In computing, a firewall can mean one of two things—it can refer to a network appliance that has, as one of its functions, the ability to filter incoming and outgoing traffic (hardware) or a service running on a computer that has the ability to filter traffic (software). In this chapter, we will be using the latter sense of the term. We will be focused primarily on the ability to use pfSense as a means of filtering traffic on your network, which is likely to be one of the primary functions pfSense's performs on your network, unless you have a dedicated firewall appliance. 

In previous chapters, we couldn't avoid talking about firewall rules, and in this chapter we will cover firewall rules and rule methodology in greater depth. We will also cover several services that are part of pfSense's core firewall functionality, such as aliases and scheduling. 

Completing this chapter should enable you to master the following topics:

• Firewall fundamentals
• Firewall best practices
• Firewall rules and methodology
• Scheduling
• Aliases
• Virtual IPs
• Troubleshooting firewall rules