Technology & IT

Basic Networking Quiz: Test Your Network Fundamentals Knowledge

25 Questions 13 min
Networking skills rank among the most in-demand IT competencies. CompTIA reports that over 350,000 Network+ certifications have been awarded worldwide, and the U.S. Bureau of Labor Statistics projects 6% growth for network-related roles through 2032. This quiz covers the OSI model, TCP/IP, subnetting, DNS/DHCP, common ports, VLANs, firewalls, and wireless fundamentals to help you benchmark your readiness for certification exams and real-world troubleshooting.
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Computer networking - ethernet cable connected to router
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1What is the primary purpose of a network firewall?
2Wi-Fi networks based on IEEE 802.11 standards can operate on both the 2.4 GHz and 5 GHz frequency bands.

True / False

3Select all devices that operate at Layer 2 (Data Link) of the OSI model.

Select all that apply

4What is the key difference between a hub and a switch?
5What command can you use on Windows to release and renew a DHCP-assigned IP address?
6A stateful firewall does not track the state of network connections and allows return traffic that matches an established session.

True / False

7A DNS A record maps a domain name to an IPv4 address.

True / False

8Select all addresses that fall within the 10.0.0.0/8 private address space.

Select all that apply

9Select all items that are common components of a defense-in-depth network security strategy.

Select all that apply

10Select all wireless security protocols that are considered deprecated or insecure.

Select all that apply

11At which OSI layer does a Layer 3 switch make forwarding decisions?
12Flow control and error recovery to ensure reliable end-to-end data delivery are functions of which OSI layer?
13A network uses the subnet mask 255.255.255.192 (/26). How many usable host addresses does each subnet provide?
14Which IP address range is reserved for loopback testing?
15What is the purpose of a default gateway in IP networking?
16A user can ping 8.8.8.8 but cannot reach www.google.com by name. What is the most likely issue?
17What is the purpose of a VLAN (Virtual Local Area Network)?
18What protocol is commonly used to carry multiple VLAN traffic over a single switch-to-switch link?
19What does the TTL (Time to Live) field in an IP packet header prevent?
20What is the primary advantage of the 5 GHz band over 2.4 GHz for Wi-Fi?
21The traceroute (tracert on Windows) utility does not use incrementing TTL values to map the path packets take to a destination.

True / False

22A network engineer notices that frames are arriving with CRC errors. At which OSI layer should the engineer focus troubleshooting?
23A DNS server receives a query it cannot resolve from its own zone files. In a recursive query, what does the server do?
24A TCP sender has a window size of 64 KB and the RTT to the receiver is 100 ms. What is the approximate maximum throughput?
25A next-generation firewall (NGFW) can inspect encrypted HTTPS traffic by performing SSL/TLS decryption inline.

True / False

Common Networking Mistakes That Trip Up Certification Candidates

1) Confusing OSI layers with TCP/IP layers

The OSI model has 7 layers while TCP/IP has 4 (or 5). Many learners mix up which protocols belong to which model. Fix this by memorizing that OSI is a reference model (Physical through Application), while TCP/IP combines several OSI layers into broader categories.

2) Forgetting to subtract network and broadcast addresses from host counts

When calculating usable hosts in a subnet, the formula is 2^n - 2 (not 2^n). The network address (all host bits 0) and broadcast address (all host bits 1) are reserved. Skipping this subtraction is one of the most common subnetting errors.

3) Mixing up TCP and UDP use cases

Students often assume all important traffic uses TCP. In reality, DNS queries, DHCP, TFTP, and real-time protocols like VoIP primarily use UDP for speed. Understand that UDP sacrifices reliability for lower latency, which is intentional for time-sensitive applications.

4) Treating VLANs as a security boundary without routing controls

VLANs segment broadcast domains but do not prevent inter-VLAN traffic by themselves. Without proper ACLs or firewall rules on the Layer 3 device routing between VLANs, traffic can still cross segments. Always pair VLAN segmentation with access control policies.

5) Assuming a firewall blocks everything by default

Firewall behavior depends on its default policy. Some allow all traffic unless explicitly denied. Best practice is an implicit deny (block all) default with explicit allow rules. Always verify the default policy before adding rules.

Network Troubleshooting Scenario Drills: OSI Model, Subnetting, and Security

Work through each scenario and decide: what layer is the issue at, what tool would you use, and what is your fix?

  1. No internet, APIPA address: A user reports no internet access. You run ipconfig and see a 169.254.x.x address. What does this tell you about the DHCP process, and what are your first two troubleshooting steps?
  2. Ping works, browsing fails: A workstation can ping 8.8.8.8 but cannot reach any website by name. At which OSI layer is the failure, and which tool confirms your theory?
  3. New VLAN, no cross-VLAN communication: You created VLAN 20 and assigned ports, but VLAN 20 devices cannot reach VLAN 10. What Layer 3 configuration is missing, and what device provides it?
  4. Slow Wi-Fi in a conference room: Users report slow Wi-Fi during large meetings. A site survey shows your AP is on channel 3 at 2.4 GHz. What is the issue, and which three channels should you consider?
  5. SSH blocked by firewall: A remote admin cannot SSH into a server at 10.0.0.5. The firewall log shows a deny rule matching TCP port 22 to that host. What is the minimum rule change needed, and where in the ACL should it be placed?
  6. Spanning Tree port blocked: A new uplink between two switches is not passing traffic. Show commands reveal the port is in STP blocking state. Why is this happening, and what are two safe ways to resolve it?
  7. Subnet sizing decision: A department needs 50 host addresses on its own subnet. You have the 10.1.0.0/16 space. What is the smallest subnet mask that fits, and how many addresses does it waste?

Authoritative Networking and Cybersecurity References for Further Study

Networking Fundamentals FAQ: OSI Model, Certifications, and Career Paths

Do I need to memorize all seven OSI layers for the CompTIA Network+ exam?

Yes. The OSI model is foundational to the Network+ exam objectives (N10-009). You need to know each layer's name, number, function, PDU (bits, frames, packets, segments), and which protocols and devices operate at each layer. Use the mnemonic Please Do Not Throw Sausage Pizza Away to lock in the order from Layer 1 to Layer 7.

What is the difference between the OSI model and the TCP/IP model?

The OSI model has 7 layers and is a reference/teaching framework. The TCP/IP model has 4 layers (Network Access, Internet, Transport, Application) and maps more closely to how real protocols work. In practice, the OSI model is used for troubleshooting methodology (identify the layer of the problem), while TCP/IP describes the actual protocol stack. For more detail, see CompTIA's Network+ exam objectives.

Which networking certification should I start with?

For most beginners, CompTIA Network+ is the recommended starting point because it is vendor-neutral and covers fundamentals across all networking platforms. If you already have Network+ or equivalent experience, Cisco CCNA is a strong next step for hands-on routing and switching skills. See Cisco's certification page for details.

How long does it take to prepare for the Network+ exam?

Most candidates report 8 to 12 weeks of dedicated study (1-2 hours daily). Key prep areas include: OSI/TCP/IP models, IP addressing and subnetting (practice binary math until it is automatic), common ports and protocols, network devices and their OSI layers, basic security concepts, and hands-on troubleshooting with tools like ping, tracert, nslookup, and netstat.

Are subnetting calculations really used in day-to-day network administration?

Yes. While subnet calculators exist, understanding subnetting is critical for designing networks, reading firewall rules, troubleshooting routing issues, and passing certification exams. Admins regularly need to determine network/broadcast addresses, usable host ranges, and appropriate subnet sizes for new deployments.