Lecture 12: IP Networks

Private IP Addresses/Networks

(This is Optional Material)

These are an interesting development in Internetworking. IP addresses have recently become more difficult to obtain, and therefore more expensive. Many organisations (and home users!) have moved to a private address space for their "internal" networks -- ie, networks consisting of machines which do not require globally-valid IP addresses. This has advantages both in terms of cost and security (see later).

RFC1918 specifies a range of addresses: 10.0.0.0,

172.16.0.0 -
172.31.255.255

and

192.168.0.0 -
192.168.255.255

which can be used for this purpose. No IP addresses in these three ranges are ever valid in the Internet (ie, an Internet router should never forward them), and may only be used within private networks.

A variety of technologies are available to allow "internal" (private IP) machines to gain access to services in the outside Internet. The two most common are Network Address Translation (NAT) and SOCKS. For "Web-only" access, an HTTP proxy server can be used.

Lecture 12: IP Networks

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