Private Address Ranges

To provide flexibility in addressing and to prevent an incorrectly configured network from polluting the Internet, certain address ranges are set aside for private use. These address ranges are called private ranges because they are designated for use only on private networks. These addresses are special because Internet routers are configured to ignore any packets they see that use these addresses. This means that if a private network "leaks" onto the Internet, it won't make it any farther than the first router it encounters.

Three ranges are defined in RFC 1918one each from Classes A, B, and C. You can use whichever range you want, although the Class A and Class B address ranges offer more addressing options than does Class C. The address ranges are defined in Table 4.

Table 4 Private Address Ranges


Address Range

Default Subnet Mask