The IANA has reserved a block of IPv4 addresses. These private addresses are used for network traffic within a private network. Organizations that request a block of IPv4 addresses from their Internet Service Provider are unlikely to receive a sufficient allocation to have unique address for each of their systems. Organizations typically assign private addresses to the systems on their internal networks. Their systems can effectively share the limited Internet Service Provider (ISP) provided addresses by using Network Address Translators (NAT) and application proxy servers to communicate with other sites on the Internet.
The following table lists the private IPv4 address ranges and their corresponding netmask.