Which of the following is not a major processing mode category for firewalls?

Firewalls can be classified according to their major processing modes. These are:

• Pass-through mode: Firewalls that allow all traffic, including incoming connections from the Internet, through them;
  
  
• Application layer firewall: A firewall that sits at the application layer of the OSI model and controls which packets are passed on to higher levels of the network where they can be processed by applications;
  
  
• Network layer firewall: A firewall that sits at the network layer of the OSI model and blocks or allows packets based on their destination IP addresses and port numbers.