So today I was using Syncthing to sync some files with my phone (GrapheneOS) from a Linux computer. I was using Local Discovery and Nat Traversal as the options on both.

I am behind Rethink DNS app on android and I had to disable Always on VPN option on my phone and had to select Exclude from DNS and Firewall option fn the Synching-Fork on Rethink in order for it to work locally. But before I did that I saw some DNS connections Syncthing-Fork was making, to STUN providers such as stun.internetcalls.com.

I believe you can stop these connections by turning off NAT Traversal .

But this got me thinking how private is Syncthing? Are the STUN servers seeing what I am sending? And yes the transfer was happening locally. I saw TCP LAN in the transfer info.

Syncthing-Fork is from F-Droid.