CCIE Lab

Foundation Topics

Computer systems are a fundamental component of nearly every organization today. Large and small corporations, government agencies, and other organizations devote significant resources to maintaining their networks, and even the smallest organization is likely to use a computer to maintain its records and financial information. Because these systems can perform functions rapidly and accurately and because they make it easy to facilitate communication between organizations, computer networks continue to grow and become more interconnected. Any organization that wants to provide some public access to its network usually maintains a connection to the Internet. This access does not come without certain risks. This chapter defines some of the risks to networks and explains how an ineffective network security policy can further increase the chance of a network security breach. The key issues in securing and maintaining a computer network are confidentiality, integrity, and availability.

To understand attacks, you must remember that a computer, no matter how advanced, is a machine that operates based on predetermined instruction sets. The operating systems and other software packages are compiled instruction sets that the computer uses to transform input into output. A computer cannot determine the difference between authorized and unauthorized input unless this information is written into the instruction sets. Any point in a software package that enables a user to alter the software or gain access to a system (that was not specifically designed into the software) is called a vulnerability. In many cases, crackers can exploit vulnerabilities and thus gain access to a network or computer. It is possible to remotely connect to a computer on any of 65,535 available ports. As hardware and software technology continues to advance, the "dark side" continues to search for and discover new vulnerabilities. For this reason, most software manufacturers continue to produce patches for their products as vulnerabilities are discovered.