Security 7-9About filters and filter setsSecurity should be a high priority for anyone administering a networkconnected to the Internet. Using packet filters to control networkcommunications can greatly improve your network’s security.The Netopia ISDN Router’s packet filters are designed to providesecurity for the Internet connections made to and from yournetwork. You can customize the router’s filter sets for a variety ofpacket filtering applications. Typically, you use filters to selectivelyadmit or refuse TCP/IP connections from certain remote networksand specific hosts. You will also use filters to screen particulartypes of connections. This is commonly called firewalling yournetwork.Before creating filter sets, you should read the next few sections tolearn 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 inand out of your network. A particular filter can either be an inputfilter—one that is used on data (packets) coming in to your networkfrom 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 incomingor outgoing data. A filter set can consist of a combination of inputand output filters.How filter sets workA filter set acts like a team of customs inspectors. Each filter is aninspector through which incoming and outgoing packages mustpass. The inspectors work as a team, but each inspects everypackage individually.
