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Advanced Setup
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 estab-
lished.
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 establish the WAN con-
nection.
If the router's WAN link 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.
5-15
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