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Private IP addresses
Before going into the details, if you are just looking for IP addresses for a small private network, either not connected to the Internet or connected to the Internet through a router with NAT (Network Address Translation), first try to set your IP address and DNS settings to automatic on all computers. This should work in most cases. If the router has a DHCP server, which most WAN (Wide Area Network) routers do, then the computers will obtain valid private IP addresses from the router. If there is no Internet connection, the computers will automatically assume APIPA (Automatic Private IP Address) addresses (169.254..., see below for details if you're interested).
If you need fixed IP addresses and the choice doesn't matter, use Class C addresses from only one of the following three ranges. These are most common in private networks.
If this is not enough, please read on.
This article is a brief summary of RFC-1918 (formerly RFC-1597): "Address Allocation for Private Internets". These are the recommended IP address ranges one can use for hosts that do not require direct access to the Internet. These addresses are filtered by Internet Routers and therefore do not have to be globally unique.
These addresses can be used with out fear of duplicating a unique IP address owned by another enterprise. If globally unique Internet addresses are required, contact your Internet Service Provider or the NIC (Network Information Center) at Hostmaster@NIC.DDN.MIL.
Detailed Information on Private Address Space
The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private networks. Note that the first block is nothing but a single class A network number, while the second block is a set of 16 contiguous class B network numbers, and third block is a set of 255 contiguous class C network numbers.
Addition from outside the RFC: A link local Class B space is the APIPA (Automatic Private IP Address) range:
This range is used, for example, by Windows computers if their IP addresses are set to automatic, but no DHCP server is present.
The range is not a reserved private IP address space, but is often used as one. RFC-3927 says:
See also this Microsoft Knowledge Base article:
Related Additional Information
For a private domain name use
Thus an example for a complete private computer host name could be:
Authoritative sources can be found here:
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