ZyXEL Communications Prestige 792H, User Manual

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Prestige 792H User’s Guide
Firewall 8-13
8.7.1 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.
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.
8.7.2 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
To prevent DoS attacks and prevent hackers cracking your network.
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.