up a simple firewall in Fedora LinuxWhen you (Net web server)
up a simple firewall in Fedora LinuxWhen you installed Fedora, you ran a program calledsystem-config-security. You might not have evennoticed it it s part of the installation script, andgoes by with just a quick question or two. At installa- tion time, it created a firewall and firewall rules foryou. You may have chosen not to install a firewall atthat time; if that s the case, you have no firewallrules in place. If you chose not to install a firewall when youinstalled Fedora, you can change your mind later. The same configuration tool that runs during theinstall procedure will create (or remove) simple firewall rules. To run Fedora s firewall builder, followthese steps: 1.Open the Main Menu and chooseSystemSettings.Security Level. You re prompted for the rootpassword. 2.Enter the rootpassword and click OK. If you have a terminal window open and super- user privileges, you can start the configurationtool by entering system-config- securitylevelat the command line. The Security Level Configuration dialog opens. This dialog is similar to the firewall informationwindow you saw at installation time. 3.From the Security Level drop-down list, selectEnable Firewall. If you disablethe firewall, any custom rulesyou ve created are lost. 4.To create the most robust firewall possible, enable the firewall with no trusted services ortrusted devices. That is, deselect all the check boxes, as shown inFigure 34-2. The best way to build a robust firewall is todisallow all traffic, and then relax the restric- tions to allow data to flow. It s easier to recog- nize your friends one at a time. Figure 34-2: A very secure firewall. If you have multiple network cards listed inthe Trusted Devices frame, you can trustdevices that connect to your own network, butdon t trust the devices that connect to the out- side world. That way, the devices within yournetwork can access the machine via SSH orTelnet, but the outside world can t get in. 5.Click the OK button to continue. A pop-up opens, warning you that if you con- tinue, you ll change the existing firewall configuration. 6.Click Yes to continue.
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