IP address is short for Internet Protocol address. Every device that connects directly to the Public Internet has a public IP address. Devices in a Private Network ,e.g., corporate network, can use a private IP address to connect to other devices on the Private Network, one of which can be a Private Network Gateway that has a public IP. Private Network devices can then communicate with devices on the Public Internet by routing information to the Private Network Gateway, which uses a Network Address Translation (NAT) to connect a Private Network device with a device on the Public Internet.

Two versions of IP addresses are currently being used:

IPv4 (version 4) is the older version. It has a 32-bit address, with 4 sets of one-to-three-digit numbers (0 to 255) separated by periods, e.g., 232.6.91.147. Although there are over 4 billion IPv4 addresses available, eventually IPv4 will be replaced by longer, more numerous IPv6 addresses.

IPv6 (version 6) has a 128-bit address, with 8 sets of one-to-four hexadecimal numbers (0 to 9 plus A,B,C,D,E,F) separated by colons, e.g., 9688:DB8:0:1234:0:567:0F:1

The longer IPv6 not only supports many more addresses than IPv4 (85 billion billion billion times as many addresses) but also provides better efficiency, performance, and security.

IPv4 and IPv6 are not compatible with each other, although IPv4 can be converted into IPv6. (See 4. NETWORK TOOLS - C - IPv4 to IPv6 below.) Intermediary technology is needed to ensure compatibility and functionality between the two protocols. Currently, IPv4 dominates the public internet space and is widely used for things like server cluster hosting and dedicated servers.

Users generally interact with the Public Internet by visiting websites via a client, e.g., laptop or cell phone. To visit a website, users almost always reference the website domain name, e.g. , Microsoft.com, and not its IP address. Websites are connected to the Public Internet by registering a unique domain name with a domain registrar, which will translate the domain name to the current IP address associated with the domain name.

The domain registrar will have two fields, each pointing to a different Name Server, either the default ones if the domain registrar is to be the host server of the domain name, or the owner can enter two different Name Servers provided by his desired domain host server.

Domain names remain constant, but the IP address associated with the domain name changes whenever the domain host server changes.

A typical transaction is for a client to request information from a website/domain name server. Just as every website on the Public Internet must have an associated IP address, every client must also have an associated IP address in order to receive information back from a website.

A client IP address is generally created by the client's server at the time the client logs onto its server, e.g., wifi or cell phone network. This IP address will obviously change with different client servers. The IP address can also change even if same client server is always used because most IP address assignments are based on the number of other clients using that server.