Mask Design Drill 2: Answers
Today’s 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, and a network class. Your job: Pick the one mask that meets all the requirements. Today’s post lists the answers. My ICND1 book, Chapter 16 spells out the details. Post questions here if you have them!
A Quick Note on What’s in the Answers
The Drill asks for the one and only one prefix-style mask that meets all requirements, or “none” if no mask meets all requirements.
This post lists the answers, with other related facts, but it does not spell out exactly how to find each answer. The answer table lists the literal answer to each problem. It also lists a few other key facts related to each problem. Additionally, this post shows a diagram of the logic behind each problem. I’m leaving the explanations at that; ask questions if the concept doesn’t leap at you after seeing what’s here.
Mask Design, Drill 2: Answers
The last two columns list the literal answers as requested in the original drill post.
Table 3: Mask Design Problems: Answers
| Class | Need at Least This Many Subnet Bits | Need at Least This Many Host Bits | Range of Masks | Correct Prefix Mask | |
| 1 | A | 10 | 10 | /18 – /22 | /18 |
| 2 | B | 7 | 7 | /23 – /25 | /25 |
| 3 | C | 3 | 4 | /27 – /28 | /27 |
Figure 1: Concepts Behind Drill 2, Problem 1
Figure 2: Concepts Behind Drill 2, Problem 2
Figure 3: Concepts Behind Drill 2, Problem 3
