Redefining Next Generation Firewalls

When the first firewalls were developed and deployed, their primary role was to act as sentinels monitoring traffic moving into, and sometimes out of the network. These devices would look at packets, network addresses, and ports to determine if data should be allowed through or blocked. A good analogy is airline travel. In the first few iterations of the firewall, data was simply checked to see if it had a ticket, and if its credentials were in order it were allowed to board the plane.

https://blog.fortinet.com/2017/09/28/redefining-next-generation-firewalls