Subnet modes (auto, custom) in GCP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a VPC network with automatic subnet creation.

GCP

resource "google_compute_network" "vpc_network" {
  name                    = "auto-subnet-network"
  auto_create_subnetworks = [1]
}

Drag options to blanks, or click blank then click option'

A"custom"

Btrue

C"auto"

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values instead of boolean

Setting auto_create_subnetworks to false for auto mode

Setting auto_create_subnetworks to true enables automatic subnet creation in all regions.

2fill in blank

medium

Complete the code to create a custom subnet in a VPC network.

GCP

resource "google_compute_subnetwork" "custom_subnet" {
  name          = "custom-subnet"
  ip_cidr_range = "10.0.0.0/24"
  network       = google_compute_network.vpc_network.[1]
  region        = "us-central1"
}

Drag options to blanks, or click blank then click option'

Aself_link

Bid

Cname

Dnetwork

Attempts:

3 left

💡 Hint

Common Mistakes

Using the network name instead of its ID

Using an undefined attribute

The network field expects the network's self_link to link the subnet to the VPC.

3fill in blank

hard

Fix the error in the network creation code to specify a custom subnet mode.

GCP

resource "google_compute_network" "custom_network" {
  name                    = "custom-network"
  auto_create_subnetworks = [1]
}

Drag options to blanks, or click blank then click option'

Atrue

B"auto"

C"custom"

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting auto_create_subnetworks to true for custom mode

Using string values instead of boolean

For custom subnet mode, auto_create_subnetworks must be set to false to disable automatic subnet creation.

4fill in blank

hard

Fill both blanks to create a custom subnet with the correct network reference and IP range.

GCP

resource "google_compute_subnetwork" "custom_subnet" {
  name          = "custom-subnet"
  ip_cidr_range = [1]
  network       = google_compute_network.custom_network.[2]
  region        = "europe-west1"
}

Drag options to blanks, or click blank then click option'

A"10.1.0.0/16"

Bid

Cname

D"192.168.1.0/24"

Attempts:

3 left

💡 Hint

Common Mistakes

Using network name instead of ID

Using invalid IP range format

The ip_cidr_range must be a valid CIDR block string, and network must reference the network's ID.

5fill in blank

hard

Fill all three blanks to define a VPC network in custom mode and create a subnet with a specific IP range and region.

GCP

resource "google_compute_network" "custom_network" {
  name                    = [1]
  auto_create_subnetworks = [2]
}

resource "google_compute_subnetwork" "custom_subnet" {
  name          = "custom-subnet"
  ip_cidr_range = [3]
  network       = google_compute_network.custom_network.id
  region        = "asia-east1"
}

Drag options to blanks, or click blank then click option'

A"custom-vpc-network"

Bfalse

C"10.2.0.0/20"

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Setting auto_create_subnetworks to true for custom mode

Using invalid IP range format

Using network name incorrectly

The network name is a string, auto_create_subnetworks is false for custom mode, and the subnet IP range is a valid CIDR string.

Practice

1. What happens when you create a VPC network in auto subnet mode in GCP?

easy

A. Subnets are automatically created in all regions with predefined IP ranges.

B. No subnets are created; you must create them manually.

C. Only one subnet is created in the default region.

D. Subnets are created but without any IP ranges assigned.

Solution

1. Step 1: Understand auto subnet mode behavior

   In auto mode, GCP automatically creates subnets in every region with default IP ranges.

2. Step 2: Compare with other modes

   Unlike custom mode, auto mode does not require manual subnet creation or IP range assignment.

3. Final Answer:

   Subnets are automatically created in all regions with predefined IP ranges. -> Option A

4. Quick Check:

   Auto mode = automatic subnet creation [OK]

Hint: Auto mode means automatic subnets in all regions [OK]

Common Mistakes:

• Thinking auto mode requires manual subnet creation
• Assuming only one subnet is created
• Believing subnets have no IP ranges assigned

2. Which of the following is the correct way to create a custom subnet in GCP using gcloud CLI?

easy

A. gcloud compute networks subnets create my-network --subnet-mode=custom

B. gcloud compute networks create my-network --subnet-mode=auto

C. gcloud compute networks create my-subnet --range=10.0.0.0/24

D. gcloud compute networks subnets create my-subnet --network=my-network --range=10.0.0.0/24

Solution

1. Step 1: Identify command to create a subnet

   The command to create a subnet is gcloud compute networks subnets create with network and IP range specified.

