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Intrusion Detection System

: Intrusion detection system (IDS) is a device or software application that monitors network or system activities for malicious activities or policy violations and produces reports to a management station. IDS come in a variety of “flavors” and approach the goal of detecting suspicious traffic in different ways.

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Intrusion Detection Systems help information systems prepare for, and deal with attacks. They accomplish this by collecting information from a variety of systems and network sources, and then analyzing the information for possible security problems.


Intrusion detection provides the following:

  • · Monitoring and analysis of user and system activity
  • · Auditing of system configurations and vulnerabilities
  • · Assessing the integrity of critical system and data files
  • · Statistical analysis of activity patterns based on the matching to known attacks
  • · Abnormal activity analysis · Operating system audit There are three main components to the Intrusion detection system
  • · Network Intrusion Detection system (NIDS) – performs an analysis for a passing traffic on the entire subnet.


Works in a promiscuous mode, and matches the traffic that is passed on the subnets to the library of knows attacks. Once the attack is identified, or abnormal behavior is sensed, the alert can be send to the administrator. Example of the NIDS would be installing it on the subnet where you firewalls are located in order to see if someone is trying to break into your firewall




  • · Network Node Intrusion detection system (NNIDS) – performs the analysis of the traffic that is passed from the network to a specific host. The difference between NIDS and NNIDS is that the traffic is monitored on the single host only and not for the entire subnet. The example of the NNIDS would be, installing it on a VPN device, to examine the traffic once it was decrypted. This way you can see if someone is trying to break into your VPN device


  • · Host Intrusion Detection System (HIDS) – takes a snap shot of your existing system files and matches it to the previous snap shot. If the critical system files were modified or deleted, the alert is sent to the administrator to investigate. The example of the HIDS can be seen on the mission critical machines, that are not expected to change their configuration