Terminal Commands Archives

Inspecting DNS traffic via tcpdump

Posted on April 3, 2020May 20, 2020 by Daniel Cid

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):

Blocking HTTP requests via Iptables for a specific domain

Posted on March 14, 2020May 20, 2020 by Daniel Cid

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.

Binding multiple IPv6 addresses automatically

Posted on March 7, 2020May 20, 2020 by Daniel Cid

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:

How To List UFW Rules When The Application is Inactive or Disabled

Posted on February 8, 2020May 20, 2020 by Tony

When working on your server you might need to disable the Uncomplicated Firewall (UFW). When doing so you’ll notice it doesn’t display your rules when the application is inactive.

Working with UFW – Uncomplicated Firewall – on Ubuntu

Posted on January 31, 2020May 20, 2020 by Tony

This is not a comprehensive guide to the UFW application.

It is a basic orientation for the UFW application. This should provide insights you’re probably not aware of, but many might assume you already know.