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- [Instructor] It's cumbersome,

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to keep typing IP tables commands,

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into our command line interface or CLI.

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You can automate this process by creating a shell script.

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We'll start by creating a file for the shell script.

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Let's first change our working directory to Documents

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by typing cd Documents.

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Press Enter.

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Type nano, space, the name of the file, which is

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M-Y-F-W, standing for my firewall dot S-H.

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Press Enter,

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nano is one of the pre-installed Linux text editors.

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Let's start by typing iptables space dash P

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meaning the default firewall rule,

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space INPUT for all the incoming traffic.

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We'll be dropping all the incoming traffic

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which is why we type DROP next.

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Now the second rule is for the outgoing traffic.

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The net filter chain for that is output.

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We allow all the outgoing traffic

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which is why we type iptables, space, dash P, OUTPUT,

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space, ACCEPT.

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Press Enter.

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Next type iptables, space dash P space FORWARD.

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The forward chain is going to be disabled.

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Therefore we type FORWARD space DROP.

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Now save the file by pressing Control + X together.

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Type Y, press Enter to accept the current file name

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which is myfw.sh.

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Before running our shell script, we want to make sure

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our shell script is executable.

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To check this type ls space dash l.

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Press Enter.

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The permissions are read-write, read and read

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for the user of the file, group and others.

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We need to change the permissions to make a file executable.

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To do this type chmod

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standing for change mode, space, U-G-O plus sign X space

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and then the name of the file M-Y-F-W dot S-H.

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X here means executable and U-G-O plus X indicates

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adding execute permission to the user, group and others.

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Press Enter.

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Let's do ls -l again,

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to see if the file permissions have been updated.

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Press Enter.

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The color of the file name, myfw.sh is now green,

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indicating that the file is executable.

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You can also see the X is having added

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to the file permissions.

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R-W-X here, R-X for group, R-X for others.

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Finally, we're ready to run the shell script.

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Usually all you have to do is type the name

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of the shell script, but in our case,

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the commands in the shell script require root permissions,

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which is why we're typing sudo again.

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sudo space, a period, meaning the current directory,

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and then forward slash and the name of the file, myfw.sh.

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Press Enter to run the shell script.

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We lose our remote desktop connection again

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which means the shell script worked, great job!

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You just automated your Netfilter configuration process.

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We'll be using shell scripts from now on

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for all the Netfilter configuration activities.