TCP/IP Network Administration, 3rd Edition

Chapter 12. Network Security

Hosts attached to a network—particularly the worldwide Internet—are exposed to a wider range of security threats than are unconnected hosts. Network security reduces the risks of connecting to a network. But by nature, network access and computer security work at cross-purposes. A network is a data highway designed to increase access to computer systems, while security is designed to control access to those systems. Providing network security is a balancing act between open access and security.

The highway analogy is very appropriate. Like a highway, the network provides equal access for all—welcome visitors as well as unwelcome intruders. At home, you provide security for your possessions by locking your house, not by blocking the streets. Likewise, network security requires adequate security on individual host computers. Simply securing the network with a firewall is not enough.

In very small towns where people know each other, doors are often left unlocked. But in big cities, doors have deadbolts and chains. The Internet has grown from a small town of a few thousand users into a big city of millions of users. Just as the anonymity of a big city turns neighbors into strangers, the growth of the Internet has reduced the level of trust between network neighbors. The ever-increasing need for computer security is an unfortunate side effect. Growth, however, is not all bad. In the same way that a big city offers more choices and more services, the expanded ...