Why do application proxy gateways spend more time on each packet?

1. A proxy does not merely check headers. 2. It reads and interprets the whole thing. 3. Because of the full packet awareness of application proxy gateways, the firewall spends much more time reading each packet. 4. So the answer is full packet awareness. _Source: NIST SP 800-41 Rev. 1, 'Guidelines on Firewalls and Firewall Policy'_