ZyXEL UAG715 User Guide - Page 242
The Firewall Screen
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Chapter 21 Firewall 21.2 The Firewall Screen Asymmetrical Routes If an alternate gateway on the LAN has an IP address in the same subnet as the UAG's LAN IP address, return traffic may not go through the UAG. This is called an asymmetrical or "triangle" route. This causes the UAG to reset the connection, as the connection has not been acknowledged. You can have the UAG permit the use of asymmetrical route topology on the network (not reset the connection). However, allowing asymmetrical routes may let traffic from the WAN go directly to the LAN without passing through the UAG. A better solution is to use virtual interfaces to put the UAG and the backup gateway on separate subnets. 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 LAN 1 and the alternate gateway (A in the figure) in different subnets, all returning network traffic must pass through the UAG to the LAN. The following steps and figure describe such a scenario. 1 A computer on the LAN1 initiates a connection by sending a SYN packet to a receiving server on the WAN. 2 The UAG reroutes the packet to gateway A, which is in Subnet 2. 3 The reply from the WAN goes to the UAG. 4 The UAG then sends it to the computer on the LAN1 in Subnet 1. Figure 161 Using Virtual Interfaces to Avoid Asymmetrical Routes 21.2.1 Configuring the Firewall Screen Click Configuration > Firewall to open the Firewall screen. Use this screen to enable or disable the firewall and asymmetrical routes, set a maximum number of sessions per host, and display the configured firewall rules. Specify from which zone packets come and to which zone packets travel to display only the rules specific to the selected direction. Note the following. 242 UAG715 User's Guide