N10-009 CompTIA Network+ Certification Exam Free Practice Exam Questions (2026 Updated)

802.1Q tagging, also known as VLAN tagging, is used to identify VLANs on a trunk link between switches. This allows the switches to transfer data for multiple VLANs (or networks) over a single physical connection. This method ensures that traffic from different VLANs is properly separated and managed across the network.References: CompTIA Network+ study materials.

Role of the Hosts File:

The hosts file is a local file on a computer that maps hostnames to IP addresses. It can be used to override DNS resolution by providing a static mapping of a hostname to an IP address.

Common Issues with the Hosts File:

If an incorrect IP address is mapped to a hostname in the hosts file, it can cause the computer to resolve the hostname to the wrong IP address. This can lead to navigation issues for specific websites while other users, relying on DNS, do not face the same problem.

Why Other Options are Less Likely:

Self-signed certificate: Relates to SSL/TLS and would cause a security warning, not a navigation failure.

Nameserver record: Affects all users, not just one.

IP helper: Used to forward DHCP requests and is unrelated to DNS resolution issues.

Troubleshooting Steps:

Check the hosts file on the affected user's computer (C:\Windows\System32\drivers\etc\hosts on Windows or /etc/hosts on Unix/Linux).

Look for entries that map the problematic hostname to an incorrect IP address and correct or remove them.

The correct answer is VLSM (Variable Length Subnet Masking). According to the CompTIA Network+ N10-009 objectives, VLSM allows a network administrator to create subnets of different sizes within the same network, making it ideal for environments where subnet host requirements vary.

In this scenario, the technician must support multiple subnet sizes—60 hosts, 15 hosts, and seven hosts—within a single Class C network. Using a single subnet mask for all eight subnets would either waste a large number of IP addresses or fail to meet host requirements. VLSM solves this problem by allowing each subnet to be assigned a custom subnet mask that closely matches its host needs, maximizing address efficiency.

CIDR enables classless addressing and route aggregation but does not, by itself, describe creating multiple subnet sizes within a single address block. APIPA is a self-assigned addressing mechanism used when DHCP fails and has no relevance to subnet design. RFC 1918 defines private IP address ranges but does not address subnetting strategies.

The Network+ objectives emphasize VLSM as a best practice for efficient IP address management, especially in enterprise environments where conserving address space and meeting diverse departmental requirements are critical. In this case, VLSM is the only solution capable of meeting all stated constraints.

OSPF (Open Shortest Path First) is a link-state routing protocol that uses the Dijkstra algorithm, also known as the shortest path first (SPF) algorithm, to determine the most efficient routes.

From Andrew Ramdayal’s guide:

“OSPF is a link-state routing protocol that provides fast, efficient path selection using the shortest path first (SPF) algorithm.”

If a workstation can access the internet and printers (likely in another VLAN) but not internal servers, the port was likely placed into the wrong VLAN after the move. VLAN assignment controls Layer 2 segmentation, restricting access to resources on different VLANs.

A. A wrong default gateway would prevent internet access.

C. An error-disabled port would block all connectivity.

D. A duplicate IP would cause general network issues, not just missing server access.

References (CompTIA Network+ N10-009):

Domain: Network Troubleshooting — VLAN misconfiguration, connectivity issues.

The correct metric is RTO (Recovery Time Objective). RTO defines the maximum acceptable time to restore services after a disruption, ensuring business continuity. For example, if the RTO is 4 hours, systems must be back online within that timeframe after an outage.

B. MTBF (Mean Time Between Failures) measures reliability by calculating the average time between hardware failures.

C. RPO (Recovery Point Objective) defines how much data loss (in terms of time, such as last backup point) is acceptable.

D. MTTR (Mean Time to Repair) measures the average time taken to fix a failure but is not a predefined business requirement like RTO.

Organizations define RTOs during disaster recovery planning to align IT recovery capabilities with business needs.

References (CompTIA Network+ N10-009):

Domain: Networking Concepts — Business continuity metrics (RTO, RPO, MTBF, MTTR).

Introduction to Subinterfaces:

Subinterfaces are logical interfaces created on a single physical interface. They are used to enable a router to support multiple networks on a single physical interface.

Use Case for Subinterfaces:

Subinterfaces are commonly used in scenarios where VLANs are implemented. A router with a single physical LAN port can be configured with multiple subinterfaces, each associated with a different VLAN.

This setup allows the router to route traffic between different VLANs.

Example Configuration:

Consider a router with a single physical interface GigabitEthernet0/0 and two VLANs, 10 and 20.

interface GigabitEthernet0/0.10

encapsulation dot1Q 10

ip address 192.168.10.1 255.255.255.0

!

interface GigabitEthernet0/0.20

encapsulation dot1Q 20

ip address 192.168.20.1 255.255.255.0

The encapsulation dot1Q command specifies the VLAN ID.

