ZyXEL Communications ZyWALL 5 User Manual page 138

ZyWALL 5 Internet Security Appliance
3. 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 cannot distinguish traffic originating from an
inside host or an outside host by IP address.
4. To block/allow IP trace route.
9.7.2 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.
The firewall provides e-mail service to notify you of routine reports and when alerts occur.
When To Use The Firewall
1. To prevent DoS attacks and prevent hackers cracking your network.
2. A range of source and destination IP addresses as well as port numbers can be specified within one
firewall rule making the firewall a better choice when complex rules are required.
3. To selectively block/allow inbound or outbound traffic between inside host/networks and outside
host/networks. Remember that filters cannot distinguish traffic originating from an inside host or
an outside host by IP address.
4. The firewall performs better than filtering if you need to check many rules.
5. Use the firewall if you need routine e-mail reports about your system or need to be alerted when
attacks occur.
6. The firewall can block specific URL traffic that might occur in the future. The URL can be saved
in an Access Control List (ACL) database.
9-10 Firewalls