====== Using systemd-resolved ======

===== Configure NetworkManager =====

Edit the /etc/NetworkManager/NetworkManager.conf file, and set the following entry in the [main] section:

    dns=systemd-resolved

Reload the NetworkManager service:

    # systemctl reload NetworkManager
    
Force adjusting of /etc/resolv.conf
    netconfig update -f

Verification steps

Verify that the nameserver entry in the /etc/resolv.conf file refers to 127.0.0.53:

    # cat /etc/resolv.conf
    nameserver 127.0.0.53

Verify that the systemd-resolved service listens on port 53 on the local IP address 127.0.0.53:

    # netstat -tulpn | grep "127.0.0.53:53"
    tcp   0   0 127.0.0.53:53   0.0.0.0:*   LISTEN   1050/systemd-resolv
    udp   0   0 127.0.0.53:53   0.0.0.0:*            1050/systemd-resolv


===== - Wireguard =====

https://www.reddit.com/r/WireGuard/comments/1foqw8w/wireguard_issues_relating_to_dns_after_upgrade_to/
https://www.procustodibus.com/blog/2022/03/wireguard-dns-config-for-systemd/

Remove DNS entry from wireguard conf. **Not using WG dns though**

===== - Add DNS Entries =====


===== - Troubleshooting =====
Some domain cannot be resolved  (e.g., google.com but bing.com works). After updating system, may be relink the resolve file:

    sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf


Check which route the DNS query goes:
    ip route get 1.1.1.1
    
    dig google.com @1.1.1.1
    resolvectl query google.com

  * https://unix.stackexchange.com/questions/328131/how-to-troubleshoot-dns-with-systemd-resolved
====== Resources ======
  * https://geekflare.com/linux-server-local-dns-caching/