1 Packet flow in the Linux kernel, source Wikipedia QOS - using the tc filter command design for QOS filteringįiltration on OSI layer 7 using a user space applicationīefore we begin: just a quick reminder about packet flow in the Linux kernel:įig. BGP Flow Spec (how to deploy iptables’ rules using BGP protocol).IP routing - transferring packets according to the routing table Ip rule - a tool designed to build advanced routing policies Nftables - successor of iptables+ebtables Iptables - responsible for filtering packets handled by TCP/IP stackĮbtables - the same as above, but mostly focused on layer 2 (the comparison between ISO/OSI and TCP/IP models is presented in our infographic) These methods are not restricted to just firewall rules and can be divided into six main categories: In this blog post we want to share them with you. iptables Command Examplesġ.Have you ever wondered how to drop a packet in Linux OS? Well, there are a few methods to do it. To save the current iptables in memory, you would use something like iptables-save > /etc/les. If you want to save the rules so they survive a reboot, you either need to edit the iptables configuration file directly or save the iptables currently in memory. It is important to note that any rules applied with the iptables command are not persistent through a reboot. The command can be handy if we need to troubleshoot a firewall, and it can be reversed with iptables -P INPUT DROP. We can change the default policy with the command iptables -P INPUT ACCEPT, which will allow any traffic even if it is not defined in the INPUT table. The INPUT table also has a default policy of DROP that defines what to do with the traffic if no rule matches. In this example, the INPUT table has several rules configured. ACCEPT tcp - anywhere anywhere tcp dpt:sshĪCCEPT tcp - anywhere anywhere tcp dpt:smtpĪCCEPT icmp - anywhere anywhere icmp echo-request

Iptables command in linux