Network-Based IDS (NIDS)

A NIDS resides on computer or appliance connected to segment of an organization’s network and looks for signs of attacks. While examining packets, a NIDS looks for the attack patterns. Installed at specific place in the network where it can watch traffic going into and out of particular network segment. It can detect various types of attacks, but requires much complex configuration and maintenance program.

NIDS Signature Matching

To detect an attack, NIDSs look for attack patterns, which are done by using special implementation of TCP/IP stack.In this technique of protocol stack verification, NIDSs look for invalid data packets structure. In the application protocol verification, higher order protocols are examined for the improper use.

Advantages and Disadvantages of NIDSs

Advantages:
-Good network design and placement of NIDS can enable organization to use a few devices to monitor large network
-NIDSs are usually passive and can be deployed into existing networks with little disruption to normal network operations
-NIDSs not susceptible to direct attack and may not be detectable by attackers.

Disadvantages:
-Can become overwhelmed by network volume and fail to recognize attacks
-Require access to all traffic to be monitored
-Cannot analyze encrypted packets
-Cannot reliably ascertain if attack was successful or not
- Some forms of attack are not easily discerned by NIDSs, specifically those involving fragmented packets