Motorola Netopia Embedded Software, Руководство пользователя

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10-20 Administrator’s Handbook
About Filters and Filter Sets
Security should be a high priority for anyone administering a network connected to the Internet. Using packet
filters to control network communications can greatly improve your network’s security.
The Motorola Netopia® Embedded Software Version 8.7.4’s packet filters are designed to provide security for
the Internet connections made to and from your network. You can customize the gateway’s filter sets for a
variety of packet filtering applications. Typically, you use filters to selectively 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
firewalling 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 filter 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 destination 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