ZyXEL p-2802h-i1 Guia Do Utilizador

 Chapter 11 Firewalls

P-2802H(W)(L)-I Series User’s Guide

2 The ZyXEL Device reroutes the SYN packet through Gateway A on the LAN to the 

WAN. 

3 The reply from the WAN goes directly to the computer on the LAN without going 

through the ZyXEL Device. 

As a result, the ZyXEL Device resets the connection, as the connection has not been 
acknowledged.

Figure 86   “Triangle Route” Problem

If you have the ZyXEL Device allow triangle route sessions, traffic from the WAN can go 
directly to a LAN computer without passing through the ZyXEL Device and its firewall 
protection. 
Another solution 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. 
It’s like having multiple LAN networks that actually use the same physical cables and ports. 
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.