Subnets within a VNet in Azure - Step-by-Step Execution

Process Flow - Subnets within a VNet

Create Virtual Network (VNet)

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Define Address Space for VNet

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Create Subnet 1 with CIDR

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Create Subnet 2 with CIDR

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Assign Subnets to VNet

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VNet with multiple subnets ready for resources

This flow shows how a virtual network is created first, then divided into smaller subnetworks (subnets) with their own address ranges inside the VNet.

Execution Sample

Azure

resource "azurerm_virtual_network" "example" {
  name                = "example-vnet"
  address_space       = ["10.0.0.0/16"]
  location            = "eastus"
  resource_group_name = "example-rg"
}

resource "azurerm_subnet" "subnet1" {
  name                 = "subnet1"
  resource_group_name  = "example-rg"
  virtual_network_name = azurerm_virtual_network.example.name
  address_prefixes     = ["10.0.1.0/24"]
}

resource "azurerm_subnet" "subnet2" {
  name                 = "subnet2"
  resource_group_name  = "example-rg"
  virtual_network_name = azurerm_virtual_network.example.name
  address_prefixes     = ["10.0.2.0/24"]
}

This code creates a virtual network with a large address space, then creates two subnets inside it with smaller address ranges.

Process Table

Step	Action	Resource Created	Address Space	Subnet CIDR	Result
1	Create VNet	Virtual Network	10.0.0.0/16	N/A	VNet created with large address space
2	Create Subnet 1	Subnet	10.0.0.0/16	10.0.1.0/24	Subnet1 created inside VNet
3	Create Subnet 2	Subnet	10.0.0.0/16	10.0.2.0/24	Subnet2 created inside VNet
4	Assign Subnets	VNet with Subnets	10.0.0.0/16	10.0.1.0/24, 10.0.2.0/24	VNet now contains two subnets
5	End	N/A	N/A	N/A	Setup complete, ready for resource deployment

💡 All subnets created within the VNet address space, no overlaps, deployment ready

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
VNet Address Space	None	10.0.0.0/16	10.0.0.0/16	10.0.0.0/16	10.0.0.0/16
Subnet1 CIDR	None	None	10.0.1.0/24	10.0.1.0/24	10.0.1.0/24
Subnet2 CIDR	None	None	None	10.0.2.0/24	10.0.2.0/24
Subnets Assigned	None	None	Subnet1	Subnet1, Subnet2	Subnet1, Subnet2

Key Moments - 3 Insights

Why must subnet CIDRs be within the VNet address space?

Subnet CIDRs must fit inside the VNet address space to avoid IP conflicts and ensure all subnets belong to the same network, as shown in execution_table steps 1 to 4.

Can subnets overlap each other’s address ranges?

No, subnets cannot overlap. Each subnet must have a unique, non-overlapping CIDR block inside the VNet, as seen in steps 2 and 3 where subnets have distinct ranges.

What happens if you try to create a subnet outside the VNet address space?

The deployment will fail because Azure requires subnets to be inside the VNet’s address space, which is why step 4 confirms subnets are assigned only if they fit inside the VNet.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the CIDR of Subnet2?

A 10.0.2.0/24

B 10.0.1.0/24

C 10.0.0.0/16

D 192.168.1.0/24

💡 Hint

Check the 'Subnet CIDR' column at step 3 in the execution_table.

At which step are both subnets assigned to the VNet?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Subnets Assigned' variable in variable_tracker after each step.

If Subnet1 CIDR was changed to 10.0.2.0/24, what would happen?

A VNet address space would automatically expand

B Subnet1 and Subnet2 would overlap causing deployment failure

C Subnet1 would be created successfully with no issues

D Subnet2 would be deleted automatically

💡 Hint

Refer to key_moments about overlapping subnets and execution_table steps 2 and 3.

Concept Snapshot

Subnets within a VNet:
- Create a VNet with a large address space (e.g., 10.0.0.0/16)
- Define subnets with smaller CIDR blocks inside the VNet range
- Subnets must not overlap each other
- Assign subnets to the VNet before deploying resources
- Ensures organized IP allocation and network segmentation

Full Transcript

This lesson shows how to create a virtual network (VNet) in Azure and divide it into smaller parts called subnets. First, you create the VNet with a big address space like 10.0.0.0/16. Then you create subnets inside it with smaller address ranges like 10.0.1.0/24 and 10.0.2.0/24. Each subnet must fit inside the VNet's address space and cannot overlap with others. After creating subnets, they are assigned to the VNet. This setup allows you to organize your network and assign IP addresses properly for your cloud resources.