IP Subnetting from Beginning to Mastery

12+ Hours of Video Instruction
Overview
Learn Subnetting, Do Subnetting, Master Subnetting: Big Ideas, Key Calculations, and How to Go Fast

Overview
To build the networks used throughout the world you must understand the single most important networking protocol: Internet Protocol, or IP. IP itself has several components, most notably IP addressing, IP routing, IP routing protocols, and of course, IP subnetting.

Unfortunately, learning IP subnetting can be a big challenge. For example, IP subnetting includes many interwoven ideas. Many common tasks in networking require knowledge of those fundamentals. However, output and figures that describe IP networks do not describe the underlying concepts; they just list the numeric facts about addresses and subnets. Without proper background knowledge, people can struggle to connect the facts to the ideas and make the correct conclusions.

Additionally, subnetting math causes the kinds of challenges to both new learners and long-time IT practitioners. Subnetting math works a lot like math word problems did for us all back in school. Thankfully, all the subnetting math can be understood with a little explanation and practice. However, subnetting includes enough different ideas, terms, and math processes so that you might struggle in choosing what number you need to find, what math process to use, and what the results mean once calculated.

This complete IP Version 4 (IPv4) Subnetting course sets out to solve these problems. The course works through a series of topics about some big ideas, followed by the related subnetting math, and then with available practice for you to build the skill level you need for your purposes. No matter your motivation or current job role, this course helps you:

• Learn subnetting: Understand the ideas and terms in each part of IPv4 subnetting, how to use the ideas in the related mathematical processes, and the purpose and meaning of the facts learned by those processes.
• Do subnetting: Work through a sequence to first learn by seeing the process, and then transition to doing the process through practice problems with video explanations, internalizing the process so you can do it on your own.
• Go faster at subnetting: For those who work with subnetting math every week, or who are studying for certification exams, you need to also practice to the point of going fast at these processes. The course discusses speed goals, how to practice for speed, and how to set reasonable speed expectations.

Whether you just want to finally understand subnetting, want to finally be able to do the math, or need to be ready to breeze through the Cisco CCNA exam, this course can help you master IPv4 subnetting. Be better at understanding the ideas, have better conversations at work, be more effective at troubleshooting, reduce the time pressure on Cisco exams—all those can be achieved with this course.

About the Instructor

Wendell Odom, CCIE 1624 Emeritus, is the leading CCNA author and trainer in the world. He wrote the first-ever Cisco Press certification guide of any kind, with the latest two-volume CCNA set being his eighth edition of CCNA Cert Guide titles. In addition to writing another dozen or so editions of other networking books, Wendell has a long history as an instructor. He taught hands-on networking lab workshops while at IBM and taught hundreds of authorized Cisco course events after becoming one of the first Certified Cisco Systems Instructors. Wendell recently completed a new video course as well as a practice question product about IP Subnetting, published in early 2020. You can catch Wendell online through Twitter (@WendellOdom), but please don’t tweet the scores of the latest Barcelona football match—he probably hasn’t finished watching the DVR recording.

Skill Level
Beginner

Learn How To

• Understand how the subnet ID and subnet mask together represent a subnet
• Identify and describe IPv4 addressing and subnetting processes that can be used to reveal facts about a TCP/IP subnet.
• Understand the concepts, and perform the math, to finding a subnet ID, subnet broadcast address, finding the range of IP addresses in the subnet, beginning with an IP address and mask.
• Understand the meaning and purpose of subnet masks and perform the math to manipulate masks into different formats.
• Describe the details of the IPv4 address space, address classes, and predict facts about a class A, B, or C network.
• Understand the differences between the choices enterprises make when using entire public IP networks, entire private IP networks, and/or smaller public CIDR blocks in their enterprise networks
• Analyze and describe a corporate subnetting plan, using correct terms and math processes, about the number of subnets in the design, the number of host addresses in each subnet, and the possible subnet IDs per the design.
• Describe how a subnet mask controls the specifics of a subnetting design.
• Analyze the mask used in a design to determine the number of subnets created and the number of hosts per subnet.
• Develop a personalized plan for the degree to which you plan to learn each subnetting math process for everyday use and for any upcoming exams.
• Describe what it means to use Variable Length Subnet Masks (VLSM) and how using VLSM impacts various subnetting processes.

