) Outline on the laptop seems to connect, but internet is inaccessible (even non-censored websites). Having Outline activated on the smartphone makes apparently no difference (as expected, since tethering traffic cannot be routed through the virtual VPN in Android).

I suspect a routing issue, I am available for troubleshooting guidance.

To reproduce Use a similar setup as outlined above.

Expected behavior Outline should work as it does in a non-tethered setup

Client system (please complete the following information):

• Outline Client Version: Appimage 1.11.0 (468189)
• Your Operating System: Fedora 36

[maikeriva]

Investigated a little. External IP is correctly detected to be the Outline server's one. DNS leak test shows that DNS requests are not routed through Outline. Tethering via USB or Wifi leads to same symptoms.

So I guess it is a DNS routing issue. Any idea on why the different behaviour when tethering?

[gkirgizov]

I experience the same issue on iOS. Both laptop & iphone can independently connect to my Outline server through their Outline clients. But with I use iphone as a hotspot for the laptop , laptop's public IP is visible, and the traffic is not routed through the Outline server. I would consider this problem highly relevant, as this problem defeats the purpose of using VPN. Anything going through the spot with VPN should be going in expected way.