ZyXEL 2WG Guida Utente

Chapter 12 Firewall Screens

ZyWALL 2WG User’s Guide

Allow 

Asymmetrical 

Route

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.
Select this check box to have the ZyWALL permit the use of asymmetrical route 

topology on the network (not reset the connection). 

Note: 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 IP alias to put the ZyWALL and the 
backup gateway on separate subnets. See 

 for an example. 

From, To

The firewall rules are grouped by the direction of packet travel. This displays the 

number of rules for each packet direction. Click the edit icon to go to a summary 

screen of the rules for that packet direction.
Here are some example descriptions of the directions of travel.
From LAN To LAN means packets traveling from a computer on one LAN subnet to 

a computer on another LAN subnet on the LAN interface of the ZyWALL or the 

ZyWALL itself. The ZyWALL does not apply the firewall to packets traveling from a 

LAN computer to another LAN computer on the same subnet.
From VPN means traffic that came into the ZyWALL through a VPN tunnel and is 

going to the selected “to” interface. For example, From VPN To LAN specifies the 

VPN traffic that is going to the LAN. The ZyWALL applies the firewall to the traffic 

after decrypting it. 
To VPN is traffic that comes in through the selected “from” interface and goes out 

through any VPN tunnel. For example, From LAN To VPN specifies the traffic that 

is coming from the LAN and going out through a VPN tunnel. The ZyWALL applies 

the firewall to the traffic before encrypting it. 
From VPN To VPN means traffic that comes in through a VPN tunnel and goes out 

through (another) VPN tunnel or terminates at the ZyWALL. This is the case when 

the ZyWALL is the hub in a hub-and-spoke VPN. This is also the case if you allow 

someone to use a service (like Telnet or HTTP) through a VPN tunnel to manage the 

ZyWALL. The ZyWALL applies the firewall to the traffic after decrypting it. 

Note: The VPN connection directions apply to the traffic going to or 

from the ZyWALL’s VPN tunnels. They do not apply to other 
VPN traffic for which the ZyWALL is not one of the gateways 
(VPN pass-through traffic). 

Use the drop-down list box to set the firewall’s default actions based on the direction 

of travel of packets. 
Select Drop to silently discard the packets without sending a TCP reset packet or an 

ICMP destination-unreachable message to the sender.
Select Reject to deny the packets and send a TCP reset packet (for a TCP packet) 

or an ICMP destination-unreachable message (for a UDP packet) to the sender.
Select Permit to allow the passage of the packets. 
The firewall rules for the WAN port with a higher route priority also apply to the dial 

backup connection.

Log

Select the check box next to a direction of packet travel to create a log when the 

above action is taken for packets that are traveling in that direction and do not match 

any of your customized rules.

Apply

Click Apply to save your changes back to the ZyWALL.

Reset

Click Reset to begin configuring this screen afresh.

Table 68   SECURITY > FIREWALL > Default Rule (Router Mode) (continued)