ZyXEL Communications P-660HW-Tx v3 User Manual page 203

9.5.3.2 Solving the "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.
A computer on the LAN initiates a connection by sending a SYN packet to a
1
receiving server on the WAN.
The ZyXEL Device reroutes the packet to Gateway A, which is in Subnet 2.
2
The reply from the WAN goes to the ZyXEL Device.
3
The ZyXEL Device then sends it to the computer on the LAN in Subnet 1.
4
Figure 70 IP Alias
LAN
P-660HW-Tx v3 User's Guide
Subnet 1
1
4
2
3
Subnet 2
WAN
ISP 1
ISP 2
A
Chapter 9 Firewalls
203