2. Step 2: Check option correctness

   gcloud compute networks subnets create my-subnet --network=my-network --range=10.0.0.0/24 correctly uses the subnet creation command with network and IP range parameters.

3. Final Answer:

   gcloud compute networks subnets create my-subnet --network=my-network --range=10.0.0.0/24 -> Option D

4. Quick Check:

   Subnet creation uses 'networks subnets create' with range [OK]

Hint: Use 'networks subnets create' with --range for custom subnets [OK]

Common Mistakes:

• Using 'networks create' to create subnets
• Missing the --range parameter for IP range
• Confusing network and subnet names

3. Given a VPC network in custom subnet mode with two subnets:
subnet-a: 10.1.0.0/16
subnet-b: 10.2.0.0/16
What happens if you try to create a third subnet with IP range 10.1.128.0/17?

medium

A. The subnet is created successfully without issues.

B. The subnet is created but traffic is blocked between subnets.

C. Creation fails due to overlapping IP ranges with subnet-a.

D. The subnet is created but assigned a different IP range automatically.

Solution

1. Step 1: Check IP range overlap

   Subnet-a uses 10.1.0.0/16 which covers 10.1.0.0 to 10.1.255.255. The new subnet 10.1.128.0/17 overlaps this range.

2. Step 2: Understand subnet creation rules

   GCP does not allow overlapping IP ranges in subnets within the same VPC network.

3. Final Answer:

   Creation fails due to overlapping IP ranges with subnet-a. -> Option C

4. Quick Check:

   Overlapping IP ranges cause subnet creation failure [OK]

Hint: Check IP ranges for overlap before subnet creation [OK]

Common Mistakes:

• Assuming subnets can overlap IP ranges
• Thinking GCP auto-adjusts overlapping ranges
• Believing traffic is blocked but subnet created

4. You created a VPC network in custom subnet mode but forgot to create any subnets. What is the result when you try to deploy a VM instance in this network?

medium

A. The VM instance deploys successfully with an automatic subnet created.

B. The VM deployment fails because no subnet exists in the network.

C. The VM deploys but without an internal IP address.

D. The VM deploys but is not reachable from other resources.

Solution

1. Step 1: Understand custom subnet mode requirements

   In custom mode, subnets must be created manually before deploying resources.

2. Step 2: Check VM deployment dependency

   VMs require a subnet to get an IP address; without subnets, deployment fails.

3. Final Answer:

   The VM deployment fails because no subnet exists in the network. -> Option B

4. Quick Check:

   Custom mode needs subnets before VM deployment [OK]

Hint: No subnet means VM deployment fails in custom mode [OK]

Common Mistakes:

• Assuming auto subnet creation in custom mode
• Thinking VM can deploy without internal IP
• Believing VM deploys but is unreachable

5. You want to create a VPC network that spans multiple regions with subnets having specific IP ranges you control. Which subnet mode should you choose and why?

hard

A. Custom mode, because it lets you manually create subnets with specific IP ranges in each region.

B. Custom mode, because it automatically creates subnets in all regions with default IP ranges.

C. Auto mode, because it allows you to edit IP ranges after subnet creation.

D. Auto mode, because it creates subnets automatically with your chosen IP ranges.

Solution

1. Step 1: Identify requirement for specific IP ranges

   You want control over IP ranges, so automatic default ranges won't work.

2. Step 2: Choose subnet mode matching control needs

   Custom mode allows manual subnet creation with chosen IP ranges per region.

3. Step 3: Eliminate incorrect options

   Auto mode does not allow choosing IP ranges; it creates default subnets automatically.

4. Final Answer:

   Custom mode, because it lets you manually create subnets with specific IP ranges in each region. -> Option A

5. Quick Check:

   Custom mode = manual subnet creation with chosen IP ranges [OK]

Hint: Custom mode for manual subnets with specific IP ranges [OK]

Common Mistakes:

• Confusing auto mode as allowing custom IP ranges
• Thinking auto mode subnets can be edited after creation
• Believing custom mode auto-creates subnets