Netopia 2200 manual What’s a filter and what’s a filter set?, How filter sets work, 155

Firewall Tutorial

admit or refuse TCP/IP connections from certain remote networks and specific hosts. You will also use filters to screen particular 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 powerful security tools work.

What’s a filter and what’s a filter set?

A filter is a rule that lets you specify what sort of data can flow in and out of your network. A particular 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 every 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 certain destination— which could be as specific as a street address or as broad as an entire country—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.

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