release upgrade breaks internet and other things

[Volker Wysk]

Hi

I've done a do-release-upgrade on my 16.04 LTS system. This has broken  
the internet connection, and more. I get immediate "unknown host"  
errors when I ping to any host. When I lookup an adress in Firefox, I  
get a "Page not found, The connection to the server ... failed."

Sorry, I don't know how to troubleshoot this connection problem.

Where should I look..?

Should i even look, or would it be easier to reinstall everything in a  
new 18.04.1 system from scratch? (This would be quite a few things.)

Thanks
Volker