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Frequently asked questions

Issues with dynamic server IP

Hostnames cannot be resolved during startup. This may lead to a five minutes delay during boot. A solution to this is to disable the automatic start of the wg interface during start and connect only later (manually) when you are sure that you can resolve hostnames.

  1. Disable auto wg0 in /etc/network/interfaces (put # in front, like #auto wg0)
  2. Start wireguard manually using sudo ifup wg0

If the IP changes while the connection is running, resolving the new IP address fails often. Reconnect using

sudo ifdown wg0 && sudo ifup wg0

To achieve a permanent solution, one can install a cron job which restarts the connection automatically whenever a change is detected. This avoids excessive restarts of the interface. Example script (taken from Ubuntuusers Wiki):

#!/bin/bash
# Check state of wg0 interface
wgstatus=$(wg)
if [ "$wgstatus" == "interface: wg0" ]; then
    ip link delete wg0 && ifup wg0
elif [ "$wgstatus" == "interface: wg0" ]; then
    ifup wg0
else
    file="/tmp/digIP.txt"
    digIP=$(dig +short beispiel2.domain.de) # Change this to your domain !
    if [ -e "$file" ]; then
        fileTXT=$(cat "$file")
        if [ "$digIP" != "$fileTXT" ]; then
            #echo "Daten sind gleich"
            /sbin/ifdown wg0
            /sbin/ifup wg0
            echo "$digIP" > "$file"
        fi
    else
        echo "$digIP" > "$file"
    fi
fi

Store this file as /home/[user name]/wg-restart.sh and add it to your crontab:

sudo crontab -e
*/10 * * * * bash /home/[user name]/wg-restart.sh    # Runs the script every 10 minutes

Routes are periodically reset

Users of NetworkManager should make sure that it is not managing the WireGuard interface(s). For example, create the configuration file /etc/NetworkManager/conf.d/unmanaged.conf with content

[keyfile]
unmanaged-devices=interface-name:wg*

source

Broken DNS resolution

When tunneling all traffic through a WireGuard interface, the connection can become seemingly lost after a while or upon a new connection. This could be caused by a network manager or DHCP client overwriting /etc/resolv.conf. By default, wg-quick uses resolvconf to register new DNS entries (from the DNS keyword in the configuration file). This will cause issues with network managers and DHCP clients that do not use resolvconf, as they will overwrite /etc/resolv.conf thus removing the DNS servers added by wg-quick.

The solution is to use networking software that supports resolvconf.

Hint for Ubuntu users

Users of systemd-resolved should make sure that systemd-resolvconf is installed.

source

Low MTU

Due to too low MTU (lower than 1280), wg-quick may fail to create the WireGuard interface. This can be solved by setting the MTU value in WireGuard configuration in the Interface section on the client:

[Interface]
MTU = 1500

source

Pi-hole not listening on wg0 after reboot

If, e.g., after reboot, the wg0 interface isn't up before Pi-hole is ready (more precisely, the pihole-FTL service is started), you may experience that Pi-hole doesn't listen on the Wireguard interface. This can be mitigated by artificially delaying the start of Pi-hole using, e.g., the config option

DELAY_STARTUP=5

in /etc/pihole/pihole-FTL.conf to have Pi-hole delay the start of the DNS server by 5 seconds.


Last update: September 15, 2021
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