DNS Issues with Wireguard for Windows

[Andrew Burkett]

I was running into dns issues with wireguard on windows using the
released gui app. It seems like a bug with wireguard, but not sure if
it was actually something about my networking configs that messed it
up. I was able to work around the issue by changing the wireguard
config (in a way that seemed odd to me), but I thought it might be
useful to share what I was seeing in case its helpful to others or if
it is in fact a bug in wireguard. I'll share the configs at the bottom
of the email, but I'm just going to describe what I'm seeing first.

My basic setup is I have wireguard running on a linux box functioning
as a server/router to a remote network. I've got a windows desktop
connecting to the linux box via wireguard. There are dns servers on
the remote network that I would like to use from the desktop. I added
the dns servers from the remote network to my desktop wireguard
config. Everything was working fine for awhile. At some point, my
windows box started complaining about not being connected to the
internet. I was able to pinpoint it with some confidence to dns
requests failing when wireguard was connected. Even though windows was
complaining about not having a network connection, my browser still
worked though it seemed slow so I assumed it was trying a dns server
and then falling back to a different one after a timeout (at least
that was my guess). The "cause" of the problem was adding
192.168.7.12/32 to the AllowedIPs on the peer (the wireguard network
in my case is 10.98.1.0/24 and the rest of the network is under
10.0.X.X) After adding it and waiting for a couple hours windows will
inevitably claim that there is no internet access from my network
adapter. Sometimes nslookup and ping still work fine, sometimes they
start to report errors. My solution that reliably fixes it is to add
my local dns server (which is my local router in this case
192.168.86.1) to the dns section of the wireguard config, which seems
like an odd fix since I'm not actually sending local dns traffic to
wireguard.

I couldn't figure out how to use wireshark to view wireguard traffic
on windows to see what's happening to the dns requests, nor do I know
of another way to view traffic (If someone wants to point me at how to
do that, or some other way to view network traffic on windows, I'm
happy to look at it).

Anyway, thanks for the software. It's the best vpn software I've used by a mile.

Andrew

My Local Gateway/DNS is 192.168.86.1
My Local IP is in 192.168.86.0/24 subnet

Working Config 1

[Interface]
PrivateKey = XXXXX
Address = 10.98.1.103/32
DNS = 10.0.X.X, 10.0.Y.Y

[Peer]
PublicKey = XXXXXX
AllowedIPs = 10.0.0.0/16, 10.98.1.0/24
Endpoint = XXXXXXX

Working Config 2

[Interface]
PrivateKey = XXXXX
Address = 10.98.1.103/32
DNS = 10.0.X.X, 10.0.Y.Y , 192.168.86.1

[Peer]
PublicKey = XXXXXX
AllowedIPs = 10.0.0.0/16, 10.98.1.0/24, 198.168.7.12/32
Endpoint = XXXXXXX

NonWorking Config

[Interface]
PrivateKey = XXXXX
Address = 10.98.1.103/32
DNS = 10.0.X.X, 10.0.Y.Y

[Peer]
PublicKey = XXXXXX
AllowedIPs = 10.0.0.0/16, 10.98.1.0/24, 198.168.7.12/32
Endpoint = XXXXXXX