TABLE OF CONTENTS The Internet is a collection of networks, both public and private. The private networks include the local area networks (LANs) and wide area networks (WANs) of various institutions, corporations, businesses, and government agencies. The public networks include those of the numerous Internet service providers (ISPs). Although the private networks may communicate internallyusing various communications protocols, the public networks communicate using the Internet Protocol (IP). In order for one private network to communicate with another via a public network, then each private network must have a gateway to the public network and that gateway must speak the language of that network-IP.
We illustrate this situation in Figure 2-1, where a number of private networks are shown, connected to a number of routers. The various entities within a given private network may communicate internally in any way they want, but when communicating with other networks via the Internet, they do so with IP. Routers provide the connectivity between various networks and form the backbone of the Internet.
The foregoing does not mean to imply that private networks like LANs and WANs do not use IP. The vast majority of them do. The reasons are numerous, including the fact that IP is embraced by all major developers of computer systems, and it supports a vast array of applications. Moreover, compared to some other types of networks, it can be relatively easy to implement an IP-based network.
IP and some of the related protocols would...
