ZyXEL P-792H v2 User Guide - Page 352
Firewall Versus Filters, Applying a Filter
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Chapter 32 Filter Configuration 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 P-792H v2 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 P-792H v2 is receiving and sending the packets; in other words the interface. The interface can be an Ethernet port or any other hardware port. The following diagram illustrates this. Figure 185 Protocol and Device Filter Sets 32.5 Firewall Versus Filters Firewall configuration is discussed in Chapter 10 on page 149. Further comparisons are also made between filtering, NAT and the firewall. 32.6 Applying a Filter This section shows you where to apply the filter(s) after you design it (them). The P-792H v2 already has filters to prevent NetBIOS traffic from triggering calls, and block incoming telnet, FTP and HTTP connections. Note: If you do not activate the firewall, it is advisable to apply filters. 32.6.1 Applying LAN Filters LAN traffic filter sets may be useful to block certain packets, reduce traffic and prevent security breaches. Go to menu 3.1 (shown next) and enter the number(s) of the filter set(s) that you want to apply as appropriate. You can choose up to four filter sets (from twelve) by entering their numbers separated by commas, for 352 P-792H v2 User's Guide