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Prestige 660RU-Tx Series User’s Guide

187 Chapter 22 Filter Configuration

22.5 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 IP packets.

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 where the Prestige is receiving

and sending the packets; for instance, the interface. The interface can be an Ethernet, or any

other hardware port. The following figure illustrates this.

Figure 124 Protocol and Device Filter Sets

22.6 Example Filter

Let’s look at an example to block outside users from telnetting into the Prestige.

Action Not

Matched

Select the action for a packet not matching the rule. Choices are Check Next Rule,

Forward or Drop.

When you have completed this menu, press [ENTER] at the prompt “Press ENTER to Confirm

or ESC to Cancel:

” to save your configuration, or press [ESC] at any time to cancel.

Table 56 Menu 21.1.5.1 Generic Filter Rule (continued)

FIELD DESCRIPTION

1 2 ... 183 184 185 186 187 188 189 190 191 192 193 ... 285 286

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ZyXEL ADSL2+ User Manual Page 188