Android App not setting DNS when allowed IPS not 0.0.0.0/0

[Mauro Santos <registo.mailling@gmail.com>]

Hello,

Like the subject says I have found that when I'm not routing all traffic
through the vpn then my dns setting seems to be ignored (tested with
nsleaktest.com).

If I route all traffic through the vpn then it works as expected.

home network: 192.168.20.0/24

vpn "server" is at 192.168.20.10 and internal vpn address is 10.4.4.1,
where I have the dns server running and a few other services accessible
only though the vpn.

"server" config (with systemd-networkd)
wireguard.netdev:
[NetDev]
Name = wireguard
Kind = wireguard
Description = WireGuard VPN

[WireGuard]
ListenPort = 4911
PrivateKey = ...
#Publickey = ...

# Phone
[WireGuardPeer]
PublicKey = ...
AllowedIPs = 10.4.4.3/32

wireguard.network
[Match]
Name = wireguard

[Network]
Address = 10.4.4.1/24

"client" config (android vpn app):
[Interface]
name: msi
public key: ...
addresses: 10.4.4.3/32
dns servers: 10.4.4.1

[Peer]
public key: ...
allowed ips: 10.4.4.0/24
endpoint: 192.168.20.10:4911

The problem also persists if I access the vpn from outside my internal
network and is "fixed" if I change the allowed ips from 10.4.4.0/24 to
0.0.0.0/0.

From what I have searched, other people with similar problems had a
configuration problem, but I don't think it is the case here since my
dns servers in on the same machine as other services and I can access
the other services without problems.

Any ideas on what the problem could be? I have checked the log on the
android app but none of the messages in the log seems to indicate any
problem, should I be looking for some warning/error messages in particular?

-- 
Mauro Santos