Solving The "Triangle Route" Problem; Figure 54 "Triangle Route" Problem; Figure 55 Ip Alias - ZyXEL Communications P-793H User Manual

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

Figure 54 "Triangle Route" Problem

9.5.2 Solving the "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 55 IP Alias

Chapter 9 Firewall Configuration
P-793H User's Guide
135