ns5.us.dell.com has one IP number , which also has a corresponding reverse pointer. dell.se, dell.de, dell.nl, dell.dk, dell.com and at least 100 other hosts use this as a nameserver. us.dell.com is a domain controlled by five nameservers at us.dell.com themselves. All of them are on the same IP network. Incoming mail for us.dell.com is handled by one mailserver having a total of two IP numbers. They are on the same IP network. us.dell.com has one IP number , but the reverse is ns1.us.dell.com. ns5.us.dell.com is hosted on a server in United States.