$ host www.bundesnetzagentur.de
Host www.bundesnetzagentur.de not found: 3(NXDOMAIN)

$ gwhois bundesnetzagentur.de | grep Nserver
Nserver:     dns.regtp.de
Nserver:     dns2.regtp.de
Nserver:     ns1.de.colt.net

$ host -t NS bundesnetzagentur.de. ns1.de.colt.net
Using domain server:
Name: ns1.de.colt.net
Address: 212.74.77.55#53
Aliases: 

Host bundesnetzagentur.de not found: 5(REFUSED)

$ gwhois regtp.de | grep Nserver
Nserver:     dns.regtp.de 217.111.27.1
Nserver:     ns1.de.colt.net

$ host dns.regtp.de. 217.111.27.1
Using domain server:
Name: 217.111.27.1
Address: 217.111.27.1#53
Aliases: 

Host dns.regtp.de. not found: 3(NXDOMAIN)

$ host dns2.regtp.de. 217.111.27.1
Using domain server:
Name: 217.111.27.1
Address: 217.111.27.1#53
Aliases: 

Host dns2.regtp.de. not found: 3(NXDOMAIN)

$ host -t NS regtp.de. 217.111.27.1
Using domain server:
Name: 217.111.27.1
Address: 217.111.27.1#53
Aliases: 

regtp.de name server ns1.de.colt.net.
regtp.de name server dns1.bundesnetzagentur.de.
regtp.de name server dns2.bundesnetzagentur.de.

$ host dns.regtp.de. ns1.de.colt.net
Using domain server:
Name: ns1.de.colt.net
Address: 212.74.77.55#53
Aliases: 

Host dns.regtp.de not found: 5(REFUSED)

$ host dns2.regtp.de. ns1.de.colt.net
Using domain server:
Name: ns1.de.colt.net
Address: 212.74.77.55#53
Aliases: 

Host dns2.regtp.de not found: 5(REFUSED)

$ host -t NS regtp.de. ns1.de.colt.net
Using domain server:
Name: ns1.de.colt.net
Address: 212.74.77.55#53
Aliases: 
Host regtp.de not found: 5(REFUSED)

Und jetzt?