Mask to Prefix

Lesson 11 of 46 in Coddy's IP Addressing and Subnetting course.

A mask and a prefix length are the same fact in two costumes. To go from mask to prefix, count the ones.

Full octets are easy: each 255 contributes 8. The interesting octet is the partial one. Remember the left-packed bytes from chapter one: 128 is one bit, 192 is two, 224 is three, 240 is four, 248 is five, 252 is six, 254 is seven.

So 255.255.255.192 is 8 + 8 + 8 + 2 = /26. With that little table memorized, you convert masks at a glance.

Challenge

Beginner

Convert each mask to its prefix length. Print one per line, slash included, in this order:

255.0.0.0
255.255.255.192

Expected output:

/8
/26

Try it yourself

Terminal

All lessons in IP Addressing and Subnetting

1Bits and Binary

Numbers as Bits Binary to Decimal Powers of Two Recap - Binary Warm-up

4CIDR Notation

Goodbye Classes Reading CIDR Block Sizes Recap - CIDR Reading

7Special Addresses

Private Ranges Loopback Link-Local Zero and Broadcast

10Capstone - The Office

The Floor Plan Sizing Each Team Carving the Block The Router's View Recap - Ship the Plan

2IPv4 Anatomy

Four Octets The 32-Bit View Network and Host Valid or Not Recap - Read an Address

5Inside a Subnet

Network Address Broadcast Address Usable Hosts First and Last Host Recap - Subnet Facts

8Planning Networks

Right-Sizing VLSM Step by Step Allocation Order Checking for Overlap Recap - Plan a Network

3The Subnet Mask

What a Mask DoesMask to PrefixPrefix to Mask ANDing It Out Recap - Mask Basics

6Subnetting Drills

The Block Size Trick Which Subnet Am I In Splitting a /24 Splitting Again Recap - Subnetting Drills

9IPv6 First Steps

Why IPv6 Reading IPv6 Prefixes in IPv6 Recap - IPv6 Basics

Practice on your own: Terminal playground