Private IP Addresses
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Some TCP/IP networks are set up with the intent that they will never be connected to the
global Internet. This type of network is usually referred to as a Private Network.
Some private networks are set up for security reasons, and others simply because
their purpose does not require global Internet connectivity. For example, bank networks or
corporate networks carrying confidential information may not be connected to the Internet
for security reasons. Airport networks that display arrival and departure information, or
networks that serve cash registers in stores do not necessarily need Internet connectivity.
Because of concerns over the growing shortage of IP addresses, there is a special set of IP addresses that have been set aside by the Internet Assigned Numbers Authority (IANA) for private networks. These addresses will not be assigned to any system connected to the global Internet. There are three blocks of private IP addresses:
Private IP addresses are sometimes referred to as Non-Routable IP. This is because the addresses are not routed to the Internet by an Internet Service Provider. The name is misleading since these networks can be routed by standard routing equipment within private networks and Intranets. Network administrators often use private IP addresses when setting up firewall security systems. The systems inside some firewalls are not directly accessible from the Internet and only communicate by proxy, they can use private IP addresses. This is partly a security measure since the addresses will not be routed across the Internet, and partly a measure to conserve IP addresses. Private IP addresses are documented in RFC 1597.
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