Packet filtering firewalls operate at:

A.
The Application layer of the OSI model

B.
The Session layer of the OSI model

C.
The Network layer of the OSI model

D.
The Presentation layer of the OSI model

Explanation:
Packet filtering firewalls are routing devices that include access
control functionality for communication sessions and system addresses. This type of
firewall can operate at either the Network or Transport layer of the OSI model.