IDSIntrusion is a attack on information assets in which instigator attempts to gain entry into or disrupt normal system with harmful intent Incident response is an identification of, classification of, response to, and recovery from an incident. Intrusion prevention comprises of activities that seek to deter an intrusion from occurring. Intrusion detection consists of procedures and systems created and operated to detect the system intrusions. Intrusion reaction encompasses actions an organization undertakes when intrusion event can be detected. Intrusion activities of finalize restoration of operations to a normal state. IDS detect a violation of its configuration and activate alarm. Many IDSs enable administrators to configure systems to directly notify them of trouble by means of e-mail or pagers. Systems can be configured to notify an external security service organization of a break-in. The figure given below illustrates the basic functionalities of intrusion detection system.