Asymmetrical Routes; Figure 141 Limited Lan To Wan Irc Traffic Example; Table 68 Limited Lan To Wan Irc Traffic Example - ZyXEL Communications ZYWALL 35 User Manual

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Chapter 11 Firewall

• has a static IP address,

• or you configure a static DHCP entry for it so the ZyWALL always assigns it the same IP

address (see

Now you configure a LAN to WAN firewall rule that allows IRC traffic from the IP address of

the CEO's computer (192.168.1.7 for example) to go to any destination address. You do not

need to specify a schedule since you want the firewall rule to always be in effect. The

following figure shows the results of your two custom rules.

Your firewall would have the following configuration.

• The first row allows the LAN computer at IP address 192.168.1.7 to access the IRC

service on the WAN.

• The second row blocks LAN access to the IRC service on the WAN.

• The third row is (still) the firewall's default policy of allowing all traffic from the LAN to

go to the WAN.

The rule for the CEO must come before the rule that blocks all LAN to WAN IRC traffic. If

the rule that blocks all LAN to WAN IRC traffic came first, the CEO's IRC traffic would

match that rule and the ZyWALL would drop it and not check any other firewall rules.

11.6 Asymmetrical Routes

If an alternate gateway on the LAN has an IP address in the same subnet as the ZyWALL's

LAN IP address, return traffic may not go through the ZyWALL. This is called an

asymmetrical or "triangle" route. This causes the ZyWALL to reset the connection, as the

connection has not been acknowledged.

You can have the ZyWALL permit the use of asymmetrical route topology on the network

(not reset the connection).

Section 6.8 on page 155

for information on static DHCP).

ZyWALL 5/35/70 Series User's Guide

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