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Private IP ranges

Ever wonder what the correct IP addresses are for use internally? Here's a list of the recommended IP address ranges you can use for hosts that don't require direct access to the Internet. These addresses are filtered by Internet Routers and therefore do not have to be globally unique. Also, they can be used without fear of duplicating a unique IP address owned by another company.

The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private networks:

• 10.0.0.0 - 10.255.255.255
• 172.16.0.0 - 172.31.255.255
• 192.168.0.0 - 192.168.255.255

The first block is a single class A network number, 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. You can read more about the private IP ranges in RFC 1918, though as you're probably aware, RFC reading can be a bit dry!