Network-based Intrusion Detection systems:

A.
commonly reside on a discrete network segment and monitor the traffic on that network segment.

B.
commonly will not reside on a discrete network segment and monitor the traffic on that network segment.

C.
commonly reside on a discrete network segment and does not monitor the traffic on that network segment.

D.
commonly reside on a host and monitor the traffic on that specific host.

Explanation:
A network – based IDS (Intrusion Detection systems) watches for questionable activity occurring on the network
medium by inspecting packets and observing network traffic patterns.
Incorrect Answers:
B: The networked-based ISD must be present on the network segment it is monitoring.
C: The purpose of an Intrusion Detection system is to monitor the traffic.
D: A host-based, not a network-based, IDS watches for questionable activity on a single computer system.

Stewart, James M., Ed Tittel, and Mike Chapple, CISSP: Certified Information Systems Security Professional
Study Guide, 5th Edition, Sybex, Indianapolis, 2011, p. 54