iptables

Question 1

What is iptables?

Answer 1

Iptables is a firewall tool built into Linux (CentOS). Iptables is the userspace module where the user can built firewall rules into predefined tables.

Iptables Iptables places rules into predefined chains (INPUT, OUTPUT and FORWARD) that are checked against any network traffic (IP packets) relevant to those chains and a decision is made about what to do with each packet based upon the outcome of those rules, i.e. accepting or dropping the packet. These actions are referred to as targets, of which the two most common predefined targets are DROP to drop a packet or ACCEPT to accept a packet.

Question 2

What are the three predefined chains?

Answer 2

Input, output and forward.

Question 3

What is an INPUT chain?

Answer 3

All packets destined for the host computer.

Question 4

What is an OUTPUT chain?

Answer 4

All packets originating from the host computer.

Question 5

What is a FORWARD chain?

Answer 5

All packets neither destined for nor originating from the host computer, but passing through (routed by) the host computer. This chain is used if you are using your computer as a router.