Intrusion Detection System (IDS) : A Complete Guide



One of the most essential aspects of system, network management and security is protecting your network against infiltration. A hostile attacker breaking into your network can cause serious problems for your business, including downtime, data breaches, and a loss of customers.

Software or device called an intrusion detection system (IDS) keeps track of all network traffic, both inbound and outgoing, continually scans the data for deviations from the norm and notifies the administrator of any suspicious activity. The threat is then eliminated when an administrator checks alarms.

In this extensive overview, we’ll cover all you need to know about IDS, including what an intrusion detection system is, how network intrusion operates, and how to spot network intrusion.

What is an IDS?

An IDS, for instance, may examine the information carried by network traffic to check for the presence of known malware or other dangerous material. If it finds this kind of danger, it alerts your security team so they can look into it and take the appropriate action. To stop an attack from taking over the system, your team must respond immediately after receiving the alarm.

These systems frequently utilize a switching port analyzer (SPAN) or test-access port (TAP) to examine a copy of the inline data traffic to ensure that an IDS doesn’t affect network performance. They do not, however, prevent threats from entering the network as intrusion prevention systems do.

Whether an IDS application is installed or a physical device is put up, the system can:

  • Analyze the patterns of attacks in network packets.
  • Observe how users behave.
  • Determine any unusual traffic patterns.
  • Make sure that user and system behavior does not violate security guidelines.

The security team can additionally benefit from the information from an intrusion detection system by:

  • Check the network for weaknesses and incorrect setups.
  • Analyze the files’ and systems’ integrity.
  • Improve the controls and incident response processes.
  • Analyze the number and kind of online threats that are affecting the network.

Aside from cybersecurity advantages, an IDS also aids in regulatory compliance. Improved logging and visibility guarantee that network activities comply with all applicable laws.

Intruders can be kept away from vital data and resources by using other security measures in addition to IDSes, as detailed in our article on several forms of network protection.

Objectives of Intrusion Detection System

Modern cyberdangers cannot be adequately protected by a firewall alone. Malicious material is frequently sent via legitimate transmission, such as email or web traffic. An IDS gives the capacity to examine the information in these communications and find any potential malware.

An IDS’s main objective is to find anomalies before hackers succeed in their mission. When a threat is identified, the IDS notifies the IT team and provides them with the following information about the risk:

  • The intrusion’s origin IP address.
  • Addresses to the target and victim.
  • The kind of danger.

An intrusion detection system observes intruders and identifies them as a secondary objective.

  • What assets an attacker attempts to access.
  • How hackers attempt to get around security measures.
  • What kinds of cyberattacks do the invaders launch.

This information may be used to strengthen the network security strategy by the company’s security operations center (SOC) and analysts.

An intrusion detection system’s two main purposes are anomaly detection and reporting. Some detection systems can, however, take action in response to malicious behavior, such as immediately banning an IP address or preventing access to private data. Intrusion prevention systems are those with these reaction capabilities (IPSs).

Learn how cautious businesses keep networks secure from illegal access and misuse by reading about network security fundamentals.

The Simplest Way to Locate Your Network’s SSID

This tutorial will guide you through the process of discovering the SSID (Service Set Identifier) of your network. The SSID is the unique name that identifies your wireless network, allowing you to connect to the internet. With our step-by-step instructions, you’ll be able to quickly find and understand the network SSID on your device.

Process of Intrusion Detection Systems

An IDS observes all network traffic to and from all devices. The system, which serves as a secondary filter for malicious packets behind a firewall, mainly scans for two suspicious indicators:

  • Signs of well-known assaults.
  • Deviations from routine behavior

To identify threats, an intrusion detection system often uses pattern correlation. Using this technique, an IDS may examine network packets against a database of known cyberattack signatures. The most typical assaults that a pattern correlation-based IDS may detect include:

  • Malware (worms, ransomware, trojans, viruses, bots, etc.).
  • Assaults that send packets to the network to collect information on open or closed ports allowed traffic kinds, running hosts, and software versions.
  • Asymmetric routing that uses separate entrance and exit routes to transmit a malicious packet and get around security measures
  • Buffer overflow attacks that switch malicious executable files for the database content.
  • Assaults on a certain protocol that are protocol-specific (ICMP, TCP, ARP, etc.).
  • Network overloading traffic breaches like DDoS attacks cause the network to overflow.

The system flags the problem and sounds the alert as soon as an IDS detects an abnormality. The alarm might be as straightforward as a notation in an audit log or as critical as a communication to an IT administrator. The team then investigates the issue and determines its primary cause.

