Chapter 7 Firewall : Firewall concepts
  
Firewall concepts
There are a number of concepts that are consistent throughout the firewall industry and having a solid grasp of these ideas and terms can give you a better idea of what your FortiGate firewall is capable of and how it will be able to fit within your networks architecture.
This chapter describes the following firewall concepts:
What is a Firewall?
IPv6
NAT
How Packets are handled by FortiOS
FortiGate Modes
Quality of Service
Interfaces and Zones