Intrusion Detection System Threshold

Posted by in Security+ | 0 comments

An intrusion detection system can only detect an attack. It cannot prevent attacks. The primary purpose of IDS is to know if the system is under attack.  If you’re planning on taking the Security+ exam, you should have a basic understanding of IDS methods and threshold.

For example, can you answer this question?

Q. Administrators have noticed an increased workload recently. Which of the following can cause an increased workload from incorrect reporting?

A. False negatives

B. False positives

C. Separation of duties

D. Signature-based IDSs

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Full Security+ Course

Full Security+ Course Now Available

Helping you Pass the First Time

Online access includes all of the content from the

CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide

  • Introduction
  • About the exam (including types of questions and strategies for performance-based questions)
  • 100 question pre-assessment exam
  • Mastering Security Basics (full content from Chapter 1 of the study guide including the exam topic review and 20 practice test questions)
  • Exploring Control Types and Methods (full content from Chapter 2 of the study guide including the exam topic review and 20 practice test questions)
  • Understanding Basic Network Security (full content from Chapter 3 of the study guide including the exam topic review and 20 practice test questions)
  • Securing Your Network (full content from Chapter 4 of the study guide including the exam topic review and 20 practice test questions)
  • Securing Hosts and Data (full content from Chapter 5 of the study guide including the exam topic review and 20 practice test questions)
  • Understanding Malware and Social Engineering (full content from Chapter 6 of the study guide including the exam topic review and 20 practice test questions)
  • Identifying Advanced Attacks (full content from Chapter 7 of the study guide including the exam topic review and 20 practice test questions)
  • Managing Risk (full content from Chapter 8 of the study guide including the exam topic review and 20 practice test questions)
  • Preparing for Business Continuity (full content from Chapter 9 of the study guide including the exam topic review and 20 practice test questions)
  • Understanding Cryptography (full content from Chapter 10 of the study guide including the exam topic review and 20 practice test questions)
  • Exploring Operational Security (full content from Chapter 11 of the study guide including the exam topic review and 20 practice test questions)
  • 100 question post-assessment exam
  • Security+ Acronyms

Get the Full Security+ Course Here

 Full Security+ Course Now Available


Test your readiness with these quality materials

Random 100-question tests

Random practice tests from the all of the practice test questions in the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide. All questions include explanations so you'll know why the correct answers are correct, and why the incorrect answers are incorrect.

34 Simulated Performance-based Questions

Eight sets of performance-based questions with multiple questions in each set. These questions help you understand and prepare for performance based questions.

22 Realistic Performance-based Questions

Two new sets of performance-based questions with a total of 22 questions. These new questions use a new testing engine that includes realistic drag and drop, matching, sorting, and fill in the blank questions.

Flashcard Set

  • 273 Security+ Flashcards to reinforce key testable concepts
  • 280 Security+ acronyms flashcards to help you master the required acronyms
  • 204 Security+ Remember This slides

Audio - SY0-401 Security+ Remember This Audio Files

Learn by Listening. Over one hour and 15 minutes of audio (MP3 downloads.)

Audio - SY0-401 Security+ Question and Answer Audio Files

Learn by Listening. Over three hours hour and 15 minutes of audio (MP3 downloads.)

Bonus #1

Audio from the end of chapter reviews from each of the chapters in the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide. Over one hour and 15 minutes of additional audio.

Bonus #2

Subnetting mini-tutorial that will help you answer two key question types:
  • Identify how many hosts a subnet supports
  • Identify valid IP addresses within a subnet

Bonus #3 

Access the study materials for a total of 60 days because sometimes life happens.

Get the Full Security+ Course Here

Using Data Sources and Trends

Any type of intrusion detection system will use various raw data sources to collect information on activity. This includes a wide variety of logs, such as firewall logs, system logs, and application logs. These logs can be analyzed to provide insight on trends. These trends can detect a pattern of attacks and provide insight into how to better protect a network.

