Table 50 Security > Firewall > Default Rule (Router Mode) - ZyXEL Communications ZYWALL 2 PLUS User Manual

Chapter 11 Firewall
The following table describes the labels in this screen.
Table 50 SECURITY > FIREWALL > Default Rule (Router Mode)
LABEL
Enable Firewall
Allow
Asymmetrical
Route
From, To
Log
192
DESCRIPTION
Select this check box to activate the firewall. The ZyWALL performs access control
and protects against Denial of Service (DoS) attacks when the firewall is activated.
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 Section 11.6.1 on page 190
Set the firewall's default actions based on the direction of travel of packets. 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).
Here are the default actions from which you can select.
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.
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.
for an example.
ZyWALL 2 Plus User's Guide