216.73.217.40

The Internet Protocol address, or IP address, is a unique address that computing devices such as personal computers, tablets, and smartphones use to identify themselves and communicate with other devices on an IP network. Any device connected to an IP network must have a unique IP address within that network. An IP address is similar to a street address or telephone number because it uniquely identifies an entity.

The traditional IP address, known as IPv4, uses a 32-bit number to represent an address and defines both the network and host address. A 32-bit number can provide roughly 4 billion unique addresses, which is why IPv4 addresses have become scarce as more devices connect to the internet. A newer version of the IP protocol, IPv6, was created to offer a much larger address space.

An IPv4 address is written in dotted decimal notation: four sets of numbers separated by periods, with each set representing an 8-bit number ranging from 0 to 255. For example, 216.3.128.12 is an IPv4 address.

An IPv4 address is divided into two parts: the network address and the host address. The network address determines how many of the 32 bits identify the network, while the remaining bits identify the host. The host portion can also be divided into subnet and host numbers.

Traditionally, IP networks were classified as Class A, B, or C networks. Computers identify the class by the first bits of the address, while humans often identify the class by the first octet. With the scarcity of IPv4 addresses, class-based addressing has largely been replaced by Classless Inter-Domain Routing, or CIDR, which allocates address space more efficiently.

Note: the 127.0.0.0/8 network is reserved for loopback testing. Class D addresses, 224-247, are used for multicast, and Class E addresses, 248-255, are experimental and not intended for normal public operation.

To maintain uniqueness across the global internet, public IP addresses are registered so that address conflicts can be avoided. Devices that need to be publicly reachable, such as web servers and mail servers, require globally unique public IP addresses. Devices that do not require direct public access can use private IP addresses that are unique only inside an organization or local network.

For example, a network printer may use a private IP address so it can be reached inside an office without being directly exposed to the internet. To allow organizations to freely assign private addresses, specific address blocks were reserved for private use under RFC 1918.

In addition to the private ranges above, addresses from 169.254.0.0 through 169.254.255.255 are reserved for Zeroconf, also known as APIPA, to automatically create a usable local network when no DHCP configuration is available.

The loopback IP address is used by a device to access itself. IPv4 designates 127.0.0.1 as the loopback address with the 255.0.0.0 subnet mask. A loopback interface is also known as a virtual IP because it is not associated with a physical network interface. On Linux systems, the loopback interface is commonly called lo or lo0, and the corresponding hostname is localhost.

The loopback address is useful for testing network software without installing or connecting a physical network card. A common example is accessing a web server running on the same machine by visiting http://127.0.0.1 or http://localhost.

Do you want to find an IP address of your network printer? Please read How to find an IP of a printer to find ways to obtain an IP number of your network printer.

Do you want to find IP addresses on a private network? Please read How to find IP addresses of computing devices on the private network?