Security Considerations; Triangle Route - ZyXEL Communications AMG1302-T series User Manual

Chapter 15 Firewall
11 Protect against IP spoofing by making sure the firewall is active.
12 Keep the firewall in a secured (locked) room.

15.6.3 Security Considerations

Note: Incorrectly configuring the firewall may block valid access or introduce security
risks to the AMG1302/AMG1202-TSeries and your protected network. Use caution
when creating or deleting firewall rules and test your rules after you configure
them.
Consider these security ramifications before creating a rule:
Does this rule stop LAN users from accessing critical resources on the Internet? For example, if IRC
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is blocked, are there users that require this service?
Is it possible to modify the rule to be more specific? For example, if IRC is blocked for all users, will
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a rule that blocks just certain users be more effective?
Does a rule that allows Internet users access to resources on the LAN create a security
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vulnerability? For example, if FTP ports (TCP 20, 21) are allowed from the Internet to the LAN,
Internet users may be able to connect to computers with running FTP servers.
Does this rule conflict with any existing rules?
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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.

15.6.4 Triangle Route

When the firewall is on, your AMG1302/AMG1202-TSeries 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 AMG1302/AMG1202-TSeries to protect your LAN against attacks.
Figure 90 Ideal Firewall Setup
15.6.4.1 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 AMG1302/AMG1202-
TSeries's LAN IP address), the "triangle route" (also called asymmetrical route) problem may occur.
The steps below describe the "triangle route" problem.
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LAN
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2
WAN
AMG1302/AMG1202-TSeries User's Guide