bookmark_borderTips and Tricks: Blocking DNS requests via Iptables

If there is a tool we love, it is called iptables. The default firewall tool chain on Linux has a lot of options to filter pretty much any traffic you wish.

In this Tips and Tricks, we will show you how to block DNS requests (domain names) via iptables. Enjoy!

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bookmark_borderBriefly unavailable for scheduled maintenance. Check back in a minute.

Every now and then, depending on what you’re doing, you might encounter this problem with your WordPress site. I often see it after running an update:

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bookmark_borderCreate MySql Database Backup in Linux Using MariaDB

If you need to do a MySQL database backup in linux, this is the basic command structure you want to use:

# mysqldump -u [username] -p [database name] > [filename]-$(date +%F).sql

This will prompt the password when you hit enter.

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bookmark_borderInspecting DNS traffic via tcpdump

If you ever wondered what is going on at the DNS level on your computer (or network), tcpdump can be a useful tool for you.

TCPdump basics

Tcpdump is a tool that allows you to inspect any packet (TCP, UDP, etc) and its content as they pass through an interface through the libpcap module. The syntax is very simple, but the basics of the command require the network interface name, the protocol and the restrictions of what you are trying to inspect (more on that later):

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bookmark_borderActive Domain Error in GravityForms MailGun plugin

For whatever reason I have was having the hardest time getting the MailGun plugin for GravityForms to use my From Email domain in WordPress.

Every time I tried to update the settings, I’d get the following error:

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bookmark_borderBlocking HTTP requests via Iptables for a specific domain

In a previous article, we showed how to block specific domains at the DNS level using iptables. Today, we will expand into that and show how to also block HTTP requests for a specific domain (or URL) in there.

Iptables String Matching

Iptables string matching is very powerful and easier to use than the hex-string module we used before. When you specify -m string –string, it will activate the string module and inspect at the packet content for the keyword you are looking for.

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bookmark_borderBinding multiple IPv6 addresses automatically

Most servers get a IPv6 range (/64) by default. That means that you have millions of IP addresses to use for whatever you feel like. However, assigning them manually to your interfaces can be a bit painful.

Assigning all /64 IPv6 addresses with 1 command

However, there is a trick with the ip route command that allows you to link your /64 to the local interface and cover all of them automatically:

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bookmark_borderMySQL – ERROR 1819 (HY000): Your password does not satisfy the current policy requirements

If you run into this error it’s a strong indicator that the Password Validation Plugin is installed.

The quick and dirty way to fix this is to uninstall the plugin. You will need to be the root user in the database.

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bookmark_borderRemoving Index.php From the URL Slug in WordPress

This post assumes you’re having a hard time removing the index.php file name from the URL slug of your WordPress site.

Looks like something like this:

defragged.org/index.php/%postname%

This means one of two things:

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bookmark_borderLets Encrypt: Unable to install the certificate

You’ve heard it’s important to install Let’s Encrypt (LE). You spin up your Ubuntu 18.04 machine and try to use https://certbot.eff.org/.

You run the command:

certbot –apache -d domain.com

You are greeted with:

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