<p>There are shortcomings in using iptables to perform this interception. Since netfilter is a highly versatile tool for filtering packets, several routing rules and data filtering processes are applied before reaching the destination socket. For example, from the network layer to the transport layer, netfilter will be used for processing for several times with the rules predefined, like <code>pre_routing</code>, <code>post_routing</code> and etc. When the packet becomes a TCP packet or UDP packet, and is f