In this video we look at a few more examples of rules, in this case, by ip address. These rules are just about identical, whether you're configuring them for ipv4, or ipv6 addresses. All you need to do is use ip4tables for version 4 and ip6tables for version 6. The first sample command here takes the input from the 192 dot 168 dot 0 dot 10 ip address and accepts it. The second command takes input from all systems on the 10 dot 20 dot 30 dot 0 network, and evaluates it for icmp packets usually associated with the ping command, and drops them. In other words, if anyone from that network tries to ping your Firewall, those pings don't get through. The next command here results in a destination unreachable message sent to anyone on the 10 dot 30 dot 50 dot 0 network. Note how I organize ip addresses in these iptables commands. In some of them I use the full subnet mask, in others I use CIDR notation. They work equally well. I can also use the bang character, also known as the exclamation point, to reverse the effect of a command. For example, if I add an exclamation point to the previous command, it sends the destination unreachable message to everyone else, but people on the 10 dot 30 dot 50 dot 0 network. Of course, networking goes both ways, so as you can specify source addresses, you can also specify destination addresses. This command is just one example that allows network traffic to a destination address of 192 dot 168 dot 0 dot 1. If you're creating a basic Firewall using the security level configuration tool, you may just want to add a bit to it, so you need to know how to manage the chain. In that case, an iptables dash A command is not what you want, as it adds the rule to the end of a chain, and the last rule in a Firewall, at least that created with the security level configuration tool, rejects packets, so if you add a rule after that, that's of no use. So you may want to insert the rule into an established iptables chain, and that requires the dash I switch. If you use the dash I and specify the chain, in this case the name of the chain is RH dash firewall dash 1 dash input, you'll also want to specify the rule number, otherwise it goes to the top of the chain. So, to add the rule to the chain, let's add it after the rule associated with the ping command. This is the first rule. This is the second rule of the RH dash firewall dash 1 dash input chain. So, let's make it the third rule. Specifically, let's say iptables insert into the RH Firewall dash 1 dash input rule as rule number 3, anything from the source address of the 192 dot 168 dot 0 dot 0 class c network and a destination address of the same network. Remember, network messages go both ways, and we want all such messages to be accepted. That's the right command. And let's check out the result. To list current iptables rules run the iptables dash L command. And there it is, as rule number 1, 2, 3. Hurray. All messages to and from the 192 dot 168 dot 0 dot 0 network are now accepted by the Firewall. But this change doesn't survive a reboot, so you may need to make changes to the configuration file. You could add the command to a boot file such as etc slash RC dot local, or a simpler way to save the new settings is with the etc slash init dot d slash iptables save command. And there's the rule we added.
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