Understanding the Basic Firewall
Desktop Training - Fedora

At this point the basic firewall is complete and should be running.  Now it is time to gain some understanding of the basic rules that were created.

Lesson 2 / Lesson 4

The first thing you need to understand about the firewall you created is that applications communicate on a network using ports. A  port number is a 16-bit unsigned integer, thus ranging from 0 to 65535.  This means that there are a lot of choices on port numbers.  Applications are assigned specific ports numbers in this process so that network printing (IPP) is on port number 631, SSH is on port number 22, web servers are on port 80 and mail servers talk on port 25, for example. 

Second, services or applications always use a specific port for communication. This is why in the window you see a service and in the next column the port and protocol associated with that service.

The other thing is that applications use a specific protocol or language to communicate. In the example you will see the TCP ( Transgenic Control Protocol) and UDP (Unified Datago Protocol).  These protocols are different in how they function so each application may use either of these in the communication process.

Here is a list of the rules that were created in the Basic Firewall.

IPSec (/ah,/esp)
IPsec stands for Internet Protocol Security and provides a way for you to create a Virtual Private Network (VPN) from one location to another.  This is a method of encryption both the authentication and transmission of all data between the two points.   If you are not using a VPN you cna uncheck this option.  The most common use of this is when users will connect to their workplace computer using  a VPN.

Multicast DNS (mDNS)
Multicast DNS uses port 5353/UDP to automatically provide resolution and distribution of computer hostnames on a network.   Avahi, which works in conjunction with Multicast DNS,  allows applications to publish and discover services and hosts running on a local network without the need to condifure it.  This is an issue of convenience so you will probably want to keep it active.

Network Printing Client
The Internet Printing Protocol (IPP) allows for distributed printing as it finds and provides access to printers on a network using port 631/UDP.  If you are going to use CUPS for printing you will want to maintain this option.

Samba Client (137/UDP, 138/UDP)
Note this is the client not the server.  The client will allow a computer to connect to a Windows share if you are in a network where Linux and Windows machines co-exist.

These are the basic rules configured when you set up the basic firewall with the Wizard.  The main purpose it to provide you easy access to objects on your local network but also to protect you from anyone trying to connect to your computer.

Basic firewall