5.13. Setting and Controlling IP sets using iptables

The essential differences between firewalld and the iptables (and ip6tables) services are:
  • The iptables service stores configuration in /etc/sysconfig/iptables and /etc/sysconfig/ip6tables, while firewalld stores it in various XML files in /usr/lib/firewalld/ and /etc/firewalld/. Note that the /etc/sysconfig/iptables file does not exist as firewalld is installed by default on Red Hat Enterprise Linux.
  • With the iptables service, every single change means flushing all the old rules and reading all the new rules from /etc/sysconfig/iptables, while with firewalld there is no recreating of all the rules. Only the differences are applied. Consequently, firewalld can change the settings during runtime without existing connections being lost.
Both use iptables tool to talk to the kernel packet filter.
To use the iptables and ip6tables services instead of firewalld, first disable firewalld by running the following command as root:
~]# systemctl disable firewalld
~]# systemctl stop firewalld
Then install the iptables-services package by entering the following command as root:
~]# yum install iptables-services
The iptables-services package contains the iptables service and the ip6tables service.
Then, to start the iptables and ip6tables services, enter the following commands as root:
~]# systemctl start iptables
~]# systemctl start ip6tables
To enable the services to start on every system start, enter the following commands:
~]# systemctl enable iptables
~]# systemctl enable ip6tables
The ipset utility is used to administer IP sets in the Linux kernel. An IP set is a framework for storing IP addresses, port numbers, IP and MAC address pairs, or IP address and port number pairs. The sets are indexed in such a way that very fast matching can be made against a set even when the sets are very large. IP sets enable simpler and more manageable configurations as well as providing performance advantages when using iptables. The iptables matches and targets referring to sets create references which protect the given sets in the kernel. A set cannot be destroyed while there is a single reference pointing to it.
The use of ipset enables iptables commands, such as those below, to be replaced by a set:
~]# iptables -A INPUT -s -j DROP
~]# iptables -A INPUT -s -j DROP
~]# iptables -A INPUT -s -j DROP
The set is created as follows:
~]# ipset create my-block-set hash:net
~]# ipset add my-block-set
~]# ipset add my-block-set
~]# ipset add my-block-set
The set is then referenced in an iptables command as follows:
~]# iptables -A INPUT -m set --set my-block-set src -j DROP
If the set is used more than once a saving in configuration time is made. If the set contains many entries a saving in processing time is made.