In Internet terminology, a private network is a network that uses private IP address space, following the agreed standard of RFC 1918. Computers may be allocated addresses from this address space when it is necessary for them to communicate with other computing devices on an internal (non-Internet) network. An IP address (or Internet Protocol address) is a unique address that certain electronic devices use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard (IP)—in simpler terms, a computer address. ...

Private networks are quite common in home and office local area network (LAN) designs, as many organizations do not see a need for globally unique IP addresses for every computer, printer and other device that the organizations use. Another reason for the extensive use of private IP addresses is the shortage of publicly registered IP addresses. IPv6 was created to alleviate this shortage, but has yet to achieve widespread use. LAN redirects here. ... SGI O2 Workstation A computer workstation, often colloquially referred to as workstation, is a high-end general-purpose microcomputer designed to be used by one person at a time and which offers higher performance than normally found in a personal computer, especially with respect to graphics, processing power and the... A computer printer, or more commonly a printer, produces a hard copy (permanent human-readable text and/or graphics) of documents stored in electronic form, usually on physical print media such as paper or transparencies. ... Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ...

Routers on the Internet are (normally) configured to discard any traffic using private IP addresses. This isolation gives private networks a basic form of security as it is not usually possible for the outside world to establish a connection directly to a machine using these addresses. As connections cannot be made between different private networks via the internet, different organizations can use the same private address range without risking address conflicts (communications accidentally reaching third party which is using the same IP address). This article is about a computer networking device. ...

If a device on a private network needs to communicate with other networks, a "mediating gateway" is needed to ensure that the outside network is presented with an address that is "real" (or publicly reachable) so that routers allow the communication. This gateway is typically a network address translation (NAT) device or a proxy server. This article is about a computer networking device. ... In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets... In computer networks, a proxy server is a server (a computer system or an application program) which services the requests of its clients by forwarding requests to other servers. ...

This can cause problems, however, when organizations try to connect networks that both use private address spaces. There is the potential for clashes and routing problems if both networks use the same IP addresses for their private networks, or rely on NAT to connect them through the Internet.

The current IANA private internet addresses are: The Internet Assigned Numbers Authority (IANA) is the entity that oversees global IP address allocation, DNS root zone management, and other Internet protocol assignments. ...

To reduce load on the root nameservers caused by reverse DNS lookups for these IP addresses, a system of "black-hole" nameservers are provided by anycast network AS112. [1] Classful networking is the name given to the first round of changes to the structure of the IP address in IPv4. ... Warning! This Article contains disinformation. ... The AMS-IX mirror of the K root-server. ... Reverse DNS lookup (rDNS) is a process to determine the hostname or host associated with a given IP address or host address. ... Routing Schemes anycast broadcast multicast unicast Anycast is a network addressing and routing scheme whereby data is routed to the nearest or best destination as viewed by the routing topology. ... In the Internet, an autonomous system (AS) is a collection of IP networks and routers under the control of one entity (or sometimes more) that presents a common routing policy to the Internet. ...

Link-local addresses (Zeroconf)

A second set of private networks is the link-local address range codified in RFC 3330 and RFC 3927. The intention behind these RFCs is to provide an IP address (and by implication, network connectivity) without a DHCP server being available and without having to configure a network address manually. The network 169.254/16 has been reserved for this purpose. Within this address range, the networks 169.254.0/24 and 169.254.255/24 have been set aside for future use. Zeroconf or Zero Configuration Networking is a set of techniques that automatically create a usable IP network without configuration or special servers. ... DHCP redirects here. ...

If a host on an IEEE 802 (ethernet) network cannot obtain a network address via DHCP, an address from 169.254.1.0 to 169.254.254.255 is assigned pseudorandomly. The standard prescribes that address collisions must be handled gracefully. Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... A pseudo-random number is a number belonging to a sequence which appears to be random, but can in fact be generated by a finite computation. ...

Link-local addresses have even more restrictive rules than the private network addresses defined in RFC 1918: packets to or from link-local addresses must not be allowed to pass through a router at all (RFC 3927, section 7).

Private networks and IPv6

IPv6 does not include private network features such as NAT. Because of the very large number of IPv6 addresses (the IPv6 address space is 128 bits compared to 32 bits for IPv4), IPv6 users should be able to obtain IPv6 address space for use at their discretion and without artificial barriers between their network and the Internet. However, there is an address range allocated for cases where users will not be able to get an officially assigned network, namely the fc00::/7 range as described in RFC 4193. Addresses from this range are called "Unique Unicast", since each network contains a 40 bit random number to prevent collisions when two private networks are interconnected. Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ...

A former standard proposed the use of so-called "site-local" addresses in the fec0::/10 range, but due to major concerns about scalability and the extremely fuzzy definition of "site", its use has been deprecated since September 2004 in RFC 3879.

IANA Reserved Addresses

The IANA has reserved several address ranges, including 1.0.0.0 - 2.255.255.255^[1]. In recent years, large companies have begun to use this address space internally; though discouraged, it appears to have become an accepted practice among larger companies to use these reserved address spaces when connecting two private networks, to eliminate any chance of address conflicts.

Fonality uses both 1.0.30.1/24 and 2.0.30.1/24 to establish a tunnel between their PBX's and their servers. Data Return (now Terremark) uses 1.4.0.0/16 for their internal network.^{[citation needed]} Hamachi uses 5.0.0.0/8 within their VPN service over UDP (they only use that address for the VPN Service and not transport across routers, 5.0.0.0/8 is not routable across any internet router). Meraki uses 5.0.0.0/8 and 6.0.0.0/8 with their mesh routers. This article is about the computer networking software. ...

External links

• RFC 1918 – "Address Allocation for Private Internets"
• RFC 3879 – "Deprecating Site Local Addresses"
• RFC 3927 – "Dynamic Configuration of IPv4 Link-Local Addresses"
• RFC 4193 – "Unique Local IPv6 Unicast Addresses"
• Generator for RFC 4193 Addresses (source code available from same page)

References

1. ^ Internet Protocol v4 Address Space