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systemdoctor.com use this as a nameserver. systemdoctor.com is delegated to four nameservers, however all four delegated nameservers are missing in the zone. All nameservers are at systemdoctor.com themselves. Two nameservers have the same IP number. Two of them are on the same IP network.

systemdoctor.com
ns records
ns1.systemdoctor.com
+ 208.79.82.50 208.79.80.0/22 AS13647  
+ ---  
ns2.systemdoctor.com
+   AS?  
ns3.systemdoctor.com
+   AS?  
ns4.systemdoctor.com
+ 77.73.98.4 77.73.96.0/22 AS39318 77-73-98-4.ant.nucleus.be
+ --- 77-73-98-4.ant.nucleus.be
domains using this as nameserver
systemdoctor.com
nameservers missing in zone
ns1.systemdoctor.com
ns2.systemdoctor.com
ns3.systemdoctor.com
ns4.systemdoctor.com
used as nameserver but missing in zone
systemdoctor.com