Private IP addresses As Internet use has increased, more and more IP addresses have been assigned. There is not an infinite number of IP addresses, and IANA is concerned that the supply of unique IP addresses could be exhausted. One way to conserve IP addresses is to assign them only to hosts that are designated as "public." Hosts that are designated as "private" do not need unique IP addresses.
Types of hosts IANA has created three categories of hosts:
Category 1: hosts that do not require access to hosts in other enterprises or the Internet at large; hosts within this category may use IP addresses that are unambiguous within an enterprise, but may be ambiguous between enterprises. Category 2: hosts that need access to a limited set of outside services (e.g.,
Hosts in categories 1 and 2 are private hosts. Hosts in Category 3 are public hosts. Hosts in categories 1 and 2 do not need to be directly accessible from other networks. These hosts might include airport arrival/departure displays, automatic teller machines, or equipment at clerical positions. Thus, these private hosts do not need unique IP address numbers. The IP addresses private hosts are assigned need only be unique within the network; they need not be directly accessible from other networks.
In addition, for security reasons, many enterprises use application layer gateways to connect their internal network to the Internet. The internal network usually does not have direct access to the Internet; thus, only one or more gateways are visible from the Internet. In this case, the internal network can use
In short, there are many devices that can be connected on an internal Internet or intranet that need never be assigned unique IP addresses. In this way, IP addresses are conserved.
Private address space IANA has reserved the following three blocks of the IP address space for private internets:
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