For more usage details see iptables Command Line Tool.

The iptables command is known to yum as 'iptables'. It is also used to implement Network Address Translation (NAT). Packet filtering is most commonly used to implement firewalling functionality. Iptables is a Linux userspace command line tool that manipulates the IPv4 network packet filtering tables and rules. A registered callback function is then called for every packet that traverses the respective hook. Netfilter is a set of hooks inside the Linux kernel that allows kernel modules to register callback functions with the network stack. Netfilter, iptables tool, iptables service and firewalld As a result of this, the external firewall device should have a configuration that permits everything the most permissive of your local systems is going to need to do: each individual machine, then, can deny as much of that as it can get away with, without sacrificing its critical functionality. Each individual machine, depending on its uses, might have different packet filtering needs. It's always a good idea to have an iptables configuration in place on a given machine, regardless of outside firewalls you may have. iptables does not do string matching, because a specific string can be spread across several packets, and assembling data from different packets is too processor and memory intensive. It is possible to do some very basic filtering Application and Network access layers as well, but iptables was not designed for this, nor is it very suitable for those purposes. Iptables is specifically built to work on the headers of the Internet and the Transport layers. For more details see How State Machine Connection Tracking Works. Iptables is capable of tracking a connection's state. 3 netfilter, iptables tool, iptables service and firewalld.

Iptables chains