What Are Internal Names ?

Internal names include hosts and domains that cannot be registered or resolved in public DNS e.g., server01 or server.local, localhost, etc.

Internal IP addresses cannot be registered for use on public networks. They include IPv4 or IPv6 addresses the Internet Assigned Numbers Authority (IANA) marks as reserved. The most common reserved ranges are 10.0.0.0-10.255.255.255, 172.16.0.0-172.31.255.255, and 192.168.0.0 - 192.168.255.255. More information is available here.