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Valid IP Addressing for a Private Network

This article was previously published under Q142863
This article is a brief summary of RFC 1918 Address Allocation for PrivateInternets. These are the recommended IP address ranges one can use forhosts that do not require direct access to the Internet. These addressesare filtered by Internet Routers and therefore do not have to be globallyunique.

These addresses can be used without fear of duplicating a unique IP addressowned by another enterprise. If globally unique Internet addresses arerequired, contact your Internet Service Provider or the NIC (NetworkInformation Center) at Hostmaster@NIC.DDN.MIL.
Private Address Space

The Internet Assigned Numbers Authority (IANA) has reserved the followingthree 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. Thecomplete RFC 1918 can be found via FTP on

For information about obtaining an RFC document, please see the followingarticle in the Microsoft Knowledge Base:
185262 How to Obtain Request for Comments Documents from the Internet
prodnt 2.10 2.20c 3.10 3.11 3.11a 3.50 HIS 2000

Article ID: 142863 - Last Review: 02/12/2010 03:55:51 - Revision: 6.0

  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional Edition
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows 95
  • Microsoft LAN Manager 2.2c
  • Microsoft TCP/IP for Windows for Workgroups 3.11a
  • Microsoft Windows for Workgroups 3.11
  • kbinfo KB142863