Review AP Cybersecurity Unit 3 to understand how networks are attacked and how defenders protect them. This unit covers ARP poisoning, DoS attacks, firewalls, network segmentation, and detection tools like NIDS, NIPS, and SIEM.
Use the topic guides, key terms, and practice questions available for every topic in this unit to build a complete picture of network security.
Networks connect devices and move data, which creates opportunities for adversaries to intercept, redirect, or flood that traffic. Unit 3 builds a complete picture of how those attacks work and what defenders do to stop them.
Adversaries exploit protocols like ARP and DNS to redirect traffic, flood switches with fake MAC addresses, or launch DoS attacks that overwhelm a network. Understanding the mechanism of each attack is the foundation for choosing the right defense.
Segmentation divides a network into isolated zones using screened subnets (DMZs), IP subnetting, and VLANs. Firewalls sit at each boundary and enforce ACL rules that permit or deny traffic based on IP address, port, protocol, or application.
NIDS alerts on suspicious traffic, NIPS can block it automatically, and SIEM aggregates log data from across the network. Detection methods trade off speed, cost, and false positive rate depending on whether they use signature-based or anomaly-based approaches.
No single control secures a network. Unit 3 shows how managerial policies, physical and wireless controls, segmentation, firewall rules, and detection tools layer together so that a failure in one layer does not expose the entire network.
Covers ARP poisoning, MAC spoofing, MAC flooding, DNS poisoning, and DoS attacks. Includes how to assess vulnerability risk using the CIA triad and automated vulnerability scanners.
Covers router, switch, and VPN security policies as managerial controls, plus wireless access point settings: disabling beacon frames, controlling signal strength, requiring WPA3, and enabling MAC filtering.
Covers screened subnets (DMZs), IP subnetting, VLANs, and port security. Explains how segmentation isolates breaches, enables differentiated security policies, and limits lateral movement.
Covers stateless, stateful, and next-generation firewalls; ACL rule structure and order; firewall placement at segment boundaries and internet ingress/egress points; and writing permit/deny rules.
Covers NIDS, NIPS, and SIEM tools; AI-based threat detection and alert thresholds; signature-based vs. anomaly-based vs. hybrid detection trade-offs; and identifying ARP poisoning, MAC flooding, and evil-twin attacks in log files.
Adversaries exploit network protocols to intercept data, disrupt services, or move laterally across a LAN. ARP poisoning is the core on-path attack: the adversary sends falsified ARP packets to the default gateway, linking the target's IP address to the adversary's MAC address so traffic is rerouted through the adversary's device. MAC flooding overwhelms a switch's MAC address table with fake entries, forcing it to broadcast all traffic. DNS poisoning redirects users to malicious sites by corrupting DNS records. DoS attacks flood a network with traffic to deny service to legitimate users. Vulnerability scanners can assess these risks and produce reports with severity ratings and mitigation recommendations.
| Attack | Mechanism | CIA Impact |
|---|---|---|
| ARP poisoning | Falsified ARP packets redirect traffic to adversary | Confidentiality, Integrity |
| MAC flooding | Overflow switch MAC table to force broadcast | Confidentiality |
| DoS | Flood network to exhaust resources | Availability |
| DNS poisoning | Corrupt DNS records to redirect users | Integrity, Confidentiality |
| MAC spoofing | Fake MAC address to impersonate a device | Confidentiality, Integrity |
Managerial controls are written policies that set minimum configuration standards for network devices. A router security policy bans local user accounts, disables unnecessary services like Telnet, and requires a firewall. A switch security policy requires port security and MAC filtering. A VPN policy defines which roles can use a VPN and what authentication is required. For wireless, organizations disable beacon frame broadcasting to hide the network's SSID, control signal strength so the signal does not extend beyond the physical space, require WPA3 encryption (WEP, WPS, and original WPA are insecure), and enforce MAC filtering and user authentication on wireless access points.
| Wireless Protocol | Security Status |
|---|---|
| WEP | Insecure - known vulnerabilities |
| WPS | Insecure - known vulnerabilities |
| WPA (original) | Insecure - known vulnerabilities |
| WPA2 | Acceptable but aging |
| WPA3 | Currently strongest - recommended |
Network segmentation divides one large network into smaller, isolated zones so that a breach in one segment cannot spread freely to others. A screened subnet (DMZ) sits between the public internet and the internal private network, holding publicly facing resources like web servers while keeping them separated from internal systems. Subnetting uses IP addressing to create distinct subnets, containing breaches to a smaller number of devices. VLANs use switches to logically separate devices that are physically connected to the same hardware. Port security on switches limits the number of MAC addresses per port, preventing MAC flooding. Different segments can have different security policies applied independently.
