ZyXEL Communications P-793H User Manual

 Chapter 9 Firewall Configuration

P-793H User’s Guide

Figure 58   “Triangle Route” Problem

You can have the ZyXEL Device allow triangle route sessions. However this can allow traffic 
from the WAN to go directly to a LAN computer without passing through the ZyXEL Device 
and its firewall protection. 
Another way to solve the triangle route problem is to use IP alias. IP alias allows you to 
partition your network into logical sections over the same Ethernet interface. Your ZyXEL 
Device supports up to three logical LAN interfaces with the ZyXEL Device being the gateway 
for each logical network. By putting your LAN and Gateway A in different subnets, all 
returning network traffic must pass through the ZyXEL Device to your LAN. The following 
steps describe such a scenario.

1 A computer on the LAN initiates a connection by sending a SYN packet to a receiving 

server on the WAN. 

2 The ZyXEL Device reroutes the packet to Gateway A, which is in Subnet 2. 
3 The reply from the WAN goes to the ZyXEL Device. 
4 The ZyXEL Device then sends it to the computer on the LAN in Subnet 1. 

Figure 59   IP Alias

Click Security > Firewall to display the following screen. Activate the firewall by selecting 
the Active Firewall check box as seen in the following screen.
Refer to 

 for more information.