ZyXEL Communications P-660H-61 User Manual page 179

The ZyXEL Device reroutes the SYN packet through Gateway A on the LAN to the WAN.
2
The reply from the WAN goes directly to the computer on the LAN without going through the ZyXEL
3
Device.
As a result, the ZyXEL Device resets the connection, as the connection has not been acknowledged.
Figure 82 "Triangle Route" Problem
10.7.4.2 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 receiving server on the
1
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
ADSL Router Series User's Guide
LAN
1
2
3
WAN
ISP 1
ISP 2
A
Chapter 10 Firewall
179