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Enable LAN Access in Mullvad Wireguard Configuration Files

734 words; 4 minute(s)

Table of Contents

Download Configuration Files from Mullvad

To begin, you'll need Wireguard configuration files from Mullvad. You can choose any of the options as you download them. For example, I enabled the kill switch, selected all countries, and selected a few content filters.

Once downloaded, unzip the files and move them to the Wireguard folder on your system.

cd ~/Downloads
unzip mullvad_wireguard_linux_all_all.zip
doas mv *.conf /etc/wireguard/

Configuration File Layout

The default configuration files will look something like this:

[Interface]
# Device: <redacted>
PrivateKey = <redacted>
Address = <redacted>
DNS = <redacted>
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 = <redacted>
AllowedIPs = <redacted>
Endpoint = <redacted>

Note: If you didn't select the kill switch option, you won't see the PostUp and PreDown lines. In this case, you'll need to modify the script below to simply append those lines to the [Interface] block.

Editing the Configuration Files

Once you have the files, you'll need to edit them and replace the PostUp and PreDown lines to enable LAN access.

I recommend that you do this process as root, since you'll need to be able to access files in /etc/wireguard, which are generally owned by root. You can also try using sudo or doas, but I didn't test that scenario so you may need to adjust, as necessary.

su

Create the Python file that we'll be using to update the Wireguard configuration files.

nano replace.py

Within the Python file, copy and paste the logic below. This script will open a directory, loop through every configuration file within the directory, and replace the PostUp and PreDown lines with the new LAN-enabled iptables commands.

Note: If your LAN is on a subnet other than 192.168.1.0/24, you'll need to update the Python script below appropriately.

import os
import fileinput

print("--- starting ---")

dir = "/etc/wireguard/"

for file in os.listdir(dir):
    print(os.path.join(dir, file))
    for line in fileinput.input(os.path.join(dir, file), inplace=True):
        if "PostUp" in line:
            print("PostUp = iptables -I OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL ! -d 192.168.1.0/24 -j REJECT && ip6tables -I OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT")
        elif "PreDown" in line:
            print("PreDown = iptables -D OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL ! -d 192.168.1.0/24 -j REJECT && ip6tables -D OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT")
        else:
            print(line, end="")

print("--- done ---")

Once you're done, save and close the file. You can now run the Python script and watch as each file is updated.

python3 replace.py

To confirm it worked, you can cat one of the configuration files to inspect the new logic and connect to one to test it out.

cat /etc/wireguard/us-chi-wg-001.conf

The configuration files should now look like this:

[Interface]
# Device: <redacted>
PrivateKey = <redacted>
Address = <redacted>
DNS = <redacted>
PostUp = iptables -I OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL ! -d 192.168.1.0/24 -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 ! -d 192.168.1.0/24 -j REJECT && ip6tables -D OUTPUT ! -o %i -m mark ! --mark $(wg show %i fwmark) -m addrtype ! --dst-type LOCAL -j REJECT

[Peer]
PublicKey = <redacted>
AllowedIPs = <redacted>
Endpoint = <redacted>

If you connect to a Wireguard interface, such as us-chi-wg-001, you can test your SSH functionality and see that it works even while on the VPN.

wg-quick up us-chi-wg-001
ssh user@lan-host

To confirm your VPN connection, you can curl Mullvad's connection API:

curl https://am.i.mullvad.net/connected
# You are connected to Mullvad (server us-chi-wg-001). Your IP address is <redacted>