Iptables: deffinition & operation

Iptables

     Is a free software of Linux user space through which the system administrator can configure the chains and rules in the firewall.
   

     Iptables is used for IPv4, Ip6tables for IPv6, ARP for Arptables.
     Such changes must be reserved for the system administrator. Therefore, its use requires the use of the root account. Using the program is denied to other users. On most Linux distributions, Iptables is launched by the /usr/sbin/ or /etc/sysconfig

Operation

     Xtables allows the system administrator to create tables , which contain "chains" , themselves composed of a set of packet processing rules.
     Each network packet, incoming or outgoing , so through at least one channel. The system administrator can create as many other channels they like. These channels do not have a policy that if a packet arrives at the end of the string , it is returned to the chain that called . A string can even be empty ( have no rule). The five preset channels are as follows:

• PREROUTING: The packets will enter this string before a routing decision is made.
• INPUT: The package will be delivered on site
• FORWARD: All the packets that were sent and not delivered locally run through the chain.
• OUTPUT: The packets sent from the machine itself will go to that channel.
• POSTROUTING: The routing decision was made . The packages are in this chain, just before they are sent to the hardware.

                                                                                                                       To be continued ...

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I am a cloud engineering student, I am interested in system and network admnistration. I am looking for an intership in order to get my engineer diploma, the internship I am looking for would preferably be of 6 up to 10 months long counting from december 2015.