Valid IP Addressing for a Private Network


This article is a brief summary of RFC 1918 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 without 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.

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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 the third block is a set of 255 contiguous class C network numbers. The complete RFC 1918 can be found via FTP on

For information about obtaining an RFC document, please see the following article in the Microsoft Knowledge Base:
185262 How to Obtain Request for Comments Documents from the Internet

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