Security Considerations; Triangle Route - ZyXEL Communications AMG1312-T Series User Manual

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 AMG1312-T Series 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
1
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
2
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 AMG1312-T Series 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 AMG1312-T Series to protect your LAN against attacks.
Figure 94 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 AMG1312-T Series's LAN IP
address), the "triangle route" (also called asymmetrical route) problem may occur. The steps below
describe the "triangle route" problem.
AMG1312-T Series User's Guide
LAN
1
2
WAN
Chapter 15 Firewall
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