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Iptables is a firewall software used in Linux that filters packets through tables of rules to determine whether they are allowed and how they are handled. Rules classify packets based on identifying information, and the chains determine how the system distributes them. Iptables is fully configurable and customizable, and can also be used for IP masquerading, transparent proxies, and analyzing logs. It is usually installed by default on most Linux operating system distributions.
Iptables is a firewall software used in Linux software distributions that works by filtering packets through a system of tables containing a chain of packet filtering rules. The chains and sets of rules contained in the firewall determine whether a packet is allowed and, if so, how it is handled. The tables themselves are kept in memory and the iptables software provides configuration of the chains within the tables.
Every data packet sent over a network has identifying information that is read by the receiving system. The Iptables software takes this information and determines what to do with it by moving it through a series of chained rules. Rules work to classify the packet based on its identifying information, such as an Internet Protocol (IP) address. After being identified, the packet moves from one chain to another, depending on the set of rules configured. The chains determine how the system distributes the package.
Rules are criteria for how a packet moves through iptables decision chains. The packet will move from one rule to another, as long as it meets the requirements for each chain. Each packet will be accepted, forwarded, discarded, queued, reset or returned.
Accepting moves the package to the next chain, and deleting removes the package completely. If the package is queued, it is moved and routed to a separate queue manager within userspace. When a packet is returned, it reverts to the last accepted chain.
Iptables is a user-space application, which means that it operates within a segregated space within the Linux kernel functionality. The policies used to identify and distribute packets from the firewall are fully configurable and customizable using a variety of command options. This includes setting allowance for established sessions, blocking types of traffic and access, and allowing only specific traffic on certain ports. The software can also be configured to log all incoming traffic or to log specific types of traffic only.
The Iptables software is maintained by the Nefilter project and began in 1998. In addition to being used as firewall and packet manipulation software, Iptables can also be used for IP masquerading, implementing transparent proxies, and analyzing logs . This allows the firewall to detect and prevent potentially harmful activity, further protecting your system. The software is also ready for configuration with third-party extensions, as it contains different levels of application programming interfaces. Iptables is usually installed by default on most Linux operating system distributions.
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