Our local network has internal domains that end on .int. When running Ubuntu 18.04.1 LTS as guest in VirtualBox running on a Windows 10 host, it randomly looses the ability to resolve those domains.

When this happens, neither ping nor a browser are able to reach a server through an internal .int domain, but by querying the IP. Only restarting the virtual machine enables the resolving of .int domains again. External domains that end on a regular top-level domain can be resolved at all times.

So far, I have tried the following steps:

  • sudo service network-manager restart
  • disconnect and reconnect the virtual cable connection to the virtual machine
  • sudo systemd-resolve --flush-caches
  • resolve one of our .int domains using nslookup with --dns-ip= to force using our internal DNS server for resolving

All of this did not lead to an internal .int domain being resolved. Only rebooting the Ubuntu guest in VirtualBox allows to resolve the internal domains again.

While resolving of internal domains is broken, nmcli device show [device] shows that the internal DNS server is still listed as IP4.DNS[1] and responds to a ping.

Any hints on how to further examine and solve this problem would be appreciated.

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