WGU D315: Network and Security - Foundations

Where D315 Fits in Your Degree

D315: Network and Security - Foundations is the course where a lot of WGU technology students meet networking for the first time in a serious way. It sits early in cybersecurity, IT, network engineering, and computer science program plans, and it does double duty: it teaches you how data actually moves between machines, and it teaches you the vocabulary and mental models of information security that nearly every later course assumes you already own. WGU documentation lists it as a three-unit course, and it is assessed by a single proctored objective assessment.

Direct answer: Pass D315 by learning the OSI and TCP/IP models cold, drilling IP addressing and subnetting until the math is automatic, and learning protocols alongside their ports and their purpose. Take the pre-assessment early, treat every miss as a study assignment, and re-test until your coaching report is clean.

If you are coming from outside IT, D315 can feel like a language course. There is a genuinely large amount of terminology — protocol names, acronyms, layer numbers, port numbers, device types, attack names — and the assessment expects you to recognize all of it quickly. If you arrive with CompTIA Network+ or Security+ experience, much of the material will feel familiar, and your job is mostly to map what you already know onto WGU's framing. WGU also publishes transfer guidance indicating that several industry certifications, including Network+, Security+, and Cisco's CCNA, may satisfy this requirement outright, so it is worth asking your program mentor before you study anything at all.

This course matters beyond the credit because it is load-bearing. Courses like D325 Networks, D430 Fundamentals of Information Security, and later architecture work such as D488 Cybersecurity Architecture and Engineering build directly on the foundation you lay here. Students who rush D315 often pay for it two terms later.

What the Objective Assessment Actually Covers

The course is organized around identifying network systems and concepts, applying security concepts to networks, and identifying appropriate security solutions. In practice, the assessment draws from these areas:

• Network models — the layers of the OSI model and the TCP/IP model, what happens at each layer, and which devices and protocols belong where.
• Protocols and their purposes — TCP versus UDP, IP, ICMP, ARP, DHCP, DNS, HTTP and HTTPS, FTP and SFTP, SSH, Telnet, SMTP, POP3, IMAP, and SSL/TLS, along with the well-known ports associated with them.
• IP addressing and subnetting — IPv4 structure, address classes, private versus public ranges, subnet masks, CIDR notation, NAT, and an introduction to IPv6.
• Network hardware and topologies — switches, routers, hubs, access points, and firewalls; star, mesh, bus, and ring layouts; LAN, WAN, and wireless networking basics.
• Cloud and virtualization — IaaS, PaaS, and SaaS; public, private, hybrid, and community deployment models; hypervisor types and what virtualization buys you.
• Core security principles — the CIA triad, the AAA framework, least privilege, multifactor authentication, and access control models.
• Security controls and threats — firewalls, intrusion detection and prevention systems, VPNs, encryption fundamentals including symmetric versus asymmetric approaches and hashing, plus common attack categories such as denial of service, man-in-the-middle, spoofing, and social engineering.
• Diagnostic tools — what ping, traceroute, ipconfig or ifconfig, netstat, nslookup, and similar commands tell you, and when you would reach for each.

How Hard Is It, and How Long Should You Budget?

Many students describe D315 as moderate: not conceptually deep, but wide. The difficulty is volume and recall speed rather than reasoning. Students with prior networking exposure or a Network+ background frequently report finishing in a week or two, while students entering from a non-technical background more often describe three to five weeks of steady evening study. Neither range is a promise — your pace depends on how much of the vocabulary is already familiar.

Two things reliably stretch the timeline. The first is subnetting, which stops being hard the moment you have done thirty problems by hand and stays hard indefinitely if you keep watching videos about it instead. The second is the sheer number of acronyms, which rewards spaced repetition and punishes cramming. Plan for short daily sessions rather than weekend marathons.

A Study Routine That Works for This Material

The pre-assessment is your syllabus. Take it in your first few days, before you feel ready, and read the coaching report as a to-do list rather than a grade. It tells you exactly which competency areas need your time, and most students find that two or three areas account for nearly all their misses.