Types of Intrusion Detection Systems

Based on where the security team installs them, there are two primary types of IDSes:

  • Network intrusion detection system (NIDS).
  • Host intrusion detection system (HIDS).

We can also distinguish between two groups based on how an intrusion detection system picks up on suspicious activity:

  • A signature-based intrusion detection system (SIDS).
  • An anomaly-based intrusion detection system (AIDS).

You can utilize either a HIDS or NIDS, or you can rely on both of the fundamental IDS types, depending on your use case and financial constraints. As many teams build up a hybrid system with SIDS and AIDS capabilities, the same is true of detection models.

It would be best if you comprehend the variations among IDS kinds and how they work together before you decide on an approach. Let’s examine the four primary IDS kinds, their benefits and drawbacks, and appropriate usage scenarios.

Network Intrusion Detection System (NIDS)

A network-based intrusion detection system tracks and examines every network device traffic. Typically at data chokepoints, a NIDS operates from a strategic location (or points, if you deploy several detection systems) within the network.

Advantages of a NIDS

  • Protects the network as a whole with IDS.
  • A few carefully positioned NIDS can monitor an enterprise-sized network.
  • A non-active device that doesn’t reduce network performance or availability.
  • Quite simple to conceal from thieves and protect.
  • Includes areas of networks where traffic is most at risk.

Downsides of a NIDS:

  • Costly to set up.
  • A NIDS system may have low specificity and the sporadic occurrence of an undetected breach if it is required to monitor a large or active network.
  • Threat detection in encrypted traffic can be challenging.
  • Usually not the best match for switch-based networks.

Host intrusion detection system (HIDS)

A HIDS monitors network traffic and system logs to and from a single device while operating from a defined endpoint.

Regular snapshots—file sets that record the current state of the whole system—are the foundation of this sort of IDS protection. The IDS looks for missing or changed files or settings when the system takes a snapshot and compares it to the prior state.

Advantages of HIDS

  • Provides extensive insight into the host device and its operations (changes to the configuration, permissions, files, registry, etc.).
  • A strong backup line of defense against a malicious packet that NIDS missed.
  • Excellent at identifying packets inside the company, such as unwanted file modifications from a system console.
  • Effective in finding and preventing breaches in software integrity.
  • Due to fewer packets, it is more effective than NIDS  in decrypting encrypted communication.
  • Much less expensive than putting up a NIDS

Downsides of HIDS

  • The system monitors limited visibility since just one device.
  • Less context is accessible for decision-making.
  • Large businesses find it challenging to maintain since a team must configure and handle each host’s information.
  • A NIDS is less noticeable to attackers.
  • Not good at identifying network scans or other attacks that target the whole network for monitoring.

A signature-based intrusion detection system (SIDS)

A SIDS keeps track of packets moving through a network and evaluates them against a database of acknowledged attack signatures or characteristics. This prevalent IDS security type searches for certain patterns, such as byte or instruction sequences.

Advantages of SIDS

  • Effective against intruders utilizing recognized attack signatures.
  • Helpful in identifying low-tech assault tries.
  • Effective at keeping track of network traffic coming in.
  • Can effectively handle a lot of network traffic.

Downsides of SIDS

  • A breach cannot be identified without a precise signature in the threat database.
  • A clever hacker can change an attack to avoid matching recognized signatures, for example, by changing lowercase characters to uppercase or a symbol to its character code.
  • Need frequent threat database updates to keep the system current with emerging threats.

An anomaly-based intrusion detection system (AIDS)

An AIDS tracks current network activity and examines trends compared to a reference point. Instead of focusing on specific data patterns, it extends beyond the attack signature concept to identify harmful behavior patterns.

This kind of IDS establishes a baseline of expected system behavior (trust model) using machine learning regarding bandwidth, protocols, ports, and device utilization. The system may then assess any novel activity against validated trust models to find undiscovered assaults that signature-based IDS cannot recognize.

For instance, the attempt to access the website’s backend by someone in the sales department may not be a sign of SIDS.

However, a person attempting to access a sensitive system for the first time is a reason for inquiry for an anomaly-based setup.

Advantages of AIDS

  • Can spot indicators of unique risks and undiscovered attack kinds.
  • It develops a precise behavioral model using AI and machine learning.

Downsides of AIDS

  • Difficult to handle
  • More processing power is needed than with a signature-based IDS.
  • Alarm volume might overwhelm administrators.
  • Our post on the best network security tools lists the best choices available and aids in building the ideal security tool stack.

IDS Advantages and Disadvantages

The crucial understanding of network activity provided by using an IDS is its evident strength. Early identification of odd behavior lowers the possibility of cyberattacks and promotes overall network health.

