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A+ Domain: Networking Fundamentals

IT & Cyber Certifications

A+ Domain: Networking Fundamentals

2 min readPublished 22 Jul 2026

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Networking connects everything you support. A+ expects you to understand IP addressing, common ports and protocols, and how devices communicate across a network.

Beginner: the basics

  • IPv4 addresses (e.g. 192.168.1.10) and the idea of private vs public ranges.
  • DHCP hands out IP addresses automatically; DNS resolves names to IPs.
  • Default gateway — the router that connects your subnet to other networks.
  • Cable types: Cat5e/Cat6 twisted pair, fibre, and RJ45 connectors.

Intermediate concepts

  • Common ports: 80/443 (HTTP/HTTPS), 22 (SSH), 3389 (RDP), 53 (DNS), 25/587 (SMTP).
  • TCP (reliable) vs UDP (fast, connectionless).
  • Wi-Fi standards 802.11 a/b/g/n/ac/ax and 2.4 GHz vs 5 GHz.
  • The OSI model's seven layers as a troubleshooting map.

Advanced considerations

  • Subnet masks and how they define network vs host portions.
  • NAT and why private addresses can share one public IP.
  • VLANs to segment traffic logically.

Practical examples

  • Using ipconfig/ifconfig, ping, tracert and nslookup to diagnose connectivity.
  • Configuring a home/office router: SSID, WPA2/WPA3, DHCP scope.

Common mistakes

  • Confusing DNS and DHCP roles.
  • Assuming a device with an APIPA (169.254.x.x) address has a working connection.
  • Forgetting that a firewall or wrong subnet mask can block traffic that 'should' work.

Best practices

  • Work up the OSI layers when troubleshooting — start at the physical layer.
  • Document IP schemes and label cables.
  • Use WPA2/WPA3 and change default router credentials.

What employers expect

You can explain how a packet gets from a PC to a website, read basic network settings, and use command-line tools to isolate where a connection fails.

Technical interview questions

  1. What is the difference between DHCP and DNS?
  2. Name the ports for HTTP, HTTPS, SSH and RDP.
  3. What does a default gateway do?
  4. How would you troubleshoot 'the internet is down' for one user?

Behavioural interview questions

  1. Tell me about a time you fixed a connectivity problem.
  2. Describe explaining a network issue to a non-technical colleague.

Practice questions

  1. Which port does HTTPS use? (443)
  2. Which service resolves domain names to IPs? (DNS)
  3. A 169.254.x.x address means what failed? (DHCP)

Where this fits in your A+ pathway

This is one part of the CompTIA A+ study hub. When you're confident here, review PC Hardware and move on to Mobile Devices.

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Interview Intelligence

How this topic actually shows up in interviews — and how to demonstrate you understand it.

Why employers ask about this

Networking basics separate a capable support tech from a button-pusher; interviewers check you understand IPs, DNS and DHCP.

Technical questions
What is an IP address and a subnet mask?+

An IP identifies a device on a network; the subnet mask marks which part is the network and which is the host.

What's the difference between a switch and a router?+

A switch connects devices within a network (Layer 2, MAC); a router connects different networks (Layer 3, IP).

Behavioural questions
Describe explaining a network issue to a colleague.+

Keep it simple and structured, focusing on impact and next steps.

Real-world scenarios
“A user has a 169.254.x.x address and no internet.”+

Expected answer: Recognise APIPA — DHCP failed; check the DHCP server/cabling and renew the lease.

Common candidate mistakes
  • •Confusing a switch with a router.
  • •Not recognising an APIPA address as a DHCP failure.
Practise in AI Interview™Rehearse these questions, scored.Plan with Career Coach™A personalised path to your goal.Evidence it in Career Passport™Prove this skill to employers.

Employability Intelligence

Where this knowledge takes you — the jobs, skills and certifications it feeds into.

Relevant roles
IT Support TechnicianNetwork SupportHelp Desk Analyst
Skills you're proving
IP addressingDNS & DHCPCablingBasic troubleshooting
Recommended certifications
CompTIA Network+Networking Fundamentals
Career progression

IT Support → Network Support → Network Administrator (via Network+).

What employers expect

That you understand core networking well enough to troubleshoot connectivity.

Frequently asked questions

Do I need to master subnetting for A+?

A+ requires only a working understanding of IP addressing and subnet masks — deep subnetting maths is more of a Network+ topic. Focus on recognising private ranges, gateways and basic masks.

What is the OSI model and why does it matter?

The OSI model breaks networking into seven layers, from physical cabling up to applications. It gives you a structured troubleshooting map — you work up the layers to find where communication breaks down.

Should I learn ports by heart?

Yes. Knowing common port numbers (80, 443, 22, 3389, 53) on sight is expected in both the exam and real support work, and it speeds up firewall and connectivity troubleshooting.

Related guides

CompTIA A+ (220-1101 & 220-1102): Complete Free Study Guide & Career PathA+ Domain: PC HardwareA+ Domain: Mobile DevicesA+ Domain: Operating Systems

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