Firewall-Configuration-and-Common-Misconfigurations.md

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 Firewalls are a key component of a secure network. At a basic level, a firewall serves as a filter between a network and the Internet other other external networks. Just like an air or water filter keeps unsafe particles from polluting an environment, a firewall keeps potentially malicious activity from entering or exiting a network. In an environment with several devices connecting to the internet, a firewall should be placed at every Internet connection.  
 
+![Palo Alto Firewall Rules](https://knowledgebase.paloaltonetworks.com/servlet/rtaImage?eid=ka10g000000U2oY&feoid=00N0g000003VPSv&refid=0EM0g000001AeS4)
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+The above figure shows the web GUI for a Palo Alto Firewall. In this image, the various policies for the firewall are being displayed.
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 When configuring a firewall for a network, the administrator will set a variety of *rules*, or policies that determine what traffic should be permitted into or blocked from the network. There are multiple ways that firewall rules can help filter traffic, and the following three methods are the most common: packet filtering firewalls, application-level firewalls, and stateful inspection firewalls. Other types of firewalls include unified threat management firewalls, next-generation firewalls, and virtual firewalls.   
 
 ## Packet Filtering Firewalls
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 * General Firewall Information
   * How Firewalls Work: https://computer.howstuffworks.com/firewall1.htm
   * What Are Firewall Rules: https://www.algosec.com/what-are-firewall-rules/
+  * Palo Alto Policy Fundamentals: https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClWZCA0
 * Packet Filtering Firewalls
   * Image Source: https://content.iospress.com/articles/argument-and-computation/aac008
 * Application-Layer Firewalls