ZyXEL Communications P-334WT Technical Information download pdf (Page 107)

● Filter Types and SUA

Conceptually, there are two categories of filter rules: device and protocol. The Generic filter rules belong to

the device category; they act on the raw data from/to LAN and WAN. The IP and IPX filter rules belong to

the protocol category; they act on the IP and IPX packets.

In order to allow users to specify the local network IP address and port number in the filter rules with SUA

connections, the TCP/IP filter function has to be executed before SUA for WAN outgoing packets and after

the SUA for WAN incoming IP packets. But at the same time, the Generic filter rules must be applied at the

point when the P-334WT is receiving and sending the packets; i.e. the ISDN interface. So, the execution

sequence has to be changed. The logic flow of the filter is shown in Figure 1 and the sequence of the logic

flow for the packet from LAN to WAN is:

1. LAN device and protocol input filter sets.

2. WAN protocol call and output filter sets.

3. If SUA is enabled, SUA converts the source IP address from 192.168.1.33 to 203.205.115.6 and port

number from 1023 to 4034.

4. WAN device output and call filter sets.

The sequence of the logic flow for the packet from WAN to LAN is:

5. WAN device input filter sets.

6. If SUA is enabled, SUA converts the destination IP address from 203.205.115.6 to 92.168.1.33 and

port number from 4034 to 1023.

7. WAN protocol input filter sets.

8. LAN device and protocol output filter sets.

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ZyXEL Communications P-334WT Technical Information Page 107