An excellent method to improve security is to use an IDS to safeguard a network. When used in conjunction with a strong firewall and anti-malware application, an IDS guarantees the team:

  • It keeps one step ahead of most cyber issues, whether they result from bad actors, accidents, or mistakes.
  • Does not have to go through hundreds of system logs to find important information.
  • Capable of effectively enforcing the network-level security standards of the firm.

IDSes (and even IPSes) are getting more affordable and manageable, so SMBs with limited resources and IT professionals may rely on this tactic. Despite all the advantages, IDSes nonetheless face a few particular difficulties:

  • The key to a successful attack is avoiding an IDS. Hence hackers frequently target these systems.
  • Malicious activity in encrypted communications could be hard to spot.An IDS may perform worse in a network with a lot of traffic.
  • Even the greatest system may struggle to spot warning signals of a fresh attack.
  • IDS only tracks east-west travel; it does not track north-south traffic.

Avoiding errors is an IDS’s hardest issue since even the finest system can make mistakes:

  • Alert the public to an event that is not an assault (a false positive).
  • Not sounding the alert when a threat is there (a false negative).

The IT staff will trust the IDS’s warnings less if there are too many false positives. However, false negatives indicate that hostile packets are entering the network undetected. Therefore, an oversensitive IDS is always preferable.

In contrast to an internal IDS, managed detection response (MDR) allows you to trust a vendor to secure your network devices and data.

Best Practices for IDS

Make sure your strategy adheres to the following best practices once you have determined the IDS type and detection model you must put up:

  • Teach IT personnel. Ensure the team installing the IDS is well aware of your device inventory and the function of each machine.
  • Choose a baseline. Establish a baseline so you know what is on your network so your IDS can distinguish between typical and deviant behavior. Remember that the traffic that each network transports vary. A clear starting baseline definition aids in avoiding false positive and false negative results.
  • IDS Implementation. Install the IDS at the greatest point of sight to avoid data overloading the system. Place the IDS behind the firewall, at the very edge of your network. If you need to handle intra-host traffic, install many IDSes around the network. The network and security objectives determine the best installation solution and where to implement it.
  • IDS should be network-tuned. You should change the IDS’s default settings only when it makes sense for the network. Configure the IDS to support all network-connected hardware, software, ports, protocols, and security points. You build a strong foundation for detection by customizing the configuration to fit your network infrastructure.
  • Establish Stealth Mode. To make the system challenging to identify hostile actors, configure the IDS to operate in stealth mode. Ensuring the IDS has two network interfaces—one for the network and one for creating alerts—is the simplest method to do this. The monitored interface should be the only input used by the IDS.
  • Examine the IDS. Test the IDS to make sure it recognizes possible threats and reacts appropriately to them. Utilize test datasets or, better yet, hire security experts to do a penetration test (pen test). Run these checks often to ensure everything is functioning as it should. Develop your testing strategy over time to stay up with changes in the possible forms of assaults.
  • Negatives and False Positives must be balanced. Don’t over-tune your IDS or set it incorrectly to avoid producing false positives or negatives. A surplus of either can overburden your IT and security professionals and possibly increase the likelihood of an attack on your company. To increase the effectiveness and manageability of detections, combine NIDS configurations with network segmentation.
  • Investigate incidents and take action. Create a prepared incident response strategy. This strategy must incorporate trained security people who can react swiftly and decisively while causing the least disturbance to regular business activities and harm to your firm. Set up the proper controls and adhere to the specified processes if your business has to comply with industry standards like HIPAA, GDPR, or SOC 2. Think about introducing a second platform for threat analysis once the IDS sounds the alert.
  • Regularly update the threat database. Your team should update the threat database as soon as the IDS is operational to maintain the system’s effectiveness. Make sure all your IDSes and threat databases adhere to the zero-trust security paradigm.

All About Intrusion Prevention System (IPS) and 9 Best IPS Tools

To stop assaults at the network level, the IPS technologies may easily be linked with other tools used in network security. We will learn more about this in this chapter.


A high-quality IDS (or IPS) is essential for network security to remain at acceptable levels. An IDS can miss certain possible risks since it only identifies threats. Therefore, preventing attacks and defending your company against them is insufficient.

Instead, an IDS is a component of your overall security plan. You need to make sure your staff, who are your first line of defense, know how to protect your company, information, and assets and have the appropriate security technologies in place. An efficient program for raising cybersecurity awareness is the first line of defense. In exchange, they’ll have more faith in their ability to respond to them, reduce dangers to your company and your clients, and react appropriately.

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