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Advanced Setup
4.5 IP Filter/Firewall Setup
The IP Filter/Firewall function helps pretect your local network
against attack from outside. It also provides a method of restricting
users on the local network from accessing the Internet. Addition-
ally, it can filter out specific packets to trigger the router to place an
outgoing connection.
4.5.1 An Overview of the Firewall
The IP Filter/Firewall includes two types of filter: Call Filter and
Data Filter. The former is designed to block or allow IP packets
that will trigger the router to establish an outgoing connection. The
latter is designed to block or allow which kind of IP packets are
allowed to pass through the router when the WAN connection has
been established.
In concept, when an outgoing packet is to be routed to the WAN,
the IP Filter will decide if the packet should be forwarded to the
Call Filter or Data Filter. If the WAN link is down, the packet will
enter the Call Filter. If the packet is not allowed to trigger router
dialling, it will be dropped. Otherwise, it will initiate a call to estab-
lish the WAN connection.
If the WAN link of the router is up, the packet will pass through the
Data Filter. If the packet type is set to be blocked, it will be dropped.
Otherwise, it will be sent to the WAN interface. Alternatively, if an
incoming packet enters from the WAN interface, it will pass through
the Data Filter directly. If the packet type is set to be blocked, it
will be dropped. Otherwise, it will be sent to the internal LAN.
The filter architecture is shown as below.
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