The two most common implementations of Intrusion Detection are Network-based and Host-based.

IDS can be implemented as a network device, such as a router, switch, firewall, or dedicated device monitoring traffic, typically referred to as network IDS (NIDS).

The" (IDS) "technology can also be incorporated into a host system (HIDS) to monitor a single system for undesirable activities. "

A network intrusion detection system (NIDS) is a network device .... that monitors traffic traversing the network segment for which it is integrated." Remember that NIDS are usually passive in nature.

HIDS is the implementation of IDS capabilities at the host level. Its most significant difference from NIDS is that related processes are limited to the boundaries of a single-host system. However, this presents advantages in effectively detecting objectionable activities because the IDS process is running directly on the host system, not just observing it from the network.

Reference(s) used for this question:

Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 3649-3652). Auerbach Publications. Kindle Edition.