Explanation of the Options:

A. A router with only one available LAN port: This is correct. Subinterfaces allow a single physical interface to manage multiple networks, making it essential for routers with limited physical interfaces.

B. A firewall performing deep packet inspection: Firewalls can use subinterfaces, but it is not a requirement for deep packet inspection.

C. A hub utilizing jumbo frames: Hubs do not use subinterfaces as they operate at Layer 1 and do not manage IP addressing.

D. A switch using Spanning Tree Protocol: STP is a protocol for preventing loops in a network and does not require subinterfaces.

Conclusion:

Subinterfaces provide a practical solution for routing between multiple VLANs on a router with limited physical interfaces. They allow network administrators to optimize the use of available hardware resources efficiently.

Security groups in cloud environments act as virtual firewalls for VM instances, controlling inbound and outbound traffic based on specified rules.

From Andrew Ramdayal’s guide:

“Network security groups are used to control inbound and outbound traffic to cloud resources within a VPC. They act as a virtual firewall for associated instances...”

Troubleshooting poor performance of a newly installed access point involves multiple steps. Checking for network bottlenecks and ensuring the device firmware is up to date are crucial first steps. The document confirms:“Network bottlenecks can severely limit the performance of even the fastest wireless access points, so it’s essential to verify that no other devices are causing a slowdown. In addition, keeping firmware updated ensures optimal performance and security.”

A full-tunnel VPN forces a remote user’s traffic—including access to public internet resources—to traverse the corporate VPN tunnel and egress from the organization’s network. This is commonly required to ensure consistent enforcement of corporate security controls such as web filtering, IDS/IPS inspection, DLP policies, logging, and access control. In Network+ terms, full-tunnel VPNing routes the user’s default gateway through the VPN, meaning both internal traffic (to corporate subnets) and external traffic (to internet destinations) is sent through the encrypted tunnel.

By contrast, a split-tunnel VPN (not listed) would send only corporate-bound traffic through the VPN while allowing internet traffic to go directly out the user’s local ISP—reducing corporate bandwidth usage but also reducing centralized inspection and control. Clientless VPN usually refers to browser-based access to specific internal applications without a full network tunnel for all traffic. Site-to-site VPN connects entire networks to each other (e.g., branch office to HQ) rather than an individual remote user. SSE (Security Service Edge) is a cloud security framework/service model, not the classic VPN configuration described in the question. Hence, full-tunnel is the correct answer.

TCP port 443 is reserved for HTTPS (Hypertext Transfer Protocol Secure), which uses TLS encryption to secure web traffic. It is the standard port for encrypted web communications.

A. Telnet uses TCP port 23.

B. SMTP commonly uses TCP ports 25, 465, or 587.

D. SNMP typically uses UDP ports 161 (queries) and 162 (traps).

References (CompTIA Network+ N10-009):

Domain: Network Standards, Protocols, and Implementations — Common ports and services.

Understanding 2.4GHz Interference:

The 2.4GHz frequency range is commonly used by many devices, including Wi-Fi, Bluetooth, and various industrial equipment. This can lead to interference and degraded performance.

Mitigation Strategies:

5GHz Frequency:

The 5GHz frequency band offers more channels and less interference compared to the 2.4GHz band. Devices operating on 5GHz are less likely to encounter interference from other devices, including industrial equipment.

Non-overlapping Channels:

In the 2.4GHz band, using non-overlapping channels (such as channels 1, 6, and 11) can help reduce interference. Non-overlapping channels do not interfere with each other, providing clearer communication paths for Wi-Fi signals.

Why Other Options are Less Effective:

Mesh Network: While useful for extending network coverage, a mesh network does not inherently address interference issues.

Omnidirectional Antenna: This type of antenna broadcasts signals in all directions but does not mitigate interference.

Captive Portal: A web page that users must view and interact with before accessing a network, unrelated to frequency interference.

Ad Hoc Network: A decentralized wireless network that does not address interference issues directly.

Implementation:

Switch Wi-Fi devices to the 5GHz band if supported by the network infrastructure and client devices.

Configure Wi-Fi access points to use non-overlapping channels within the 2.4GHz band to minimize interference.

The correct answer is /25, which is the appropriate subnet mask for dividing an existing Class C network into two equal subnets. According to the CompTIA Network+ N10-009 objectives, subnetting is a core networking concept used to improve network segmentation, performance, and security.

A Class C network uses a default subnet mask of /24 (255.255.255.0), which provides 256 total addresses (254 usable). To split this network into two sections, the administrator must borrow one host bit from the last octet. Borrowing one bit results in a /25 subnet mask (255.255.255.128). This creates two subnets, each with 128 total addresses (126 usable)—an ideal solution for separating two departments such as finance and marketing.

