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[Solved][Kinda] Server blocking LAN responses over Wireguard VPN (lemmy.world)

submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]

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I'm trying to setup Wireguard to use as a VPN on my server using this guide. I currently run Pihole on the same machine.


LAN	192.168.1.*
WG	10.14.0.*
WG Server Addr	10.14.0.1
WG Client Addr	10.14.0.10

The handshake succeeds, and I can even ping IP addresses. However, it doesn't receive DNS responses. I checked in Wireshark and see the following:


WAN Client IP ->	Server IP	[Wireguard]
WG Client IP ->	Server IP	[DNS Request]
Server IP ->	Server IP	[DNS Request]
Server IP ->	Server IP	[DNS Response]
WG Server Addr ->	WG Client Addr	[DNS Response]
WG Client Addr ->	WG Server Addr	[ICMP Port unreachable]

I'm admittedly pretty inexperienced when it comes to routing, but I've been at this for days with no success. Any help would be greatly appreciated.

Edit

I now realize that it would have been relevant to mention the my Pihole instance was running inside a rootless podman container.

To test things further, I wrote a small echo server and spun it up on bare metal. Wireguard had no issues with that. My guess is that something between wireguard and specifically rootless podman was going wrong. I still don't know what, unfortunately.

My fix was to put Pihole in a privileged podman container with a network and static IP e.g. --net bridge:ip=10.88.0.230. I also put wireguard into a privileged podman container on the same network --net bridge. Finally, I set the peer DNS to the Pihole's static IP on the podman network (10.88.0.230).

As I said before, I still don't know why podman wasn't replying to the correct IP initially. I'm happy with my fix, but I'd still prefer the containers to be rootless so feel free to message me if you have any suggestions.

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[–] [email protected] 1 points 1 year ago

Is it the server telling the server that the client's port is unreachable or is it the client telling the server that the port is unreachable? Do you see the packets traveling over the Wireguard interface? Do you see the response if you use Wireguard from the client?

The request traced out is incorrect. WG Client IP initiates a DNS request to Server IP, and then WG Client Addr receives a response from WG Server Addr. The DNS response should come from the same IP that the request was sent to. The client may be rejecting a response coming from an unexpected source. If you're doing masquerading instead of plain routing, you need to make sure that you're doing NAT in both directions.