24 May 2011

Private IP address ranges and the APIPA

Certain IP address ranges have been reserved for private network use.  These are listed in RFC 1918 http://tools.ietf.org/html/rfc1918.  These ranges can safely be used for internal networks.

Microsoft has also allocated a block of addresses called the Automatic Private IP Addressing (APIPA)  These are used by machines when no IP has been allocated and DHCP is not available. These auto allocted IPs are tomporary and will be superced as soon as a DHCP address becomes available.  http://support.microsoft.com/kb/220874

Range Start

Range End

of hosts




16 777 216

24-bit block

1 048 576

20-bit block

65 536

16-bit block

65 536


When building lab or setting up new environments use the table as a guide to pick Which black or IPs or even part of the block that you want to use.  Bearing in mind that the some of address may already be route-able in your private network.

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