ZyXEL Communications ZyXEL ZyAIR 100 - Manual (Page 420)

ZyWALL 10~100 Series Internet Security Gateway
31-16 Filter Configuration
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
ZyWALL 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 ZyWALL 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 31-12 Protocol and Device Filter Sets
31.5 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.
31.6 Applying a Filter
This section shows you where to apply the filter(s) after you design it (them). The ZyWALL already has
filters to prevent NetBIOS traffic from triggering calls, and block incoming telnet, FTP and HTTP
connections.