134. Add or Remove Firewall Rules  BEFORE YOU BEGIN 30 Configure Networking Manually 133 Enable or Disable the Firewall
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Not every network service in the world is available in the standard list of rules in the Firewall configuration pane for you to enable and disable at will. A great many more commonly used services won't work properly unless you "poke a hole" in the firewall for them. Mac OS X's firewall is designed to let you add new exception rules so that certain services can be allowed to contact your machine, even when every other unauthorized form of traffic is blocked.  NOTE You must be logged in as an Admin user , or able to authenticate as one using the lock icon in the Sharing Preferences pane, to add or remove firewall rules.
134. Add a New Firewall Rule 
| 1. | Open the Sharing Preferences
Open the System Preferences application (under the Apple menu); click the Sharing icon to open the Sharing Preferences pane. Click the Firewall tab.
| | 2. | Add a New Firewall Rule
Click the New button to the right of the list of services. This brings up a sheet where you can select from a list of commonly used network services with well-known port numbers , or define your own service that isn't in the list.
| | 3. | Select a Well-Known Service to Allow
If the service you want to allow to reach your computer is in the Port Name drop-down list, select it and click OK . The service is now immediately allowed to access your machine through the firewall.
| | 4. | Enter a Non-Standard Port Number or Range For services that aren't in the menu of popular applications, you can enter your own firewall exception rule if you know the port numbers used by the application or service you want to allow. TIP To find out what ports a certain application uses, check the application's documentation or customer support service. Another way to find a well-known port number for a common Internet application is to look in the /etc/services file; open the Terminal and type less /etc/services to browse the list of well-known services, which might contain the application you're interested in. Select Other from the Port Name drop-down list. In the Port Number, Range, or Series field, type either a single port number, a range of ports (separated by a dash), or a list of ports separated by commas. Then enter a name for the firewall rule in the Description field. Click OK when you're done. Any application whose traffic matches the ports you specified can now reach your computer from a remote source. | | 5. | Delete or Disable a Firewall Rule
To remove a firewall rule that you don't need anymore, select it and click Delete . If you prefer, you can simply disable the firewall rule, without deleting it permanently. To disable a rule, just deselect the check box next to the service's name in the list of services to remove that service's exemption.
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