| Segmentation Method | How It Works | Primary Benefit |
|---|---|---|
| Screened subnet (DMZ) | Firewall zones separate public-facing and internal segments | Isolates public resources from internal network |
| Subnetting | IP addressing creates distinct address ranges | Contains breaches to fewer devices |
| VLAN | Switch-level logical separation | Segments devices on shared physical hardware |
A firewall permits or denies network traffic using a set of rules called an access control list (ACL). Stateless firewalls filter based on packet header information only: IP address, port, and protocol. Stateful firewalls also track the state of active connections, allowing more precise control. Next-generation firewalls (NGFWs) add deep packet inspection, intrusion prevention, and application-layer filtering. ACL rules are checked in order and the first matching rule is applied, so rule order matters. Each network segment and each ingress or egress point between the internal network and the internet should have a firewall. A typical ACL rule specifies direction (inbound or outbound), filter criteria (IP, port, protocol, or application), and action (permit or deny). For example: Allow inbound TCP port 22 from ALL permits SSH traffic; Deny inbound TCP port 80 from 192.168.1.0/24 blocks HTTP from that subnet.
| Firewall Type | Filtering Basis | Additional Capabilities |
|---|---|---|
| Stateless | Packet headers (IP, port, protocol) | None beyond header fields |
| Stateful | Headers plus connection state | Connection-aware rules |
| NGFW | Headers, state, and payload | Deep packet inspection, intrusion prevention, app filtering |
Detection tools analyze log data from switches, routers, firewalls, and user devices to find indicators of compromise (IoCs). A NIDS monitors network traffic and generates alerts when it detects malicious activity. A NIPS does the same but can also respond automatically by closing ports, blocking IP or MAC addresses, or rejecting protocols. A SIEM aggregates and correlates data from multiple sources across the network. AI-based detection algorithms classify traffic patterns as malicious or normal using probabilistic scoring; organizations set their own alert thresholds, balancing missed attacks against alert fatigue. Signature-based detection compares traffic to a database of known IoCs and is fast with low false positives but misses novel attacks. Anomaly-based detection compares traffic to a baseline and catches new attacks but produces more false positives and requires more expensive hardware. Hybrid detection combines both methods at the highest cost. Specific attacks have specific log signatures: ARP poisoning shows duplicate MAC address ARP packets; MAC flooding shows a surge of Ethernet frames with different MACs; evil-twin attacks appear as suspicious SSIDs near legitimate ones.
| Detection Method | Best For | False Positives | Cost |
|---|---|---|---|
| Signature-based | High traffic volume, known attacks | Very low | Lower |
| Anomaly-based | Consistent traffic patterns, novel attacks | Higher | Higher |
| Hybrid | Comprehensive coverage | Moderate to high | Highest |
Try AP-style multiple-choice questions and written prompts after you review the notes.
| Term | Definition |
|---|---|
| firewall | Software or hardware that permits or denies network traffic based on an ordered set of ACL rules; can be standalone or integrated into a router. |
| DMZ | A screened subnet between the public internet and the internal private network that holds publicly facing resources at a lower security level. |
| screened subnet | A network segment created by firewall zones that separates public-facing servers from the internal network; also called a DMZ. |
| network segmentation | Dividing a network into smaller isolated zones so a breach in one segment cannot spread freely to others. |
| VLAN | A logical network segment created on a switch that separates devices without requiring separate physical hardware. |
| subnetting | Using IP addressing to divide a network into distinct subnets, limiting how far a breach can spread. |
| MAC flooding | Sending large numbers of Ethernet frames with different MAC addresses to overflow a switch's MAC table, forcing it to broadcast all traffic. |
| MAC spoofing | Faking a MAC address to impersonate a legitimate device on a network, often used in ARP poisoning or to bypass MAC filtering. |
| DoS attack | A denial-of-service attack that floods a network or device with traffic to exhaust resources and block legitimate users. |
| signature-based detection | Compares network traffic to a database of known IoC signatures; fast with very low false positives but cannot detect novel attacks. |
| anomaly-based detection | Compares traffic to a recorded baseline of normal activity; detects new attacks but produces more false positives and requires more processing resources. |
| indicator of compromise | Evidence in network traffic or log data that suggests malicious activity has occurred or is in progress. |
| port security | A switch setting that limits the number of MAC addresses allowed on a single port, preventing MAC flooding. |
| virtual private network | An encrypted tunnel that allows remote users to access an organization's internal network securely over the public internet. |
| false positive | A detection alert triggered by legitimate traffic that is incorrectly classified as malicious; high rates cause alert fatigue. |
A NIDS only detects and alerts; it does not block traffic. A NIPS can both detect and respond by closing ports or blocking addresses. Students often say NIDS blocks attacks, which is incorrect.
