ZyXEL Communications Prestige 653HWI series, Руководство пользователя

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Prestige 653HWI Series User’s Guide
Firewalls 11-13
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.
11.7.2 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.