ZyXEL p-662h-61 Guia Do Utilizador

Prestige 662HW Series User’s Guide

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Chapter 13 Firewalls

• Upgrade your software regularly. Many older versions of software, especially web 

browsers, have well known security deficiencies. When you upgrade to the latest 
versions, you get the latest patches and fixes.

• If you use “chat rooms” or IRC sessions, be careful with any information you reveal to 

strangers.

• If your system starts exhibiting odd behavior, contact your ISP. Some hackers will set off 

hacks that cause your system to slowly become unstable or unusable. 

• Always shred confidential information, particularly about your computer, before 

throwing it away. Some hackers dig through the trash of companies or individuals for 
information that might help them in an attack.

Below are some comparisons between the Prestige’s filtering and firewall functions.

• The router filters packets as they pass through the router’s interface according to the filter 

rules you designed.

• Packet filtering is a powerful tool, yet can be complex to configure and maintain, 

especially if you need a chain of rules to filter a service.

• Packet filtering only checks the header portion of an IP packet.

• To block/allow LAN packets by their MAC addresses.

• To block/allow special IP packets which are neither TCP nor UDP, nor ICMP packets.

• To block/allow both inbound (WAN to LAN) and outbound (LAN to WAN) traffic 

between the specific inside host/network "A" and outside host/network "B". If the filter 
blocks the traffic from A to B, it also blocks the traffic from B to A. Filters can not 
distinguish traffic originating from an inside host or an outside host by IP address.

• To block/allow IP trace route.

• The firewall inspects packet contents as well as their source and destination addresses. 

Firewalls of this type employ an inspection module, applicable to all protocols, that 
understands data in the packet is intended for other layers, from the network layer (IP 
headers) up to the application layer.

• The firewall performs stateful inspection. It takes into account the state of connections it 

handles so that, for example, a legitimate incoming packet can be matched with the 
outbound request for that packet and allowed in. Conversely, an incoming packet 
masquerading as a response to a nonexistent outbound request can be blocked.

• The firewall uses session filtering, i.e., smart rules, that enhance the filtering process and 

control the network session rather than control individual packets in a session.