The following key points summarize the operation and benefits of public and private addressing:
• A device directly connected to the Internet has a public IP address. This address is routable. Other devices on the Internet can identify, locate, and request services from a device with a public IP address.
• The number of public IP addresses is limited, so RFC 1918 reserves Class A, B, and C networks for private use on an internal network. These address ranges can be reused for multiple internal networks because the networks are not visible to the Internet or each other.
• A router running NAT and PAT can allow devices on a private network to share a single public IP address and communicate over the Internet.