ZyXEL Communications Prestige 2602HW Series, User Manual

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Prestige 2602HW Series User’s Guide
160 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.
13.7 Packet Filtering Vs Firewall
Below are some comparisons between the Prestige’s filtering and firewall functions.
13.7.1 Packet Filtering:
• 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.
13.7.1.1 When To Use Filtering
• 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.
13.7.2 Firewall
• 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.