ZyXEL Communications Internet Security Gateway ZyWALL 2 Series User Manual page 544

ZyWALL 2 Series User's Guide
Diagram 2 "Triangle Route" Problem
The "Triangle Route" Solutions
This section presents you two solutions to the "triangle route" problem.
IP Aliasing
IP alias allows you to partition your network into logical sections over the same Ethernet interface. Your
ZyWALL supports up to three logical LAN interfaces with the ZyWALL being the gateway for each logical
network. By putting your LAN and Gateway B in different subnets, all returning network traffic must pass
through the ZyWALL to your LAN. The following steps describe such a scenario.
A computer on the LAN initiates a connection by sending a SYN packet to a receiving server on the WAN.
The ZyWALL reroutes the packet to Gateway B which is in Subnet 2.
The reply from WAN goes through the ZyWALL to the computer on the LAN in Subnet 1.
C-2
Triangle Route