In Internet terminology, a private network is a network that uses RFC 1918 IP address space and is not connected to the public Internet. Private networks are available for any use by anyone and therefore the same private IP addresses can be reused.

Private networks are becoming quite common in office LAN (LAN) designs, as many organizations do not see a need for globally unique IP addresses for every computer workstation, computer printer and other device that the organizations use. Another reason for the extensive use of private IP addresses is the shortage of publicly registerable IP addresses. IPv6 was created to alleviate this shortage, but is yet to be in widespread use.

Private IP addresses also provide a basic form of security as in a typical network configuration of this type it is not possible for the outside world (Internet) to establish a connection directly to a host using these addresses.

NAT (NAT) devices are required to connect private networks to the Internet. The NAT device will have at least one real or publicly-reachable address, and will route traffic destined for the public Internet through that address. This can cause problems, however, when organizations try to connect two networks that both use private address spaces. There is the potential for clashes and routing problems if both networks use the same IPs for their private networks, or rely on NAT to connect them through the Internet.

Specifically, the networks are:

RFC 1597 was the original specification but is now for historical purposes only.

To reduce load on the root nameservers caused by reverse DNS lookups for these IP addresses, a system of black-hole nameservers is provided by Anycast network autonomous system (Internet)112. [http://www.as112.net/]

=Bit-wise representation=

... start @ 10 0. 0. 0 = 00001010.00000000.00000000.00000000 (private subnet mask) finish @ 10.255.255.255 = 00001010.11111111.11111111.11111111 (prv b/cast address*) 00001010.XXXXXXXX.XXXXXXXX.XXXXXXXX (private 24 bit block) ... start @ 172. 16. 0. 0 = 10101100.00010000.00000000.00000000 (private subnet mask) finish @ 172. 31.255.255 = 10101100.00011111.11111111.11111111 (prv b/cast address*) 10101100.0001XXXX.XXXXXXXX.XXXXXXXX (private 20 bit block) ... start @ 192.168. 0. 0 = 11000000.10101000.00000000.00000000 (private subnet mask) finish @ 192.168.255.255 = 11000000.10101000.11111111.11111111 (prv b/cast address*) 11000000.10101000.XXXXXXXX.XXXXXXXX (private 16 bit block) ...

=See also=

=External links=