ZyXEL g-2000 plusv2 Guia Do Utilizador
ZyXEL G-2000 Plus v2 User’s Guide
Chapter 10 Firewalls
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Figure 50 ZyXEL device 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 ZyXEL device is pre-configured to
automatically detect and thwart all known DoS attacks.
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.
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.
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.
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 47 Common IP Ports
21
FTP
53
DNS
23
Telnet
80
HTTP
25
SMTP
110
POP3