Local discovery between two phones with Hotspot of one not working, global discovery very slow

[martin-braun]

Description of the issue

I have a setup of 3 devices that have Syncthing installed:

• Pixel 3a (provides a local network with a Hotspot)
• Galaxy S10
• MacBook

I'm using your fork on the mobile devices. The MacBook and the Galaxy S10 is connected to the Hotspot of the Pixel 3a. The Syncthing-Fork on Pixel 3a and Galaxy S10 is currently in force mode, so no run conditions play a role here. I setup a folder to be synced on all devices.

In the device tab, they will only connect with the MacBook. If I disable Syncthing on the MacBook, it will not solve the issue.

All devices have NAT Traversal, Global Discovery and Relaying off, as I want to transmit only via local network.

If I enable global discovery on the mobile devices, they will connect with each other after a very long discovery time of almost 5 minutes, eventually.

Reproduction Steps

• Two Android Devices with a shared folder
• Both devices run Syncthing-Fork with NAT Traversal / Global Discovery and Enable Relaying being off (only Local Discovery is on)
• One device has a hotspot open that the other device is connected to
• Both devices are added and share a folder (everything is setup on each device properly)
• Force mode is enabled
• Wait 10 minutes to see nothing is happening
• Enable Global Discovery (for test purposes)
• Wait 5 minutes to see they connect eventually

Version Information

• App Version: 1.20.3.1
• Syncthing Version: v1.20.3

Pixel 3a

• Android Version: Android 12 (Kernel 4.9.292-gab4493f31457)
• Device manufacturer: Google
• Device model: Pixel 3a
• Device platform info (adb shell "getprop | grep ro.product"):

  [ro.product.bootimage.model]: [Pixel 3a]
  [ro.product.build.date]: [Mon May  9 18:24:52 UTC 2022]
  [ro.product.model]: [Pixel 3a]
  [ro.product.odm.model]: [Pixel 3a]
  [ro.product.product.model]: [Pixel 3a]
  [ro.product.system_ext.model]: [Pixel 3a]
  [ro.product.vendor.model]: [Pixel 3a]
  [ro.product.vendor_dlkm.model]: [Pixel 3a]

Galaxy S10

• Android Version: Android 12 (Kernel 4.14.113-24166302)
• Device manufacturer: Samsung
• Device model: Galaxy S10
• Device platform info (adb shell "getprop | grep ro.product"):

Android Log (Pixel 3a)

Syncthing-Fork running and force enabled on Galaxy S10 right before starting Syncthing-Fork and enabling force on Pixel 3a to sync two folders: https://gist.githubusercontent.com/martin-braun/419be2140f1773d42fd9f971ed98722f/raw/d33b7cb2b3a22ce56e1736280c218c1f9d41fb12/logcat.log

[Catfriend1]

Hi,

this is duplicate of issue #801 . Local discovery is limited by Android. You need to configure static IP addresses.

[martin-braun]

@Catfriend1 Thanks for looking into this. Seems familiar indeed. Could you please open the referenced issue at least, even when you cannot work on this?

What I also don't understand is that our phones were connected, but now they never are again. So we can only sync when my MacBook is on as well. Not optimal.