Question

Difficulty: MediumCreate and Configure Virtual Networks and Subnets

An administrator manages an Azure virtual network named `vnet-corp-infra` with the address space $172.20.0.0/20$ . The administrator creates a subnet named `subnet-shared-services` with the address range $172.20.15.0/29$ . The administrator states that a maximum of three virtual machine instances can be simultaneously assigned private IP addresses in `subnet-shared-services`. Is this statement true?

Answer: Answer

Answer

The statement is true.

The statement is correct because Azure virtual networks reserve five IP addresses from every subnet range. In a

/29

subnet (

8

total IPs), subtracting the

5

reserved IPs leaves exactly

3

IP addresses available for virtual machines.

Step-by-Step Solution

1

Calculate the total number of IP addresses within a

/29

subnet prefix.

A

/29

subnet contains

2^{32-29} = 8

total IP addresses.

The prefix length of 29 leaves 3 host bits (

32 - 29 = 3

), which allows for

2^3 = 8

total addresses.

2

Identify the number of IP addresses reserved by Azure in each subnet.

Azure reserves exactly five IP addresses per subnet.

Azure reserves the first four IP addresses (network address, default gateway, two DNS addresses) and the last IP address (broadcast address) of the subnet range.

3

Determine the usable IP addresses for virtual machines.

There are

8 - 5 = 3

usable IP addresses.

Subtracting the five reserved IP addresses from the total eight addresses leaves exactly three usable IP addresses.

Key Concept

Azure Subnet IP Reservations

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Topics

Create and Configure Virtual Networks and Subnets