A /24 would not create any segmentation, as it represents the original single network. A /26 would create four subnets, and a /27 would create eight subnets, both of which exceed the requirement of only two sections and unnecessarily reduce the number of available host addresses per subnet.

The Network+ objectives emphasize selecting subnet masks based on organizational requirements, balancing the number of subnets with sufficient host capacity. In this scenario, /25 is the most efficient and correct choice.

In data centers, hot aisle/cold aisle configurations are used to manage airflow and cooling efficiency. Port-side exhausts should be oriented towards the warm aisle to expel hot air and maintain optimal cooling. The document clarifies:

“Equipment with port-side exhausts should be oriented towards the warm aisle to ensure that hot air is properly directed away from the cold air intake areas. This alignment supports effective cooling in data center environments.”

An on-path attack (formerly known as a man-in-the-middle (MITM) attack) involves intercepting and potentially altering communications between two parties without their knowledge. This can be done via techniques like ARP poisoning, rogue access points, or SSL stripping.

Breakdown of Options:

A. Self-signed certificate – These are untrusted SSL certificates but do not intercept traffic.

B. VLAN hopping – VLAN hopping exploits VLAN misconfigurations but does not necessarily intercept communications.

C. On-path attack – Correct answer. This intercepts and modifies traffic between two endpoints.

D. Phishing – Phishing tricks users into revealing credentials rather than intercepting network traffic.

Understanding TTL (Time to Live):

TTL is a value in a DNS record that tells how long that record should be cached by DNS servers and clients. A higher TTL value means that the record will be cached longer, reducing the load on the DNS server but delaying the propagation of changes.

Impact of TTL on DNS Changes:

When an MX record change is made, it may take time for the change to propagate across all DNS servers due to the TTL setting. If the TTL is high, old DNS information might still be cached, leading to email being directed to the old server.

Best Practice Before Making DNS Changes:

To ensure that changes to DNS records propagate quickly, it is recommended to reduce the TTL value to a lower value (such as 300 seconds or 5 minutes) well in advance of making the changes. This ensures that any cached records will expire quickly, and the new records will be used sooner.

Verification of DNS Changes:

After reducing the TTL and making the change to the MX record, it is important to verify the propagation using tools like dig or nslookup.

Comparison with Other Options:

Change the email client configuration to match the MX record: Email clients generally do not need to match the MX record directly; they usually connect to a specific mail server specified in their settings.

Perform a DNS zone transfer prior to the MX record change: DNS zone transfers are used to replicate DNS records between DNS servers, but they are not related to the propagation of individual record changes.

Update the NS record to reflect the IP address change: NS records specify the DNS servers for a domain and are not related to MX record changes.

Introduction to OSI Model:

The OSI model is a conceptual framework used to understand network interactions in seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

Application Layer:

The application layer (Layer 7) is the topmost layer in the OSI model. It provides network services directly to end-user applications. This layer facilitates communication between software applications and lower layers of the network protocol stack.

Reliance on Other Layers:

The application layer relies on the transport layer (Layer 4) for data transfer across the network. The transport layer ensures reliable data delivery through protocols like TCP and UDP.

The network layer (Layer 3) is responsible for routing packets to their destination.

The data link layer (Layer 2) handles node-to-node data transfer and error detection.

The physical layer (Layer 1) deals with the physical connection between devices.

Explanation of the Options:

A. It relies upon other layers for packet delivery: This is correct. The application layer depends on the lower layers (transport, network, data link, and physical) for the actual delivery of data packets.

B. It checks independently for packet loss: This is incorrect. Packet loss detection is typically handled by the transport layer (e.g., TCP).

C. It encrypts data in transit: This is incorrect. Encryption is typically handled by the presentation layer or at the transport layer (e.g., TLS/SSL).

D. It performs address translation: This is incorrect. Address translation is performed by the network layer (e.g., NAT).

Conclusion:

The application layer’s primary role is to interface with the end-user applications and ensure that data is correctly presented to the user. It relies on the underlying layers to manage the actual data transport and delivery processes.

The troubleshooting methodology requires following a logical sequence. In this case, the engineer has already identified the problem (firewall blocking traffic) and confirmed it with evidence (packet captures). The next appropriate step is to create a plan of action that outlines how to resolve the issue and considers potential effects.

A. Implementing the solution is premature without planning.

C. Establishing a theory was already completed during problem isolation.

D. Documentation occurs after resolution.

By carefully planning, the engineer ensures that corrective action won’t cause additional outages or security issues, especially given the scale of the incident (3,000 users).

References (CompTIA Network+ N10-009):

Domain: Network Troubleshooting — Troubleshooting methodology, plan of action.