ZyXEL Communications P-324 User's Guide download pdf (Page 201)

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P-2602HWNLI User’s Guide

Chapter 13 Firewalls 201

• The LAN (Local Area Network) port attaches to a network of computers, which needs

security from the outside world. These computers will have access to Internet services

such as e-mail, FTP, and the World Wide Web. However, “inbound access” will not be

allowed unless you configure remote management or create a firewall rule to allow a

remote host to use a specific service.

13.3.1 Denial of Service Attacks

Figure 104 Firewall Application

13.4 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 ZyXEL Device is pre-configured to

automatically detect and thwart all known DoS attacks.

13.4.1 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.

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