Which of the following layers of the ISO/OSI model do packet filtering firewalls operate at?
A.
Application layer
B.
Session layer
C.
Network layer
D.
Presentation layer
Explanation:
Packet filtering firewalls work at the network level of the OSI model, or the IP layer
of TCP/IP. These firewalls are normally part of a router, which is a device that receives and
forwards packets to networks. “In a packet filtering firewall each packet is compared to a set of
criteria before it is forwarded. Depending on the packet and the criteria, the firewall can drop the
packet, forward it, or send a message to the originator.” The criteria used to evaluate a packet
include source, destination IP address, destination port, and protocol used. These types of
firewalls are low in cost and don’t have much of an impact on the network’s performance.