Then structure your study around retrieval, not rereading:

• Build your own recall deck. Make cards for protocol-to-port, protocol-to-purpose, and layer-to-function. Writing the cards is half the learning; a deck someone else made will not stick the same way. Review daily in short bursts.
• Draw the OSI stack from memory every morning. Blank sheet, seven layers, then annotate each with a device, a protocol, and a data unit. When you can do that in ninety seconds without hesitation, a large slice of the assessment becomes straightforward.
• Do subnetting with a pencil. Work problems by hand until you can convert between CIDR and dotted-decimal masks and find the network address, broadcast address, and usable host count without a calculator. Use an online calculator to check your work, never to do it for you.
• Explain security concepts out loud. Say what confidentiality, integrity, and availability each protect against, and give a real control for each. If you can teach it to a family member, you know it.
• Interleave, do not block. Mix networking and security questions in the same session. The assessment does not sort topics neatly, so your practice should not either.
• Retest the pre-assessment. After a focused study block, take it again. Repeat until the report is clean across the board, then schedule the OA while the material is fresh.

Hands-on practice helps the abstractions land. Building a tiny network in a free simulator and watching traffic traverse the layers turns the OSI model from a list into a picture. If you enjoy that side of things, a course like D281 Linux Foundations pairs naturally with the command-line diagnostics covered here.

Where Students Trip Up

• Recognizing terms instead of knowing them. Reading a glossary produces a feeling of familiarity that collapses under a scenario question. Force yourself to produce definitions from a blank page.
• Skipping subnetting because it looks like math. It is arithmetic with a pattern, and it is one of the most reliably testable skills in the course. Avoiding it costs more points than any other single choice.
• Confusing similar protocols. FTP versus SFTP versus TFTP, SSH versus Telnet, POP3 versus IMAP, TCP versus UDP. Study these in contrasting pairs, with the distinguishing feature written on the card.
• Memorizing layer numbers without functions. Knowing that the transport layer is layer four is not enough; you need to know what breaks if it fails and which protocols live there.
• Treating security as separate from networking. Many questions ask you to choose a security solution for a network situation. The two halves of the course are meant to be used together.
• Waiting to schedule the exam. Momentum matters with volume-heavy material. Book the OA as soon as your pre-assessment is solid, not weeks later.

D315 Readiness Checklist

• Can you write out all seven OSI layers in order, with a device and a protocol for each, from memory?
• Can you explain the practical difference between TCP and UDP and name a common use for each?
• Can you match at least fifteen common protocols to their default ports without hesitation?
• Can you take an IP address and CIDR prefix and produce the network address, broadcast address, and usable host range by hand?
• Can you describe what NAT does and why private address ranges exist?
• Can you define the CIA triad and give a concrete control that protects each element?
• Can you distinguish symmetric encryption, asymmetric encryption, and hashing by purpose rather than by definition?
• Can you explain what a firewall, an IDS, an IPS, and a VPN each do, and when you would deploy each one?
• Have you retaken the pre-assessment after studying and cleared the areas your coaching report flagged?

D315 FAQ

Is D315 an objective assessment or a performance assessment?

It is assessed by a single proctored objective assessment. There is no paper or project component, so all of your preparation should point toward recall and scenario questions.

Is D315 the same course as C172?

C172 was the older code for WGU's foundational networking and security course. D315 is the current version students are enrolled in, and program plans and transfer guidance now use the D315 code.

How many competency units is D315 worth?

WGU documentation lists it as a three-unit course. Your own program plan is the authoritative source, since unit counts occasionally differ across degree versions.

Can a certification I already hold clear this course?

WGU's transfer guidance indicates that several networking and security certifications, including CompTIA Network+ and Security+ and Cisco's CCNA, may satisfy this requirement. Confirm with your program mentor or on the official WGU site before you begin studying, because rules vary by program and catalog year.

How much subnetting do I really need?

Enough to work standard IPv4 problems confidently by hand. You do not need advanced routing design, but you should be able to interpret a subnet mask, use CIDR notation, and identify the network and host portions of an address without a tool.

What should I study first if I have almost no networking background?

Start with the OSI model and the vocabulary that hangs off it, then move to IP addressing, then to protocols and ports, and only then to the security half of the course. Building the map before adding details keeps the terminology from feeling arbitrary.

When you are ready to look ahead, browse the rest of the School of Technology guides or the full library of WGU course guides. This site is an independent study resource and is not affiliated with or endorsed by Western Governors University.