Who Should Take This Course

• IT professionals who want to understand subnetting concepts, and understand the math, even if they choose to rely on calculator after class.
• Networking professionals who need to master subnetting concepts, understand all the math, and perform at least some of the math processes on their own without a calculator regularly in their jobs.
• Network certification candidates (Cisco CCNA, CCNP, CompTIA Network+, and so on) who need to be ready to do the math, with no calculator, and no reference information, at speed, at least for exam day.

Course Requirements
Prerequisites:

• No required prerequisites
• Useful suggested reading prior to using the product: You will appreciate the subnetting topics of this class if you know the most basic concepts of IPv4 routing, routers, LANs, and WANs beforehand. You can get that level of knowledge from reading these chapters in the book, “CCNA 200-301 Official Cert Guide, Volume 1”. In particular:
• Chapter 2: “Fundamentals of Ethernet LANs”
• Chapter 3: “Fundamentals of WANs and IP Routing”
• Chapter 8: “Implementing Ethernet Virtual LANs”, using only the section titled “Virtual LAN Concepts”

Materials, downloads, or Supplemental Content needed in advance

• None

Resources

• None

Lesson descriptions

Lesson 1:

This lesson includes several videos with advice to you about how to go about learning IP subnetting and discusses options for more subnetting practice for those of you who want to go fast in answering subnetting questions for exam prep.

Lesson 2:

This lesson discusses the fundamentals of three TCP/IP features related to IP subnetting. These features: IP addressing, IP routing, and IP routing protocols.

Lesson 3:

This lesson defines and identifies the core concepts of what an IP subnet is and what it means to subnet a network.

Lesson 4:

Lesson 4 introduces the ideas and processes related to finding facts about a subnet, namely: the subnet ID, the subnet broadcast address, and the range of addresses usable as host addresses. The lesson shows you the concepts and processes for the limited cases of using mask values of /16 and /24, which are the two easiest cases mathematically.

Lesson 5:

Lesson 5 provides a series of video practice question that use the process detailed in lesson 4 to find the facts about a subnet.

Lesson 6:

Lesson 6 takes the subnetting process introduced in lesson 4 adds the details for the same process when using mathematically difficult masks. The process answers the same questions as lesson 4: given an address and mask, what are the subnet ID, the subnet broadcast address, and the range of addresses usable as host addresses. The lesson focuses on cases in which the mask is neither /16 nor /24.

Lesson 7:

Lesson 7 provides a series of practice question videos that use the process detailed in lesson 6 to find the facts about a subnet, particularly for cases with difficult masks (that is, when the mask is neither /16 nor /24).

Lesson 8:

Lesson 8 begins with two videos about subnet masks: one that explains the core concepts of what a mask is and how it is used, and another that explains the three mask formats. The rest of lesson 8 focuses on two processes:

• To convert from a prefix mask to a binary mask and then finally to a dotted-decimal mask
• Vice-versa.

Lesson 9:

Lesson 9 provides a series of practice question videos that use the process detailed in lesson 8:

• Half about converting from DDN to prefix
• Half about converting prefix to DDN

Lesson 10:

Lesson 10 contains several videos which together tell the story of how enterprises use IPv4 addresses. That story weaves through the idea of public and private IP addresses and shows why many companies use a private class A, B, or C network – which is why most IPv4 subnetting subdivides one or more of these private IP networks.

Lesson 11:

Module 2’s Lessons 5 and 7 show how to find facts about IP subnets. Lesson 11 shows you how to find facts about the Class A, B, and C IP networks. The videos in this lesson focus on the processes to list facts about IP networks and, given an IP address and mask, to find:

• The network ID
• The network broadcast address
• The range of addresses usable as host addresses

Lesson 12:

Lesson 12 provides a series of practice question videos that use the process detailed in lesson 10: In particular, each QA asks you to:

• Lists facts about classful networks, like the class and default mask
• Calculate the network ID and network broadcast address

Lesson 13:

This entire module focuses on interpreting an existing subnetting design – a design that implies a list of subnet IDs. Lesson 13 shows the numeric patterns you can find in the lists of subnet IDs so that you can have more confidence as you work through the details in the processes in the upcoming lessons in this module.

Lesson 14:

Lessons 14 shows how to list all the subnet IDs in an existing design, assuming either of the two simplest cases, including:

• Subnetting a class A network with a /16 mask
• Subnetting a class B network with a /24 mask

Lesson 15:

Lesson 15 provides a series of practice question videos that use the process detailed in lesson 14: In particular, each QA asks you to:

• List the first four and last four subnet IDs in a design

Lesson 16:

Lesson 16 shows how to list all the subnet IDs in an existing design. However, this lesson expands to include more challenging cases compared to lesson 14, namely cases with less than 256 subnets. Those cases happen to use masks other than /16 and /24, a fact that makes the math processes require some extra steps.

