An administrator is configuring a new virtual network named `vnet-shared` in an Azure subs… — Microsoft Azure Administrator (AZ-104)

An administrator is configuring a new virtual network named `vnet-shared` in an Azure subscription. The virtual network is assigned the address space $172.16.100.0/24$ . The administrator must create three subnets within this virtual network:

- `subnet-app`: Must host a backend API service that requires a minimum of $28$ usable IP addresses for virtual machines.
- `AzureBastionSubnet`: Must support the deployment of Azure Bastion using the minimum possible address space.
- `GatewaySubnet`: Must connect to an on-premises network via a VPN Gateway, using a prefix size of exactly $/27$ .

The administrator wants to define the subnets sequentially starting from the beginning of the virtual network's address space without leaving any unassigned gaps or overlapping ranges. Which of the following subnet configurations should the administrator deploy?

A
`subnet-app`: $172.16.100.0/27$
`GatewaySubnet`: $172.16.100.32/27$
`AzureBastionSubnet`: $172.16.100.64/26$
`subnet-app`: $172.16.100.0/26$
`AzureBastionSubnet`: $172.16.100.64/26$
`GatewaySubnet`: $172.16.100.128/27$ Answer
C
`GatewaySubnet`: $172.16.100.0/27$
`AzureBastionSubnet`: $172.16.100.32/26$
`subnet-app`: $172.16.100.128/26$
D
`subnet-app`: $172.16.100.0/26$
`AzureBastionSubnet`: $172.16.100.64/27$
`GatewaySubnet`: $172.16.100.96/27$

Answer

The correct subnet configuration assigns

172.16.100.0/26

to `subnet-app`,

172.16.100.64/26

to `AzureBastionSubnet`, and

172.16.100.128/27

to `GatewaySubnet`.

To support

28

virtual machines, `subnet-app` needs a minimum of

33

IP addresses after adding the

5

Azure-reserved IP addresses. The smallest CIDR block that fits this is

/26

(

64

addresses). A

/27

block only provides

27

usable addresses (

32 - 5 = 27

), which is too small. `AzureBastionSubnet` requires a minimum subnet size of

/26

. In order to align sequentially without gaps or overlaps, `subnet-app` is assigned

172.16.100.0/26

(covering

.0

.63

), `AzureBastionSubnet` is assigned

172.16.100.64/26

(covering

.64

.127

), and `GatewaySubnet` is assigned

172.16.100.128/27

(covering

.128

.159

). All starting addresses are correctly aligned to their respective block boundaries.

Step-by-Step Solution

Determine the required IP address capacity for the application subnet.

28

VM host addresses +

5

Azure-reserved addresses =

33

total IP addresses.

Azure reserves the first four IP addresses and the last IP address of every subnet for internal networking services.

Determine the minimum prefix size for the application subnet and the Bastion subnet.

Both `subnet-app` and `AzureBastionSubnet` require a minimum prefix size of

/26

/27

subnet only provides

27

usable IP addresses (

32 - 5

), which is insufficient for

28

VMs. Azure Bastion has a hard requirement for a minimum subnet prefix of

/26

Map the subnets sequentially and align them to valid CIDR block boundaries.

`subnet-app` starts at

.0/26

(range:

.0

.63

). `AzureBastionSubnet` starts at

.64/26

(range:

.64

.127

). `GatewaySubnet` starts at

.128/27

(range:

.128

.159

Each subnet's starting address must be a multiple of its size to align correctly under CIDR subnet rules and avoid overlapping errors in Azure.

Key Concept

Azure subnet sizing, reserved IP addresses, service-specific prefix requirements, and CIDR block alignment.

Estimated Time:2m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics