Chapter 38 Filter Configuration

After you’ve created the filter set, you must apply it.

1Enter 11 from the main menu to go to menu 11.

2Enter 1 or 2 to open Menu 11.x - Remote Node Profile.

3Go to the Edit Filter Sets field, press [SPACE BAR] to select Yes and press [ENTER].

4This brings you to menu 11.1.4. Apply a filter set (our example filter set 3) as shown in Figure 381 on page 555.

5Press [ENTER] to confirm after you enter the set numbers and to leave menu 11.1.4.

38.4Filter 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 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 378 Protocol and Device Filter Sets

38.5 Firewall Versus Filters

Below are some comparisons between the ZyWALL’s filtering and firewall functions.

38.5.1Packet Filtering:

•The router filters packets as they pass through the router’s interface according to the filter rules you designed.

•Packet filtering is a powerful tool, yet can be complex to configure and maintain, especially if you need a chain of rules to filter a service.

•Packet filtering only checks the header portion of an IP packet.

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ZyWALL 2 Plus User’s Guide