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Security 13-13
Input and output filters—source and destination
There are two kinds of filters you can add to a filter set: input and output. Input filters check packets received
from the Internet, destined for your network. Output filters check packets transmitted from your network to the
Internet.
Packets in the Netopia 4752 pass through an input filter if they originate in the WAN and through an output filter if they’re being
sent out to the WAN.
The process for adding input and output filters is exactly the same. The main difference between the two
involves their reference to source and destination. From the perspective of an input filter, your local network is
the destination of the packets it checks, and the remote network is their source. From the perspective of an
output filter, your local network is the source of the packets, and the remote network is their destination.
Adding filters to a filter set
In this section you’ll learn how to add an input filter to a filter set. Adding an output filter works exactly the same
way, providing you keep the different source and destination perspectives in mind.
To add an input filter, select Add Input Filter in the Add IP Filter Set screen. The Add Filter screen appears. (To
add an output filter, select Add Output Filter.)
Type of filter Source means Destination means
Input filter The remote network The local network
Output filter The local network The remote network
The Netopia R-Series Router
input filter
output filter
LAN
WAN
packet
packet