Bug 458553

Summary:	android app cannot connect to PC on IPv4 network if IPv6 is blocked
Product:	[Applications] kdeconnect	Reporter:	lvm
Component:	android-application	Assignee:	Albert Vaca Cintora <albertvaka>
Status:	REPORTED ---
Severity:	normal	CC:	hgkamath
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Other
OS:	Android 11.x
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description lvm 2022-08-31 14:15:11 UTC

SUMMARY
I was using KDE connect on android 9 in conjunction with NoRoot firewall (https://play.google.com/store/apps/details?id=app.greyshirts.firewall) for a long time, but after I switched to new android 12 phone I found out that when this firewall is enabled KDE connect cannot see my computer. I tried changing Noroot firewall to another random VPN-type android firewall - Rethink DNS (https://f-droid.org/packages/com.celzero.bravedns/) and got the same result. Then I tried yet another VPN-type firewall - Netpatch (https://play.google.com/store/apps/details?id=co.netpatch.firewall). Like the two previous firewalls, it doesn't support IPv6 filtering, but unlike them it has a switch to disable IPv6 blocking and it did the trick - with IPv6 unblocked KDE connect was able to see my computer again. Obviously, it is insecure as now apps can bypass the firewall using IPv6, so it is not an acceptable solution but at least it indicates the problem: for some reason KDE Connect needs IPv6 even though my WiFi network is IPv4-only. So why does KDE Connect need IPv6 so badly and is it possible to make it work without it? 


STEPS TO REPRODUCE
prerequisites:
Netpatch is installed in android (https://play.google.com/store/apps/details?id=co.netpatch.firewall)
WiFi network is IPv4 only

1. start netpatch, enable it on the main screen, then tap 'network connections' and toggle IPv6 blocking to on - KDE connect cannot see the PC
2. toggle IPv6 blocking to off - KDE connect now can see the PC

OBSERVED RESULT


EXPECTED RESULT
KDE connect should've been able to communicate on both occasions

SOFTWARE/OS VERSIONS
android app: 1.19.1
Android: 12

ADDITIONAL INFORMATION

Comment 1 lvm 2022-09-01 14:14:59 UTC

Also it only affects the initial connection. If connection is established while firewall is disabled, KDE connect continues to operate even after the firewall is re-enabled. Adding devices by IP doesn't help.

Comment 2 GK 2022-10-09 13:18:55 UTC

just confirming that what I see might be this bug.
I have ensured that firewall rules for full-path-to-kdeconnectd.exe to allow any ip-address on either tcp/udp on private/public networks.
wifi in wifi-settings shows that it is private network.
Home wifi router is set to do ipv4 DHCP.
As mentioned, I can ensure device detection and communication between PC and android-app only if windows-firewall for private networks is turned off.

Android-8.0 
On Windows-10 21H2 19044.2075
```
PS C:\WINDOWS\system32> scoop info kdeconnect
Name        : kdeconnect
Description : Communications and data transfer between devices over local networks
Version     : 22.08.0
Bucket      : extras
Website     : https://kdeconnect.kde.org
License     : GPL-3.0-or-later
Updated at  : 9/23/2022 6:53:14 PM
Updated by  : Hu3rror
Installed   : 22.08.0 *global*
Binaries    : bin\kdeconnect-cli.exe
Shortcuts   : KDEConnect
Notes       : If you want to get the latest development branch-based installer, please install `kdeconnect-nightly`
              from Versions bucket.
```