How do I know if an IP address is internal or public?

Question

How do I know if an IP address is internal or public?

Answer

IANA reserved the following ranges for private networks, and therefore, you will never find them on a  public interface:

192.168.0.0 - 192.168.255.255 (65,536 IP addresses)
172.16.0.0 - 172.31.255.255 (1,048,576 IP addresses)
10.0.0.0 - 10.255.255.255 (16,777,216 IP addresses)