ns1.impsat.net.ar has one IP number , which also has a corresponding reverse pointer. rima.org, kofba.com, impsat.com, ccu.com.ar, impsat.net and at least 100 other hosts use this as a nameserver. impsat.net.ar is a domain controlled by two nameservers at impsat.net.ar themselves. They are on different IP networks. Incoming mail for impsat.net.ar is handled by one mailserver having a total of two IP numbers. They are on the same IP network. ns1.impsat.net.ar is hosted on a server in Argentina.