Mac OS X 10.5 Leopard includes a new technology called the Application Firewall. One of the basic purposes of a firewall is to control connections made to your computer from other computers on the network. In most firewall software, you must know the network ports and protocols an application uses to communicate, in order to control that application's network connections. Note: This article applies to the version of the Application Firewall included with Mac OS X 10.5.1 and later. Update to Mac OS X 10.5.1 or later if you have not yet done so. The Firewall in Leopard is an Application Firewall. This type of firewall allows you to control connections on a per-application basis, rather than a per-port basis. This makes it easier for less experienced users to gain the benefits of firewall protection and helps prevent undesirable applications from taking control of network ports that have been opened for legitimate applications. The Firewall applies to the Internet protocols most commonly used by applications, TCP and UDP. It does not affect AppleTalk. The Firewall may be set to block incoming ICMP "pings" by enabling Stealth Mode in the Advanced settings. Earlier ipfw technology is still accessible from the command line (in Terminal) and the Application Firewall does not overrule rules set with ipfw; if ipfw blocks an incoming packet, the Application Firewall will not process it. This article applies to the version of the Application Firewall included with Mac OS X 10.5.1 and later.
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