Unified Security Gateway User's Guide

Chapter 19 Firewall
ZyWALL USG 1000 User’s Guide
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You can have the ZyWALL permit the use of asymmetrical route topology on the network
(not reset the connection).
Allowing asymmetrical routes may let traffic from the WAN go directly to the LAN without
passing through the ZyWALL. A better solution is to use virtual interfaces to put the
ZyWALL and the backup gateway on separate subnets.
19.5.1 Virtual Interfaces and Asymmetrical Routes
You can use virtual interfaces instead of allowing asymmetrical routes. Virtual interfaces
allow you to partition your network into logical sections over the same interface. See the
chapter about interfaces for more information.
By putting your LAN and Gateway A in different subnets, all returning network traffic must
pass through the ZyWALL to your LAN. The following steps describe such a scenario.
1 A computer on the LAN initiates a connection by sending a SYN packet to a receiving
server on the WAN.
2 The ZyWALL reroutes the packet to Gateway A, which is in Subnet 2.
3 The reply from the WAN goes to the ZyWALL.
4 The ZyWALL then sends it to the computer on the LAN in Subnet 1.
Figure 185 Triangle Route: Using Virtual Interfaces
19.6 Configuring the Firewall
Click Firewall to open the Firewall screen. This screen varies depending on the firewall rule
type and the way you choose to display the firewall rules.
" The ordering of your rules is very important as rules are applied in sequence.
Specify from which zone packets come and to which zone packets travel to display only the
rules specific to the selected direction.