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. 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 generally means providing adequate security on individual host computers, not providing security directly on the network.

In very small towns, where people know each other, doors are often left unlocked. But in big cities, doors have deadbolts and chains. In the last decade, the Internet has grown from a small town of a few thousand users to 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 network provides increased services. For most of us, security consciousness is a small price to pay for network access.

Network break-ins have increased as the network has grown and become more impersonal, but it is easy to exaggerate the extent of these security breaches. Over-reacting to the threat of break-ins may hinder the way you use the network. Don't make the cure worse than the disease. The best advice about network security is to use common sense. RFC 1244, Site Security Handbook, by Holbrook, Reynold, et al., states this principle very well:

Common sense is the most appropriate tool that can be used to establish your security policy. Elaborate security schemes and mechanisms are impressive, and they do have their place, yet there is little point in investing money and time on an elaborate implementation scheme if the simple controls are forgotten.

This chapter emphasizes the simple controls that can be used to increase your network's security. A reasonable approach to security, based on the level of security required by your system, is the most cost-effective - both in terms of actual expense and in terms of productivity.

1 Security Planning

One of the most important network security tasks, and probably one of the least enjoyable, is developing a network security policy. Most computer people want a technical solution to every problem. We want to find a program that "fixes" the network security problem. Few of us want to write a paper on network security policies and procedures. However, a well-thought-out security plan will help you decide what needs to be protected, how much you are willing to invest in protecting it, and who will be responsible for carrying out the steps to protect it.