ZyXEL Communications P-334W - Manual (Page 372)

Prestige 334W User’s Guide
30-16 Filter Configuration
Generic and TCP/IP filter rules are discussed in more detail in the next section. When NAT (Network
Address Translation) is enabled, the inside IP address and port number are replaced on a connection-by-
connection basis, which makes it impossible to know the exact address and port on the wire. Therefore, the
Prestige applies the protocol filters to the “native” IP address and port number before NAT for outgoing
packets and after NAT for incoming packets. On the other hand, the generic, or device filters are applied to
the raw packets that appear on the wire. They are applied at the point when the Prestige is receiving and
sending the packets; i.e. the interface. The interface can be an Ethernet port or any other hardware port. The
following diagram illustrates this.
Figure 30-12 Protocol and Device Filter Sets
30.5 Firewall Versus Filters
Firewall configuration is discussed in the firewall chapters of this manual. Further comparisons are also made
between filtering, NAT and the firewall.
30.6 Applying a Filter
This section shows you where to apply the filter(s) after you design it (them). The Prestige already has filters
to prevent NetBIOS traffic from triggering calls, and block incoming telnet, FTP and HTTP connections.
If you do not activate the firewall, it is advisable to apply filters.