Oh, neat! Never noticed that option in the Wireguard app before. That's very helpful already. Regarding your opnsense setup:

I've dabbled in some (simple) routing before, but I'm far from anything one could call competent in that regard and even if I'd read up properly before writing my own routes/rules, I'd probably still wouldn't trust that I hadn't forgotten something to e.g. prevent IP/DNS leaks.

I'm mainly relying on a Docker and was hoping for pointers on how to configure a Wireguard host container to route only internet traffic through another Wireguard Client container.

I found this example, which is pretty close to my ideal setup. I'll read up on that.

My problem with this solution was that I have signed in to Tailscale via my Google account, and I have to buy Mullvad through Tailscale, linking my Google account to the Mullvad account.

What I wanted to do was have my own Mullvad account and route Tailscale through it, but that wasn't possible, I had to have Tailscale manage Mullvad, which just didn't sit right with me.

Your browser gives them enough information to profile you by they don’t really need your ip address.

I've been tempted by Tailscale a few times before, but I don't want to depend on their proprietary clients and control server. The latter could be solved by selfhosting Headscale, but at this point I figure that going for a basic Wireguard setup is probably easier to maintain.

I'd like to have a look at your rules setup, I'm especially curious if/how you approached the event of the commercial VPN Wireguard tunnel(s) on your exit node(s) going down, which depending on the setup may send requests meant to go through the commercial VPN through your VPS exit node.

Personally, I ended up with two Wireguard containers in the target LAN, a wireguard-server and a **wireguard-client **container.

They both share a docker network with a specific subnet {DOCKER_SUBNET} and wireguard-client has a static IP {WG_CLIENT_IP} in that subnet.

The wireguard-client has a slightly altered standard config to establish a tunnel to an external endpoint, a commercial VPN in this case:

[Interface]
PrivateKey = XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Address = XXXXXXXXXXXXXXXXXXX

PostUp = iptables -t nat -A POSTROUTING -o wg+ -j MASQUERADE
PreDown = iptables -t nat -D POSTROUTING -o wg+ -j MASQUERADE

PostUp = iptables -I OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT && ip6tables -I OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT

PreDown = iptables -D OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT && ip6tables -D OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT

[Peer]
PublicKey = XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
AllowedIPs = 0.0.0.0/0,::0/0
Endpoint = XXXXXXXXXXXXXXXXXXXX

where

PostUp = iptables -t nat -A POSTROUTING -o wg+ -j MASQUERADE
PreDown = iptables -t nat -D POSTROUTING -o wg+ -j MASQUERADE

are responsible for properly routing traffic coming in from outside the container and

PostUp = iptables -I OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT && ip6tables -I OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT

PreDown = iptables -D OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT && ip6tables -D OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT

is your standard kill-switch meant to block traffic going out of any network interface except the tunnel interface in the event of the tunnel going down.

The wireguard-server container has these PostUPs and -Downs:

PostUp = iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

default rules that come with the template and allow for routing packets through the server tunnel

PostUp = wg set wg0 fwmark 51820

the traffic out of the tunnel interface get marked

PostUp = ip -4 route add 0.0.0.0/0 via {WG_CLIENT_IP} table 51820

add a rule to routing table 51820 for routing all packets through the wireguard-client container

PostUp = ip -4 rule add not fwmark 51820 table 51820

packets not marked should use routing table 51820

PostUp = ip -4 rule add table main suppress_prefixlength 0

respect manual rules added to main routing table

PostUp = ip route add {LAN_SUBNET} via {DOCKER_SUBNET_GATEWAY_IP} dev eth0

route packages with a destination in {LAN_SUBNET} to the actual {LAN_SUBNET} of the host

PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE; ip route del {LAN_SUBNET} via {DOCKER_SUBNET_GATEWAY_IP} dev eth0

delete those rules after the tunnel goes down

PostUp = iptables -I OUTPUT ! -o %i -m mark ! --mark 0xca6c -m addrtype ! --dst-type LOCAL -j REJECT && ip6tables -I OUTPUT ! -o %i -m mark ! --mark 0xca6c -m addrtype ! --dst-type LOCAL -j REJECT
PreDown = iptables -D OUTPUT ! -o %i -m mark ! --mark 0xca6c -m addrtype ! --dst-type LOCAL -j REJECT && ip6tables -D OUTPUT ! -o %i -m mark ! --mark 0xca6c -m addrtype ! --dst-type LOCAL -j REJECT

Basically the same kill-switch as in wireguard-client, but with the mark manually substituted since the command it relied on didn't work in my server container for some reason and AFAIK the mark actually doesn't change.

Now do I actually need the kill-switch in wireguard-server? Is the kill-switch in wireguard-client sufficient? I'm not even sure anymore.

Oh I'm fully aware. I personally don't care, but one could add a capable VPS and deploy the Wireguard Host Container + two Client Containers, one for the LAN and one for the commercial VPN (like so), if the internet connection of the LAN in question isn't sufficient.