RFC 1918 - Address Allocation for Private Internets

Status of this Memo
This document specifies an Internet Best Current Practices for the    Internet Community, and requests discussion and suggestions for    improvements.  Distribution of this memo is unlimited.
1. Introduction
For the purposes of this document, an enterprise is an entity    autonomously operating a network using TCP/IP and in particular    determining the addressing plan and address assignments within that    network.
This document describes address allocation for private internets. The    allocation permits full network layer connectivity among all hosts    inside an enterprise as well as among all public hosts of different    enterprises. The cost of using private internet address space is the    potentially costly effort to renumber hosts and networks between    public and private.

Private Address Space

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

• 10.0.0.0        -   10.255.255.255  (10/8 prefix)
• 172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
• 192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

Quelle: tools.ietf.org/html/rfc1918