Zyxel-communications 70 Series Manual de usuario descargar pdf (Pagina 204)

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ZyWALL 5/35/70 Series User’s Guide

Chapter 10 Firewalls 204

Figure 89 ZyWALL Firewall Application

10.4 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 ZyWALL is pre-configured to automatically

detect and thwart all known DoS attacks.

10.4.1 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. An extension

number, called the "TCP port" or "UDP port" identifies these protocols, such as HTTP (Web),

FTP (File Transfer Protocol), POP3 (E-mail), etc. 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 information requests 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:

Table 63 Common IP Ports

21 FTP 53 DNS

23 Te l n e t 80 HTTP

25 SMTP 110 POP3

1 2 ... 199 200 201 202 203 204 205 206 207 208 209 ... 806 807

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