Chapter 10 Firewalls
AMG1302-T10A User’s Guide
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Once these questions have been answered, adding rules is simply a matter of entering the
information into the correct fields in the web configurator screens.
10.4.4 Triangle Route
When the firewall is on, your 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 Device
to protect your LAN against attacks.
Figure 82 Ideal Firewall Setup
10.4.4.1 The “Triangle Route” Problem
A traffic route is a path for sending or receiving data packets between two Ethernet devices. You
may have more than one connection to the Internet (through one or more ISPs). If an alternate
gateway is on the LAN (and its IP address is in the same subnet as the Device’s LAN IP address),
the “triangle route” (also called asymmetrical 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 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
Device.
As a result, the Device resets the connection, as the connection has not been acknowledged.
Figure 83 “Triangle Route” Problem
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