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@@ -4,16 +4,28 @@ robinkrens.nl - Linux Resources
 This page lists some useful resources for a more in depth understanding on specific subjects. Assumed is that you have a basic understanding of Linux and Networking. If not, you might to start with one of the followings books
 
 	* http://linux-training.be - PDFs about the fundamentals, gives an overview of the most common tools and how to use them. PDFs contains some nice exercises.
-	* http://www.tlpd.org - The Linux Documentation project. Look for the UNIX and Internet Fundamentals HOWTO. (Do you *really* know what happens when you turn on a PC?) 
+	* http://www.tldp.org - The Linux Documentation project. Look for the UNIX and Internet Fundamentals HOWTO. (Do you *really* know what happens when you turn on a PC?) 
+	* https://netfilter.org/documentation/HOWTO/networking-concepts-HOWTO.html - Elementary HOWTO about Networking. 
 
 
 Networking
 --------
-A good way to understand more about networking is two setup two computers: a server and a client. And the play around with the tools. The following tools and documentation are extremely useful 
+A good way to understand more about networking is two setup two computers: a server and a client. And the play around with the tools. The following tools and documentation are extremely useful.  
+
+Netcat
+~~~~~~
+Simple tool to open or connect to TCP or UDP ports and output data through these channels. Build and test proxies. Powerful for debugging. _Cryptcat_ is a similar tool, but with support for cryptography
+
+Sendip
+~~~~~~
+Create and send IP, TCP or UDP packages. You are able to edit any value within these packages. 
+
 
 Iptables
 ~~~~~~~~
-Although there is more abstract software to manage firewalls, like *ufw* on debian-based systems and *firewall-cmd* on redhat systems, Iptables will help you understand what actually happens during filtering, mangling or routing a package. https://www.frozentux.net/iptables-tutorial/iptables-tutorial.html has a structured approach in explaining _what happends when a package hits the firewall_.
+Although there is more abstract software to manage firewalls, like *ufw* on debian-based systems and *firewall-cmd* on redhat systems, Iptables will help you understand what actually happens during filtering, mangling or routing a package. https://www.frozentux.net/iptables-tutorial/iptables-tutorial.html has a structured approach in explaining _what happends when a package hits the firewall_. Pay extra attention to Network Address Translation. Here is another nice HOWTO: https://netfilter.org/documentation/HOWTO/NAT-HOWTO-5.html
+
+
 
 Virtual Private Networks
 ----