Many IDSs have the capability to monitor logs in real time. Each time a system records a log entry, the IDS examines the log to determine if it is an item of interest or not. Other IDSs will periodically poll relevant logs and scan new entries looking for items of interest.

Get Certified Get Ahead

IDSs Reporting

IDSs report on events of interest based on their settings. All events aren’t attacks or actual issues, but instead, they provide a report indicating an event might be an alert or an alarm. Administrators investigate to determine if it is valid. Some systems consider an alarm and an alert as the same thing. Other systems use an alarm for a potentially serious issue, and an alert as a relatively minor issue. The goal in these latter systems is to encourage administrators to give a higher precedence to alarms than alerts.

The actual reporting mechanism varies from system to system and in different organizations. For example, one IDS might write the event into a log as an alarm or alert, and then send an email to an administrator account. In a large network operations center (NOC), the IDS might send an alert to a monitor easily viewable by all personnel in the NOC.

False Positives Versus False Negatives

IDSs are susceptible to both false positives and false negatives. A false positive is an alert or alarm on an event that is nonthreatening, benign, or harmless. A false negative is when an attacker is actively attacking the network, but the system does not detect it. Neither is desirable, but it’s impossible to eliminate both. Most IDSs trigger an alert or alarm when an event exceeds a threshold.

Intrusion detection system

Consider the classic SYN flood attack, where the attacker withholds the third part of the TCP handshake. A host will send a SYN packet and a server will respond with a SYN/ACK packet. However, instead of completing the handshake with an ACK packet, the attacking host never sends the ACK, but continues to send more SYN packets. This leaves the server with open connections that can ultimately disrupt services.

If a system receives one SYN packet without the accompanying ACK packet, is it an attack? Probably not. This can happen during normal operations. If a system receives over 1,000 SYN packets from a single IP address in less than 60 seconds, without the accompanying ACK packet, is it an attack? Absolutely.

With this in mind, administrators set the threshold to a number between 1 and 1,000 to indicate an attack. If administrators set it too low, they will have too many false positives and a high workload as they spend their time chasing ghosts. If they set the threshold too high, actual attacks will get through without administrators knowing about them.

CompTIA Security+ Study Guide (SY0-401)

The 401 Version of the Study Guide is Now Available

SY0-401 Study GuideThe CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide is an update to the top-selling SY0-201 and SY0-301 study guides, which have helped thousands of readers pass the exam the first time they took it.

CompTIA Authorized Quality Content (CAQC)After a comprehensive review by ProCert Labs, the SY0-401 version has been certified as CompTIA Approved Quality Content (CAQC) and covers every aspect of the SY0-401 exam.

It includes the same elements readers raved about in the previous two versions.

Each 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.


Click for Free Preview


Over 400 realistic practice test questions with in-depth explanations will help you test your comprehension and readiness for the exam. The book includes:

  • A 100 question pre-test
  • A 100 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.

If you plan to pursue any of the advanced security certifications, this guide will also help you lay a solid foundation of security knowledge. Learn this material, and you’ll be a step ahead for other exams. This SY0-401 study guide is for any IT or security professional interested in advancing in their field, and a must read for anyone striving to master the basics of IT security.

Kindle edition also available.

Most administrators want to know if their system is under attack. That’s the primary purpose of the IDS. However, an IDS that constantly cries “Wolf!” will be ignored when the real wolf attacks. It’s important to set the threshold high enough to reduce the number of false positives, but low enough to alert on any actual attacks.

There is no perfect number for the threshold. Administrators adjust thresholds in different networks based on the network’s activity level and their personal preferences.

Remember this

A high incidence of false positives increases the administrator’s workload. Administrators often set the IDS threshold high enough that it minimizes false positives but low enough that it does not allow false negatives.


Security+ Practice Test Questions

SYO-401 Practice Test Questions Now Available

Over 440 realistic Security+ practice test questions

All questions include explanations so you'll know why the correct answers are correct,

and why the incorrect answers are incorrect.

