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VLSM Step by Step

Lesson 34 of 46 in Coddy's IP Addressing and Subnetting course.

Real teams are not all the same size, so real plans use VLSM: Variable Length Subnet Masks, meaning different-sized subnets carved from one block.

The method: right-size each team, then allocate from the start of the block, largest team first, each subnet beginning exactly where the previous one ended.

From 192.168.100.0/24: Sales needs 100 hosts (a /25, taking .0 to .127), then Engineering needs 50 (a /26, starting at .128). Two teams, two right-sized subnets, no waste between them.

Challenge

Easy

Allocate from 192.168.100.0/24: Sales needs 100 hosts, Engineering needs 50. Print the two allocations in CIDR notation, Sales first.

Expected output:

192.168.100.0/25
192.168.100.128/26

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-SizingVLSM Step by StepAllocation 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