User's Manual

134 Chapter 11 Filter configuration
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are replaced on a connection-by-connection basis, which makes it impossible to
know the exact address and port on the wire. Therefore, the BCM50a Integrated
Router 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 BCM50a Integrated Router is
receiving and sending the packets; for example. the interface. The interface can be
an Ethernet port or any other hardware port, as illustrated in Figure 63.
Figure 63 Protocol and Device Filter Sets
Firewall Versus Filters
Firewall configuration is discussed in Chapter 10, “Introducing the firewall,” on
page 115 chapters of this manual. Further comparisons are also made between
filtering, NAT and the firewall.
Applying a Filter
This section shows you where to apply the filters after you design them. The
BCM50a Integrated Router already has filters to prevent NetBIOS traffic from
triggering calls, and block incoming Telnet, FTP and HTTP connections.
Note: Nortel recommends that you apply filters if you do not activate
the firewall.