Netopia 430 S/T, Справочное руководство

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Security 7-9
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 Netopia ISDN Router’s packet filters are designed to provide
security for the Internet connections made to and from your
network. You can customize the router’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 either be 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.