Pass the Security+ Exam

the First Time You Take It

Multiple quiz formats to let you use these questions based on the way you learn.
  • Learn mode - randomized. View each of the questions in random order. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.
  • Learn mode - not randomized. View each of the questions in the same order. Use this if you want to make sure that you see all of the questions. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.
  • Test mode - randomized. View each of the questions in random order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.
  • Test mode - not randomized. View each of the questions in the same order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.
  • Test mode - 100 random questions. View 100 random questions from the full test bank similar to how the Security+ exam has a potential maximum of 100 multiple choice questions. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.

Get the full bank of Security+ Practice Test Questions Here

 SYO-401 Practice Test Questions Now Available


INCLUDES QUESTIONS TO HELP YOU PREPARE

FOR THE NEW PERFORMANCE BASED QUESTIONS 

Bonus - Performance Based Questions

Additional Security+ questions to help you prepare for the new performance based questions. These are included with the full bank of Security+ practice test questions and are divided into different sections. For example, you'll have access to the following links:

- Performance Based Question - Set 1

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of security to mobile devices and servers in a data center. You'll then have two questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 2

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of attacks with the name of the attack type. You'll then have five questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 3

You'll see a graphic showing a network with computers and servers separated by a firewall. The firewall is used to control traffic between the computers and users using rules within an access control list (ACL).  You'll have three questions that test your knowledge and ability to correctly identify the relevant components of the rule. The incorrect answers and explanation provide you with insight into how to correctly answer this type of question on the actual exam.

- Performance Based Question - Set 4

You'll see a graphic explaining what you might be required to do on the actual exam related to what a forensic analyst would do during an investigation. You'll then have two questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 5

You'll see a graphic explaining what you might be required to do on the actual exam to match protocols and ports. You'll then have seven questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 6

You'll see a list of security controls along with a graphic showing devices and locations within an organization, along with instructions on what you might be required to do on the actual exam to match the controls with the devices and locations. You'll then have four questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 7

You'll see a list of authentication methods and authentication factors along with instructions on what you might be required to do on the actual exam to match the authentication methods with the authentication factors. You'll then have six questions that test your knowledge and ability to correctly answer the questions. This set also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 8

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of attacks with the name of the attack type. You'll then have five questions that test your knowledge and ability to correctly answer the questions. This is similar to Set 2 but expands on the possibilities. The set also includes a link to a page showing the end solution for the overall performance based question simulation.

New - Performance Based Question - Set 9

New questions recently added using a different testing engine. See a demo here. This set includes drag and drop and matching questions on ports.

New - Performance Based Question - Set 10

A random set of 20 performance-based questions using drag and drop, matching, sorting, and fill in-the blank. This set includes performance-based questions on RAID.

Get the full bank of Security+ Practice Test Questions Here

Get the full bank of Security+ Practice Test Questions

Q. Administrators have noticed an increased workload recently. Which of the following can cause an increased workload from incorrect reporting?

A. False negatives

B. False positives

C. Separation of duties

D. Signature-based IDSs

Answer is B. False positives can cause an increased workload because they falsely indicate an alert has occurred.

A false negative doesn’t report an actual attack, so it doesn’t increase the workload because administrators are unaware of the attack.

Separation of duties ensures a single person can’t control an entire process, so it is unrelated to increased workload.

Signature-based intrusion detection systems (IDSs) don’t necessarily cause an increased workload unless they have a high incidence of false positives.

See Chapter 4 of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide for more information on detection methods.

You may like to view other blog posts related to IDS:

IDS Detection Methods

IDS Versus IPS

Leave a Comment

CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide

Subscribe To Our Newsletter

Join our mailing list and get a free excerpt of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide.  This excerpt includes the introduction and Chapter 1. 

You have Successfully Subscribed!

Get Certified Get Ahead is a participant in the Amazon Services LLC Associates Program,
an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.

Copyright © 2015 Get Certified Get Ahead. All Rights Reserved.