Originally Posted by till
Your server is unable to resolve the IP addresses for domain names.
Please check your /etc/resolv.conf if the nameservers listed there are working and reachable from your server.
thanks for your reply.
Apt-get works already now.
One more question:
In ISPConfig > Management > Server > Settings > DNS,
i have to mention two DNS-servers:
Default Ns1: ?
Default Ns2: ?
Which DNS-servers have i have to mentioned here,
the IP-address of my own server, which runs Bind9 or
the DNS-resolvers provided by the network of the colocation?