does CentOS 4.4 have a preinstalled iptables firewall or do you have to install a firewall such as APF
NetFilter (the "firewall" code) is part of the Linux kernel. IPTables is an interface to control the NetFilter rules executed within the kernel. APF is a program that provides a user-friendly interface (at least more so than IPTables rules directly) to managing IPTables directives.
So yes, the default CentOS kernel is built with NetFilter support, and IPTables is included in the distro. The user-friendly front-ends to make it easier to manage like APF or Shorewall are not included in the default CentOS install.
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