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ns3.register.bg has one IP number. bg use this as a nameserver. register.bg is a domain controlled by two nameservers at digsys.bg. They are on different IP networks. Incoming mail for register.bg is handled by three mailservers also at digsys.bg. Two of them are on the same IP network. ns3.register.bg is hosted on a server in Bulgaria.

ns3.register.bg
a records
 
+ 94.155.14.10 94.155.0.0/16 AS9070  
+ ---  

register.bg
ns-soa records
ns.digsys.bg
+ 192.92.129.1 192.92.129.0/24 AS3245 -
+ --- -
ns records
ns.digsys.bg
+ 192.92.129.1 192.92.129.0/24 AS3245 -
+ --- -
ns2.digsys.bg
+ 193.68.3.252 193.68.0.0/19 AS3245 -
mx records
relay2.digsys.bg
+ 192.92.129.9 192.92.129.0/24 AS3245 varna.digsys.bg
+ --- varna.digsys.bg
ns.digsys.bg
+ 192.92.129.1 192.92.129.0/24 AS3245 -
+ --- -
relay.digsys.bg
+ 193.68.3.229 193.68.0.0/19 AS3245 -
ip numbers of host
94.155.14.10
domains using this as nameserver
bg