Block Sizes

Lesson 17 of 46 in Coddy's IP Addressing and Subnetting course.

How many addresses does a prefix hold? Two to the power of the host bits: 2^32-n.

A /30 has 2 host bits, so 4 addresses. A /28 has 4 host bits, so 16. A /25 has 7, so 128. Each step down in the prefix doubles the block; each step up halves it.

Careful: this is the total count, including two addresses you cannot give to machines. The next chapter deals with those two.

Challenge

Beginner

Print the total number of addresses in a /30, a /28, and a /25, one per line, in that order.

Expected output:

4
16
128

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 CIDRBlock SizesRecap - 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 Does Mask to Prefix Prefix 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