ZyXEL Communications P-660HN-F1A, Руководство пользователя

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Chapter 12 Packet Filter
P-660HN-F1A User’s Guide
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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
1
To block/allow LAN packets by their MAC addresses.
2
To block/allow special IP packets which are neither TCP nor UDP, nor ICMP
packets.
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.
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 non-existent 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.