Private IP address

In the addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 for Version 4 (IPv4), and RFC 4193 for Internet Protocol Version 6 (IPv6). These addresses are commonly used for home, office, and enterprise local area networks (LANs). Private IP address spaces were originally defined in an effort to delay IPv4 address exhaustion, but they are also a feature of IPv6 where exhaustion is not an issue.

Addresses in the private space are not allocated to any specific organization and anyone may use these addresses without approval from a regional Internet registry. However, IP packets addressed from them cannot be transmitted through the public Internet, and so if such a private network needs to connect to the Internet, it must do so via a network address translator (NAT) gateway, or a proxy server.

The Internet Engineering Task Force (IETF) has directed the Internet Assigned Numbers Authority (IANA) to reserve the following IPv4 address ranges for private networks, as published in RFC 1918:

Users can randomly assign networks and subnets from the above ranges, however as the space is relatively small this can create conflicts when merging (see below).

In April 2012, IANA allocated 100.64.0.0/10 for use in carrier-grade NAT scenarios in RFC 6598. This address block should not be used either on private networks or on the public Internet: it is intended only for use within the internal operations of carrier networks. 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 in a large metropolitan area such as Tokyo.

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