ZyXEL Communications P-660H-Tx v2 - Manual (Page 297)

P-660H-Tx v2 User’s Guide
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Triangle Route
The Ideal Setup
When the firewall is on, your ZyXEL Device acts as a secure gateway between your LAN and
the Internet. In an ideal network topology, all incoming and outgoing network traffic passes
through the ZyXEL Device to protect your LAN against attacks.
Figure 171 Ideal Setup
The “Triangle Route” Problem
A traffic route is a path for sending or receiving data packets between two Ethernet devices.
Some companies have more than one route to one or more ISPs. If the alternate gateway is on
the LAN (and it’s IP address is in the same subnet), the “triangle route” problem may occur.
The steps below describe the “triangle route” problem.
1 A computer on the LAN initiates a connection by sending out a SYN packet to a
receiving server on the WAN.
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.