Ubuntu - VPN - ExpressVPN - Revert to internal DNS upon ExressVPN disconnect

ExpressVPN has a bug in that it does not revert the /etc/resolv.conf DNS settings back to the internal one when the VPN is disonnected.

This results in internet queries still trying to use the ExpressVPN DNS, which is cannot access due to the VPN being off.

Disconnect from ExpressVPN

expressvpn disconnect

Check which DNS server is being used

systemd-resolve --status

returns:

Global
       LLMNR setting: no
MulticastDNS setting: no
  DNSOverTLS setting: no
      DNSSEC setting: no
    DNSSEC supported: no
  Current DNS Server: 10.100.0.1
         DNS Servers: 10.100.0.1
          DNS Domain: expressvpn

NOTE: The Current DNS Server line should be pointing to the internal DNS, but here it shows this still points to the ExpressVPN DNS even though the VPN is disconnected.

Fix this issue

Check the status of the systemd-resolv service

sudo systemctl status systemd-resolved.service

returns:

● systemd-resolved.service - Network Name Resolution
     Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2022-03-17 19:28:19 GMT; 4 days ago
       Docs: man:systemd-resolved.service(8)
             https://www.freedesktop.org/wiki/Software/systemd/resolved
             https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
             https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
   Main PID: 1160 (systemd-resolve)
     Status: "Processing requests..."
      Tasks: 1 (limit: 77016)
     Memory: 7.6M
     CGroup: /system.slice/systemd-resolved.service
             └─1160 /lib/systemd/systemd-resolved
 
Mar 17 19:28:19 bigmamba systemd[1]: Starting Network Name Resolution...
Mar 17 19:28:19 bigmamba systemd-resolved[1160]: Positive Trust Anchors:
Mar 17 19:28:19 bigmamba systemd-resolved[1160]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Mar 17 19:28:19 bigmamba systemd-resolved[1160]: Negative trust anchors: 10.in-addr.arpa 16.172.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.172.in-addr.arpa 21.172.in-addr.arpa 22.172.in-addr.arpa 23.172.in-addr.arpa 24.172.in-addr.arpa 25.172.in-addr.arpa 26.172.in-addr.arpa 27.172.in-addr.arpa 28.172.in-addr.arpa 29.172.in-addr.arpa 30.172.in->
Mar 17 19:28:19 bigmamba systemd-resolved[1160]: Using system hostname 'bigmamba'.
Mar 17 19:28:19 bigmamba systemd[1]: Started Network Name Resolution.
Mar 17 19:30:37 bigmamba systemd-resolved[1160]: Flushed all caches.
Mar 20 10:47:01 bigmamba systemd-resolved[1160]: Flushed all caches.

NOTE: This shows the service is running. Good.

Restart the systemd-resolv service

sudo systemctl restart systemd-resolved.service

Check again which DNS server is being used

systemd-resolve --status

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