Netopia 2200 - Manual (Page 155)

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Firewall Tutorial
admit or refuse TCP/IP connections from cer tain remote networks and specific hosts. You
will also use filters to screen par ticular types of connections. This is commonly called
fire-
walling your network.
Before creating filter sets, you should read the next few sections to learn more about how
these power ful security tools work.
What’s a filter and what’s a filter set?
A filter is a rule that lets you specify what sor t of data can flow in and out of your network.
A par ticular filter can be either an input filter—one that is used on data (packets) coming in
to your network from the Internet—or an output filter—one that is used on data (packets)
going out from your network to the Internet.
A filter set is a group of filters that work together to check incoming or outgoing data. A fil-
ter set can consist of a combination of input and output filters.
How filter sets work
A filter set acts like a team of customs inspectors. Each filter is an inspector through which
incoming and outgoing packages must pass. The inspectors work as a team, but each
inspects ever y package individually.
Each inspector has a specific task. One inspector’s task may be to examine the destina-
tion address of all outgoing packages. That inspector looks for a cer tain destination—
which could be as specific as a street address or as broad as an entire countr y—and
checks each package’s destination address to see if it matches that destination.
A filter inspects data packets like a customs inspector scrutinizing packages.
INSPECTOR
FROM:
TO:
FROM:
TO:
FROM:
TO:
APPROVED