Filter Types And Nat; Firewall Versus Filters; Applying A Filter; Applying Lan Filters - ZyXEL Communications P-870HW-I Series User Manual

P-870HW-I1 User's Guide

30.4 Filter Types and NAT

There are two classes of filter rules, Generic Filter (Device) rules and protocol filter (TCP/
IP) rules. Generic filter rules act on the raw data from/to LAN and WAN. Protocol filter rules
act on the IP packets. 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 ZyXEL Device 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 ZyXEL Device 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 190 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 ZyXEL
Device 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

30.6.1 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, e.g., 3, 4, 6, 11. Input filter sets filter incoming
traffic to the ZyXEL Device and output filter sets filter outgoing traffic from the ZyXEL
Device. For PPPoE or PPTP encapsulation, you have the additional option of specifying
remote node call filter sets.
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Chapter 30 Filter Setup