Firewalls apply the first matching ACL rule and stop checking. If a broad permit rule appears before a specific deny rule, the deny rule never executes. Rule order is a core configuration skill in Topic 3.4.
Signature-based detection is faster and has almost no false positives but cannot catch novel attacks. Anomaly-based detection catches new attacks but produces more false positives and costs more. Students frequently reverse these properties.
A screened subnet (DMZ) is a lower-security zone that holds publicly facing resources. It is not part of the internal private network. Placing sensitive internal systems in the DMZ removes the protection segmentation is designed to provide.
MAC filtering can be bypassed through MAC spoofing. It is one layer of wireless defense, not a complete solution. Strong encryption like WPA3 and user authentication are also required.
Expect questions that describe network behavior (for example, a default gateway receiving unexpected ARP packets, or a switch broadcasting all traffic) and ask you to identify the attack type, explain the mechanism, and name the CIA triad component at risk. Being able to trace an attack step by step is more useful than memorizing a definition.
Questions may present a set of ACL rules and ask you to determine whether a specific packet is permitted or denied, or to identify a misconfiguration caused by rule order. You may also be asked to write a rule that meets a stated requirement, such as allowing SSH from all sources or blocking HTTP from a specific subnet.
Questions may describe an organization's network conditions (traffic volume, budget, sensitivity of data, likelihood of novel attacks) and ask you to select and justify a detection method or segmentation approach. Knowing the trade-offs between signature-based and anomaly-based detection, or between a DMZ and a VLAN, lets you reason through these comparisons rather than guess.
Open the individual guides for Unit 3 when you want a closer review of one topic.
browse guidesAP Cyber Unit 3: Securing Networks covers 5 topics: Network Vulnerabilities and Attacks (3.1), Protecting Networks with Managerial Controls and Wireless Security (3.2), Network Segmentation (3.3), Firewalls (3.4), and Detecting Network Attacks (3.5). The unit focuses on how data is protected in transit and how defenders identify and stop network threats. See the full topic breakdown at /ap-cybersecurity/unit-3.
The AP Cyber Unit 3 progress check pulls questions from all 5 topics in Securing Networks: network vulnerabilities and attacks, wireless security, segmentation, firewall configuration, and detecting network attacks using log analysis. The MCQ part tests conceptual knowledge, while the FRQ part asks you to apply defensive strategies to realistic scenarios. For matched practice aligned to these topics, visit /ap-cybersecurity/unit-3.
AP Cyber Unit 3 FRQs typically ask you to analyze a network scenario and recommend defensive measures, such as where to place a firewall, how to segment a network, or how to interpret log files for indicators of compromise (IoCs). Topics 3.3, 3.4, and 3.5 are the most common sources for these scenario-based questions. To practice, write out your reasoning in full sentences, justify each recommendation with a specific concept like segmentation or packet filtering, and check your logic against the topic objectives at /ap-cybersecurity/unit-3.
The best place to find AP Cyber Unit 3 practice questions, including multiple-choice and practice test sets, is /ap-cybersecurity/unit-3. You'll find MCQs covering network vulnerabilities, wireless security, firewalls, and log-based detection, organized by topic so you can target exactly where you need more work.
Start AP Cyber Unit 3 by building a clear picture of how network attacks work (3.1) before moving into defenses. Study each protective layer in order: managerial controls and wireless security (3.2), then segmentation (3.3), then firewalls (3.4). Finish with log analysis and indicators of compromise in 3.5, since detecting attacks ties everything together. A few concrete steps that help: - Draw network diagrams showing where firewalls and segments go. - Practice reading sample log files and flagging suspicious patterns. - For each attack type in 3.1, write one sentence describing the matching defense. - Test yourself with MCQs at /ap-cybersecurity/unit-3 after each topic, not just at the end.