Lesson 17:

Lesson 17 provides a series of practice question videos that use the process detailed in lesson 16: In particular, each QA asks you to:

• List the first four and last four subnet IDs in a design

Lesson 18:

Lesson 18 provides details for anyone who wants to cover every case of how to list all subnets. Lesson 18 focuses on cases with more than 256 subnets. Those cases use more difficult masks, and more detailed processes, and as a result, require more work.

Lesson 19:

Lesson 19 provides a series of practice question videos that use the process detailed in lesson 18: In particular, each QA asks you to:

• List the first four and last four subnet IDs in a design

Lesson 20:

Lesson 20 explains logic and processes that make the following assumptions:

• Someone else chose a class A, B, or C network.
• Someone else performed a subnet design and chose one mask to use for all subnets.

Lesson 20 shows how to interpret that design to find:

• The number of hosts per subnet in each subnet.
• The number of subnets in the network.

Lesson 21:

Lesson 21 provides a series of practice question videos that use the process detailed in lesson 20. Each question gives you the design – a class A, B, or C network, along with the one mask used – and you find these values:

• The number of hosts per subnet in each subnet.
• The number of subnets in the network.

Lesson 22:

Lesson 22 places you as the designer of the subnetting plan. In particular, you begin the process with some gathered requirements like these:

• A class A, B, or C network.
• The required number of hosts per subnet the design should create.
• The required number of subnets the design should create.
• A requirement to use one mask value, and one mask value only, for all subnets.

Your job is to decide what single mask value would work. This lesson discusses the process and shows several examples.

Lesson 23:

Lesson 23 provides a series of practice question videos that use the process detailed in lesson 22. Each question gives you the design requirements as follows, and you list the mask value(s) that would meet the requirements:

• A class A, B, or C network.
• The required number of hosts per subnet the design should create.
• The required number of subnets the design should create.
• A requirement to use one mask value, and one mask value only, for all subnets.

Lesson 24:

Lesson 24 defines the concept of variable length subnet masks (VLSM) – a subnet design choice in which the subnets of a single class A, B, or C network use more than one subnet mask. That single statement defines VLSM, but VLSM and its impact can be easily misunderstood. Lesson 24 sets about to explain the facts and then explain the design tradeoffs of the choice of whether to use VLSM or not.

Lesson 25:

The chance of making a mathematical mistake in a subnet design is relatively low when not using VLSM, but more likely when using VLSM. In particular, a design mistake might create two subnets whose address ranges overlap – and with VLSM, it is more difficult to notice that mistake. Lesson 25 defines the issues surrounding this type of design mistake, and then presents an organized process you can use to discover any such overlapping IP subnets.

Lesson 26:

Lesson 26 provides a series of practice question videos that use the process detailed in lesson 25. Each question gives you:

• A set of planned IP addresses/masks.

Your job: discover if any of the subnets implied by the address/mask pairs overlap.

Lesson 27:

When not using VLSM, you can calculate all the subnet IDs in the design beforehand, and that process results in a list of subnets with no overlapping addresses. When using VLSM, you cannot predict and pre-list a list of subnets. Then, each time you need a new subnet, you choose a mask to use, and you need to find a new subnet ID that does not overlap with any existing subnets – a process that can result in mistakes that result in address overlaps.

Lesson 27 defines the issues surrounding this type of design mistake, and then presents an organized process you can use to choose a new subnet ID to use in a design.

Lesson 28:

Lesson 28 provides a series of practice question videos that use the process detailed in lesson 27. Each question gives you:

• A set of existing (deployed) IP subnets.
• The mask for a presumptive new subnet ID.

Your job: Find the numerically lowest new subnet ID you could add to the design without overlapping with any of the existing subnets.

Lesson 29:

If your goal is to pass the CCNA exam, you should watch and consider the advice in all the videos in this lesson. This lesson focuses on the difference between learning subnetting for your every-day job in networking vs. being ready to pass the exam.

In particular, this lesson walks you through how to be ready for subnetting questions in the exam. That includes a discussion of the exam and the fact that you may want to plan to use some tables and tools on the exam. It also includes a suggestion for an honest self-assessment of your skills (% correct) and speed, both of which are important for the exam. The lesson closes with some suggestions for where to get more practice – and anyone wanting to do well on the CCNA exam can always use more subnetting practice.

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