ZyXEL Communications P-312 manual Denial of Service, Basics

P312 Broadband Security Gateway

Figure 13-1 Prestige Firewall Application

13.3 Denial of Service

Denials of Service (DoS) attacks are aimed at devices and networks with a connection to the Internet. Their goal is not to steal information, but to disable a device or network so users no longer have access to network resources. The Prestige is pre-configured to automatically detect and thwart all known DoS attacks.

13.3.1 Basics

Computers share information over the Internet using a common language called TCP/IP. TCP/IP, in turn, is a set of application protocols that perform specific functions. These protocols, such as HTTP (Web), FTP (File Transfer Protocol), POP3 (E-mail), etc., are identified by an “extension number”, called the "TCP port" or "UDP port". For example, Web traffic by default uses TCP port 80.

When computers communicate on the Internet, they are using the client/server model, where the server "listens" on a specific TCP/UDP port for requests for information from remote client computers on the network. For example, a Web server typically listens on port 80. Please note that while a computer may be intended for use over a single port, such as Web on port 80, other ports are also active. If the person configuring or managing the computer is not careful, a hacker could attack it over an unprotected port. Some of the most common IP ports are:

What Is a Firewall? 13-3