In Internet networking, a private network is a

computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections ar ...

that uses a private

address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve ...

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

es. These addresses are commonly used for

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...

s (LANs) in residential, office, and enterprise environments. Both the

IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version d ...

and the

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. I ...

specifications define private IP address ranges. Private network addresses are not allocated to any specific organization. Anyone may use these addresses without approval from regional or local Internet registries. Private IP address spaces were originally defined to assist in delaying

IPv4 address exhaustion IPv4 address exhaustion is the depletion of the pool of unallocated IPv4 addresses. Because the original Internet architecture had fewer than 4.3 billion addresses available, depletion has been anticipated since the late 1980s, when the Intern ...

. IP packets originating from or addressed to a private IP address cannot be routed through the public

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''internetworking, network of networks'' that consists ...

Private IPv4 addresses

The

Internet Engineering Task Force The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and ...

(IETF) has directed the

Internet Assigned Numbers Authority The Internet Assigned Numbers Authority (IANA) is a standards organization that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System (DNS), media types, and other Internet ...

(IANA) to reserve the following IPv4 address ranges for private networks: In practice, it is common to subdivide these ranges into smaller subnets.

Dedicated space for carrier-grade NAT deployment

In April 2012, IANA allocated the block ''100.64.0.0/10'' (100.64.0.0 to 100.127.255.255, netmask 255.192.0.0) for use in carrier-grade NAT scenarios. This address block should not be used on private networks or on the public Internet. The size of the address block (2²², approximately 4 million addresses) was selected to be large enough to uniquely number all customer access devices for all of a single operator's

points of presence A point of presence (PoP) is an artificial demarcation point or network interface point between communicating entities. A common example is an ISP point of presence, the local access point that allows users to connect to the Internet with their ...

in a large metropolitan area such as

Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and List of cities in Japan, largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, ...

Private IPv6 addresses

The concept of private networks has been extended in the next generation of the

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

, and special address blocks are reserved. The address block is reserved by IANA for Unique Local Addresses (ULA). They are

unicast Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication. In computer networking, unicast is a one-to-one transmission from one point in ...

addresses, but contain a 40-bit random number in the routing prefix to prevent collisions when two private networks are interconnected. Despite being inherently ''local'' in usage, the IPv6 address scope of unique local addresses is global. The first block defined is , designed for /48 routing blocks, in which users can create multiple subnets, as needed. Examples: A former standard proposed the use of ''site-local'' addresses in the block, but because of scalability concerns and poor definition of what constitutes a ''site'', its use has been deprecated since September 2004.

Link-local addresses

Another type of private networking uses the link-local address range. The validity of link-local addresses is limited to a single link; e.g. to all computers connected to a

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type ...

, or to one

wireless network A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing c ...

. Hosts on different sides of a

network bridge A network bridge is a computer networking device that creates a single, aggregate network from multiple communication networks or network segments. This function is called network bridging. Bridging is distinct from routing. Routing allows ...

are also on the same link, whereas hosts on different sides of a

network router A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions between networks and on the global Internet. Data sent through a network, such as a web page or email, is ...

are on different links.

IPv4

In IPv4, link-local addresses are codified in RFC 6890 and RFC 3927. Their utility is in

zero-configuration networking Zero-configuration networking (zeroconf) is a set of technologies that automatically creates a usable computer network based on the Internet Protocol Suite (TCP/IP) when computers or network peripherals are interconnected. It does not require manu ...

when

Dynamic Host Configuration Protocol The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...

(DHCP) services are not available and manual configuration by a network administrator is not desirable. The block was allocated for this purpose. If a host on an IEEE 802 (

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in ...

) network cannot obtain a network address via DHCP, an address from to may be assigned

pseudorandom A pseudorandom sequence of numbers is one that appears to be statistically random, despite having been produced by a completely deterministic and repeatable process. Background The generation of random numbers has many uses, such as for random ...

ly. The standard prescribes that address collisions must be handled gracefully.

IPv6

In IPv6, the block is reserved for IP address autoconfiguration. Updated by RFC 5952, RFC 6052, RFC 7136, RFC 7346, RFC 7371, RFC 8064. The implementation of these link-local addresses is mandatory, as various functions of the IPv6 protocol depend on them. Updated by RFC 7527.

Loopback interface

A special case of private link-local addresses is the loopback interface. These addresses are private and link-local by definition, since packets never leave the host device. IPv4 reserves the entire class A address block for use as private loopback addresses. IPv6 reserves the single address .

Common uses

Private addresses are commonly used in residential IPv4 networks. Most

Internet service provider An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise privatel ...

s (ISPs) allocate only a single publicly routable IPv4 address to each residential customer, but many homes have more than one computer,

smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whic ...

, or other Internet-connected device. In this situation, a network address translator (NAT/PAT) gateway is usually used to provide Internet connectivity to multiple hosts. Private addresses are also commonly used in corporate networks which, for security reasons, are not connected directly to the Internet. Often a proxy,

SOCKS A sock is a piece of clothing worn on the feet and often covering the ankle or some part of the calf. Some types of shoes or boots are typically worn over socks. In ancient times, socks were made from leather or matted animal hair. In the lat ...

gateway, or similar devices are used to provide restricted Internet access to network-internal users. 24-bit block private addresses are also commonly used in the

North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and shares borders with China and Russia to the north, at the Yalu (Amnok) and ...

n Kwangmyong network. In both cases, private addresses are often seen as enhancing

network security Network security consists of the policies, processes and practices adopted to prevent, detect and monitor unauthorized access, misuse, modification, or denial of a computer network and network-accessible resources. Network security involves th ...

for the internal network, since use of private addresses internally makes it difficult for an Internet (external) host to initiate a connection to an internal system.

Misrouting

It is common for packets originating in private address spaces to be misrouted onto the Internet. Private networks often do not properly configure DNS services for addresses used internally and attempt

reverse DNS lookup In computer networks, a reverse DNS lookup or reverse DNS resolution (rDNS) is the querying technique of the Domain Name System (DNS) to determine the domain name associated with an IP address – the reverse of the usual "forward" DNS lookup o ...

s for these addresses, causing extra traffic to the Internet root nameservers. The AS112 project attempted to mitigate this load by providing special ''blackhole''

anycast Anycast is a network addressing and routing methodology in which a single destination IP address is shared by devices (generally servers) in multiple locations. Routers direct packets addressed to this destination to the location nearest the sen ...

nameservers for private address ranges which only return negative result codes (''not found'') for these queries. Organizational edge routers are usually configured to drop ingress IP traffic for these networks, which can occur either by misconfiguration, or from malicious traffic using a spoofed source address. Less commonly, ISP edge routers drop such egress traffic from customers,