Dan Kaminsky discovered that properties inherent to the DNS protocol lead to practical DNS cache poisoning attacks. Among other things, successful attacks can lead to misdirected web traffic and email rerouting.
By default Apache webserver listen on port 80 (http) and port 443 (https i.e. secure http). Apache webserver uses the TCP protocol to transfer information/data between server and browser. The default Iptables configuration does not allow inbound access to the HTTP (80) and HTTPS (443) ports used by the web server. This post explains how to allow inbound and outbound access to web services under Linux.