Usable Hosts

Lesson 21 of 46 in Coddy's IP Addressing and Subnetting course.

Since the network and broadcast addresses are reserved, the number of machines a subnet can actually hold is 2^{host bits} - 2.

A /26 has 6 host bits: 64 total, 62 usable. A /29 has 3: 8 total, 6 usable. The classic /24 has 8: 256 total, 254 usable.

The minus two hurts most in tiny subnets: a /30 spends half its four addresses on overhead. That is why point-to-point links are the only place you normally see one.

Challenge

Beginner

Print the number of usable host addresses in a /26, a /29, and a /24, one per line, in that order.

Expected output:

62
6
254

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 AddressUsable HostsFirst 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