# Mask Design Drill 2

Here’s another mask design drill, with the same idea as the previous two posts (chronologically speaking). For those of you with my ICND1 book, Chapter 16 spells out the details, and you can just use this as more practice. The first part of today’s post repeats the general instructions for the drill. It then shows some space, to avoid spoiling the problems. At the bottom, you’ll find three mask design problem statements, so before scrolling down you can start your timer and see how long it takes you to find the answers. Click the poll to let me know how long you took, on average, for each mask design drill!

## Shortcut

Already done these drills? Know what to do? Start your timer, and scroll to the bottom. Otherwise, read on!

## What’s in a Mask Design Drill

Every problem in a mask design drill post gives requirements for you to pick one mask, and one mask only, for all subnets of a class A, B, or C network. Each problem lists these basic facts:

1)     The class (A, B, or C)

2)    The maximum number of host addresses required in the largest subnet

3)    The maximum number of subnets required in the design

4)    If multiple masks meet the requirements, whether the mask should maximize the number of hosts per subnet, or maximize the number of subnets

On that last point, in some cases, the design requirements happen to be broad enough so that more than one mask meets requirements. In those cases, one mask maximizes the number of hosts per subnet by maximizing the number of host bits. Conversely, one mask maximizes the number of subnets (and minimizes the number of hosts per subnet) by maximizing the number of subnet bits. So, if you decide that more than one mask meets the other requirements, still pick only one mask based on this last tidbit of information.

To answer each problem, supply the following information. You can use prefix style masks or dotted decimal masks, but I will use prefix style. Also, if no masks at all meet the requirements, then just say “none” or the equivalent in the answer table.

#### Table 1: Sample Answer Table

 Problem Range of Masks Chosen Mask . . .

## How Much Time?

When learning how to find the right mask, it does not matter how long you take, as long as you keep improving your understanding. At some point, you will become comfortable enough to focus on speed, because the exam is of course a timed event.

So, before looking further down in this post, start your timer, even if you are learning. It will give you an idea of where you sit. Feel free to log your time, per problem, in this poll.

That’s it. Look at the clock, and get ready to scroll down!

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## Mask Design, Drill 2: 3 Problems

Ready, steady, go!

#### Table 2: Mask Design Problems, Drill 2

 Class Maximum Subnets to Support Maximum Hosts/Subnet to Support Maximize Subnets or Hosts? 1 A 1000 1000 Hosts 2 B 100 100 Subnets 3 C 7 7 Hosts
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April 24, 2012 7:01 am

[…] post just lists the answers to the Mask Design drill #2. The drill lists some basic requirements for a number of hosts per subnet, and a number of subnets, […]