If you’re planning to take the SY0-501 exam, you should have a basic understanding of some of the more advanced network security concepts. This includes intrusion detection systems (IDSs) and intrusion prevention systems (IPSs).
For example, can you answer this practice test question?
Q. Attackers have recently launched several attacks against servers in your organization’s DMZ. You are tasked with identifying a solution that will have the best chance at preventing these attacks in the future. Which of the following is the BEST choice?
A. An out-of-band IPS
B. An in-band IPS
C. A passive IDS
D. An out-of-band IDS
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation are available at the end of this post.
IPS Versus IDS—Inline Versus Passive
Intrusion prevention systems (IPSs) are an extension of IDSs. Just as you can have both a HIDS and a NIDS, you can also have a HIPS and a NIPS, but a network-based IPS (NIPS) is more common. There are some primary distinctions of an IPS when compared with an IDS:
- An IPS can detect, react, and prevent attacks.
- In contrast, an IDS monitors and will respond after detecting an attack, but it doesn’t prevent them.
- An IPS is inline with the traffic. In other words, all traffic passes through the IPS and the IPS can block malicious traffic. This is sometimes referred to as in-band.
- In contrast, an IDS is out-of-band. It monitors the network traffic, but the traffic doesn’t go through the IDS. This is sometimes referred to as passive.
Most IDSs will only respond by raising alerts. For example, an IDS will log the attack and send a notification. The notification can come in many forms, including an email to a group of administrators, a text message, a pop-up window, or a notification on a central monitor. Some IDSs have additional capabilities allowing them to change the environment in addition to sending a notification.
For example, an IDS might be able to modify access control lists (ACLs) on firewalls to block offending traffic, close processes on a system that were caused by the attack, or divert the attack to a safe environment, such as a honeypot or honeynet. While this is sometimes referred to as an active IDS, this phrase can be misleading.
Specifically, the CompTIA Security+ objectives use the terms inline and in-band for an IPS and passive and out-of-band for an IDS.
The 601 Version of the Study Guide
The CompTIA Security+: Get Certified Get Ahead: SY0-601 Study GuideEach of the eleven chapters presents topics in an easy to understand manner and includes real-world examples of security principles in action.
You’ll understand the important and relevant security topics for the Security+ exam, without being overloaded with unnecessary details. Additionally, each chapter includes a comprehensive review section to help you focus on what’s important.
Over 300 realistic practice test questions with in-depth explanations will help you test your comprehension and readiness for the exam. The book includes:
- A 75 question pre-test
- A 75 question post-test
- Practice test questions at the end of every chapter.
Each practice test question includes a detailed explanation to help you understand the content and the reasoning behind the question. You’ll be ready to take and pass the exam the first time you take it.
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As a reminder, both IDSs and IPSs have protocol analyzer capabilities. This allows them to monitor data streams looking for malicious behavior. An IPS can inspect packets within these data streams and block malicious packets before they enter the network.
In contrast, a NIDS has sensors or data collectors that monitor and report the traffic. An active NIDS can take steps to block an attack, but only after the attack has started. The inline configuration of the IPS allows an IPS to prevent attacks from reaching the internal network.
As an example, the figure shows the location of two network-based IPSs (NIPS 1 and NIPS 2). All Internet traffic flows through NIPS 1, giving it an opportunity to inspect incoming traffic. NIPS 1 protects the internal network by detecting malicious traffic and preventing attacks from reaching the internal network.
NIPS used to detect and prevent attacks
NIPS 2 is protecting an internal private network. As an example, imagine that Homer needs to manage some equipment within a supervisory control and data acquisition (SCADA) network in the nuclear power plant. The SCADA equipment is in the private network. The firewall next to NIPS 2 can have rules that allow traffic from Homer’s computer into the network, but block all other traffic. NIPS 2 will then inspect all the incoming traffic and block malicious traffic.
This might seem like overkill, but many advanced persistent threats (APTs) have successfully installed remote access Trojans (RATs) onto internal systems through phishing or malware attacks. Once the RAT is installed, attackers can now attack from within. If an attacker began launching attacks on the private network from Homer’s system, the firewall wouldn’t block it. However, the NIPS will prevent this attack from reaching the private network.
Notice that each IPS is placed on the edge of the protected network. NIPS 1 is placed on the edge of the network between the Internet and the demilitarized zone (DMZ). NIPS 2 is on the edge of the SCADA network between it and the intranet. This placement ensures that the NIPS can inspect all traffic going into the network.
Q. Attackers have recently launched several attacks against servers in your organization’s DMZ. You are tasked with identifying a solution that will have the best chance at preventing these attacks in the future. Which of the following is the BEST choice?
A. An out-of-band IPS
B. An in-band IPS
C. A passive IDS
D. An out-of-band IDS
Answer is B. The best solution of the given choices is an in-band intrusion prevention system (IPS). Traffic goes through the IPS and the IPS has the best chance of preventing attacks from reaching internal systems.
An IPS is in-band not out-of-band.
An intrusion detection system (IDS) is passive and not in-band, so it can only detect and react to the attacks, not block them.
See Chapter 4 of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide for more information on IDSs and IPSs.
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