Mask Design Drill 1: Answers

 In CCENT-OLD, IPv4 Design Drills

Today’s post just lists the answers to the Mask Design drill #1. 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 an answer for each problem in an upcoming answer table. It also lists a few other key facts that are interim steps, plus a diagram that shows the main concepts behind the choices of masks.

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 1: 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 8 9 /16 – /23 /23
2 B 8 7 /24 – /25 /24
3 C 4 4 /28 /28
4 B 6 11 None None

Figure 1: Concepts Behind Drill 1, Problem 1

Figure 2: Concepts Behind Drill 1, Problem 2

Figure 3: Concepts Behind Drill 1, Problem 3

Figure 4: Concepts Behind Drill 1, Problem 4

Mask Design Drill 1
Mask Design Drill 2
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