ZyXEL Communications P-324 User's Guide download pdf (Page 214)

P-2602HWNLI User’s Guide

214 Chapter 14 Firewall Configuration

14.4.1 LAN to WAN Rules

The default rule for LAN to WAN traffic is that all users on the LAN are allowed non-

restricted access to the WAN. When you configure a LAN to WAN rule, you in essence want

to limit some or all users from accessing certain services on the WAN. WAN to LAN Rules

The default rule for WAN to LAN traffic blocks all incoming connections (WAN to LAN). If

you wish to allow certain WAN users to have access to your LAN, you will need to create

custom rules to allow it.

14.4.2 Alerts

Alerts are reports on events, such as attacks, that you may want to know about right away. You

can choose to generate an alert when a rule is matched in the Edit Rule screen (see Figure 114

on page 220).

When an event generates an alert, a message can be immediately sent to an e-

mail account that you specify in the Log Settings screen. Refer to the chapter on logs for

details.

14.5 Triangle Route

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 109 Ideal Firewall Setup

14.5.1 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 ZyXEL

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 ZyXEL Device reroutes the SYN packet through Gateway A on the LAN to the

WA N.

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ZyXEL Communications P-324 User's Guide Page 214