go
ns4.nic.co has one IP number , which also has a corresponding reverse pointer. ns3.bk.bna-net.jp point to the same IP. co use this as a nameserver. ns4.nic.co is hosted on a server in United States even though the hostname implies Colombia.

ns4.nic.co
a records
 
+ 128.121.234.109 128.121.0.0/16 AS2914 -
+ --- -
ip numbers of host
128.121.234.109
ptrs of ip numbers
ns4.nic.co
ip numbers using ptr to this host
128.121.234.109
hostnames sharing ip with a-records
ns3.bk.bna-net.jp
domains using this as nameserver
co