In a stateful inspection firewall, data packets are captured by an inspection engine that is operating at the:

A.
Network or Transport Layer.

B.
Application Layer.

C.
Inspection Layer.

D.
Data Link Layer.

Explanation:
A stateful firewall filters traffic based on OSI Layer 3 (Network layer) and Layer 4 (Transport layer).Incorrect Answers:
B: A stateful firewall does not operate at the Application layer. It work at the Network or Transport Layer.
C: There is no inspection layer in the OSI model.
D: A stateful firewall does not operate at the Data link layer. It work at the Network or Transport Layer.

Conrad, Eric, Seth Misenar and Joshua Feldman, CISSP Study Guide, 2nd Edition, Syngress, Waltham, 2012,
p. 63