Even a continuous flow of data such as the download of a large file is broken into packets when sent, and re-assembled at its destination. This chapter and the Linux Firewall module only covers the setting up of a firewall using IPtables, not any of the older implementations like IPchains or IPfwadm.Īll IP network traffic is broken up into packets, which are chunks of data with a source, destination and protocol information. All Linux distributions that use the 2.4 kernel has IPtables support enabled, and include the commands needed to configure it. The 2.4 series of kernels include the IPtables firewall, which is more powerful and flexible than its predecessors. The Linux kernel has included several different firewall implementations over the years, such as IPfwadm and IPchains. NAT allows these internal hosts to communicate with others on the Internet, even though they do not have real public IP addresses. Typically, the hidden hosts are on an internal LAN using a private IP network (such as 192.168.0.0) and the firewall has a single Internet IP address. Typically a firewall is also a router, forwarding packets between a secure local network and the untrusted Internet - however, it is also possible for a system to protect just itself.Ī firewall system can also be configured to hide multiple hosts behind a single IP address, using a process known as NAT (Network Address Translation). Such as the source address, destination address, port and protocol. It can block packets and connections based on a variety of criteria, Introduction to firewalling with IPtablesĪ firewall is a system that protects itself and other hosts on a network from attackers on untrusted networks, such as the Internet. 7 Setting up network address translation.1 Introduction to firewalling with IPtables.
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