ZyXEL Communications 1001H manual Configuring a Filter Rule, Filter Types and NAT

P100IH ISDN Router

Abbreviation

Description

SP

Source Port number

DA

Destination Address

DP

Destination Port number

zIf the filter type is GEN (generic), the following abbreviations listed in the following table will be used.

Table 9-3 Abbreviations Used If Filter Type Is GEN

Abbreviation

Description

Off

Offset

Len

Length

Refer to the next section for information on configuring the filter rules.

9.3Configuring a Filter Rule

To configure a filter rule, enter its number in Menu 21.1 - Filter Rules Summary and press [Enter] to open Menu 21.1.1 for the rule.

There are two types of filter rules: TCP/IP and Generic. Depending on the type of rule, the parameters below the type will be different. Use the space bar to select the type of rule that you wish to create in the Filter Type field and press [Enter] to open the respective menu.

9.3.1Filter Types and NAT

The network layer filters are collectively called protocol filters. 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 when the Prestige 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.

Filter Configuration 9-7