ZyXEL Prestige 660HW-D1 Wireless Router 91-004-593003B Manual Do Utilizador

P-660H/HW-D Series User’s Guide

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Chapter 9 Firewalls

Application-level firewalls restrict access by serving as proxies for external servers. Since they 
use programs written for specific Internet services, such as HTTP, FTP and telnet, they can 
evaluate network packets for valid application-specific data. Application-level gateways have 
a number of general advantages over the default mode of permitting application traffic directly 
to internal hosts:

Information hiding prevents the names of internal systems from being made known via DNS 
to outside systems, since the application gateway is the only host whose name must be made 
known to outside systems.

Robust authentication and logging pre-authenticates application traffic before it reaches 
internal hosts and causes it to be logged more effectively than if it were logged with standard 
host logging. Filtering rules at the packet filtering router can be less complex than they would 
be if the router needed to filter application traffic and direct it to a number of specific systems. 
The router need only allow application traffic destined for the application gateway and reject 
the rest.

Stateful inspection firewalls restrict access by screening data packets against defined access 
rules. They make access control decisions based on IP address and protocol. They also 
"inspect" the session data to assure the integrity of the connection and to adapt to dynamic 
protocols. These firewalls generally provide the best speed and transparency, however, they 
may lack the granular application level access control or caching that some proxies support. 
See 

 for more information on stateful inspection.

Firewalls, of one type or another, have become an integral part of standard security solutions 
for enterprises.

The ZyXEL Device firewall is a stateful inspection firewall and is designed to protect against 
Denial of Service attacks when activated. The ZyXEL Device’s purpose is to allow a private 
Local Area Network (LAN) to be securely connected to the Internet. The ZyXEL Device can 
be used to prevent theft, destruction and modification of data, as well as log events, which may 
be important to the security of your network. The ZyXEL Device also has packet filtering 
capabilities.

The ZyXEL Device is installed between the LAN and the Internet. This allows it to act as a 
secure gateway for all data passing between the Internet and the LAN.

The ZyXEL Device has one DSL/ISDN port and one Ethernet LAN port, which physically 
separate the network into two areas.

• The DSL/ISDN port connects to the Internet.