Default VPC and subnets in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Default VPC Subnet Regions

In Google Cloud Platform, the Default VPC is created automatically. How many subnets does the Default VPC have and where are they located?

A No subnets are created automatically; you must create them manually.

B One subnet only in the us-central1 region.

C Multiple subnets only in the us-east1 and europe-west1 regions.

D One subnet per region, covering all GCP regions by default.

💡 Hint

Think about how Google Cloud ensures network availability across regions by default.

The Default VPC includes one subnet in each GCP region, allowing resources in any region to communicate by default.

❓ service_behavior

intermediate

Behavior of Default VPC Firewall Rules

Which of the following statements correctly describes the default firewall rules applied to the Default VPC in GCP?

A Default firewall rules allow incoming SSH, RDP, and ICMP traffic from the internet.

B Default firewall rules allow all incoming traffic from any source to all instances.

C Default firewall rules block all incoming traffic by default.

D Default firewall rules allow incoming HTTP and HTTPS traffic from the internet.

💡 Hint

Consider the security posture of default firewall rules for internal and external traffic.

The Default VPC includes firewall rules that allow SSH (TCP port 22), RDP (TCP port 3389), and ICMP from the internet (0.0.0.0/0), in addition to all internal traffic within the VPC.

❓ Architecture

advanced

Impact of Deleting a Default VPC Subnet

What happens if you delete a subnet from the Default VPC in GCP?

A GCP prevents deletion of any Default VPC subnet to protect default resources.

B Only the deleted subnet is removed; other subnets and the VPC remain intact.

C The entire Default VPC is deleted automatically.

D All firewall rules associated with the Default VPC are deleted.

💡 Hint

Think about how GCP manages default resources and user modifications.

Deleting a subnet removes only that subnet. The Default VPC and other subnets remain. You can recreate subnets if needed.

❓ security

advanced

Security Risks of Using Default VPC

Which security risk is most associated with using the Default VPC without modification in a production environment?

A Default VPC firewall rules allow internal traffic but do not restrict outbound internet access, which may expose instances to external threats.

B Default VPC has no firewall rules, exposing all instances to the internet.

C Default VPC automatically encrypts all traffic, so there are no security risks.

D Default VPC disables logging, making it impossible to audit network activity.

💡 Hint

Consider what default firewall rules allow and what they do not restrict.

The Default VPC allows outbound internet access by default, which can expose instances to external threats if not properly secured.

✅ Best Practice

expert

Best Practice for Managing Default VPC in Large Organizations

In a large organization with multiple teams and projects, what is the best practice regarding the Default VPC and its subnets?

A Keep the Default VPC unchanged and rely on IAM roles to control access to resources.

B Use the Default VPC for all projects to simplify network management.

C Delete the Default VPC and create custom VPCs tailored to each team's needs with strict firewall rules.

D Merge all project networks into the Default VPC to reduce costs.

💡 Hint

Think about network isolation and security in multi-team environments.

Deleting the Default VPC and creating custom VPCs per team or project allows better isolation, security, and control over network policies.

Practice

1. What is the Default VPC in Google Cloud Platform?

easy

A. A virtual machine template for quick deployment

B. A custom network you must create manually before use

C. A storage bucket for default files

D. A pre-made network with one subnet per region and default IP ranges

Solution

1. Step 1: Understand the Default VPC concept

   The Default VPC is a network automatically created by GCP to help users start quickly without manual setup.

2. Step 2: Identify its features

   It includes one subnet in each region with default IP address ranges, ready for use.

3. Final Answer:

   A pre-made network with one subnet per region and default IP ranges -> Option D

4. Quick Check:

   Default VPC = Pre-made network with subnets [OK]

Hint: Default VPC is ready-made with subnets in all regions [OK]

Common Mistakes:

• Thinking Default VPC is a VM or storage
• Assuming you must create it manually
• Confusing it with custom networks

2. Which gcloud command lists the subnets in the Default VPC?

easy

A. gcloud compute networks subnets list --network=default

B. gcloud compute networks list

C. gcloud compute instances list

D. gcloud storage buckets list

Solution

1. Step 1: Identify the command to list subnets

   The command to list subnets requires 'compute networks subnets list' with a network filter.

2. Step 2: Specify the Default VPC network

   Using '--network=default' filters subnets belonging to the Default VPC.

3. Final Answer:

   gcloud compute networks subnets list --network=default -> Option A

4. Quick Check:

   List subnets in default network = gcloud compute networks subnets list --network=default [OK]

Hint: Use 'subnets list' with --network=default to see Default VPC subnets [OK]

Common Mistakes:

• Using 'networks list' which shows networks, not subnets
• Listing instances or storage buckets instead
• Omitting the network filter

3. Given the Default VPC has a subnet in us-central1 with IP range 10.128.0.0/20, what is the total number of usable IP addresses in this subnet?

medium

A. 4096 usable IP addresses

B. 4091 usable IP addresses

C. 4094 usable IP addresses

D. 4090 usable IP addresses

Solution

1. Step 1: Calculate total IPs in a /20 subnet

   A /20 subnet has 2^(32-20) = 4096 total IP addresses.

2. Step 2: Subtract reserved IPs in GCP subnet

   GCP reserves 5 IPs per subnet (network, gateway, broadcast, and two reserved), so usable IPs = 4096 - 5 = 4091.

3. Final Answer:

   4091 usable IP addresses -> Option B

4. Quick Check:

   /20 subnet usable IPs = 4091 [OK]

Hint: Subtract 5 reserved IPs from total in subnet range [OK]

Common Mistakes:

• Using total IPs without subtracting reserved ones
• Confusing subnet mask with number of IPs
• Ignoring GCP reserved IP addresses

4. You try to create a new subnet in the Default VPC with IP range 10.128.0.0/20 but get an error. What is the most likely cause?

medium

A. The IP range overlaps with an existing Default VPC subnet

B. The Default VPC does not allow adding subnets

C. The subnet name is invalid

D. The region is not specified

Solution

1. Step 1: Identify the type of Default VPC

   The Default VPC is an auto-mode VPC network where subnets are automatically created and managed by GCP.

2. Step 2: Understand limitations

   You cannot manually create additional subnets in an auto-mode VPC like the Default VPC.

3. Step 3: Reason about the error cause

   Trying to create a subnet with an IP range that overlaps an existing subnet in the Default VPC causes an error.

4. Final Answer:

   The IP range overlaps with an existing Default VPC subnet -> Option A

5. Quick Check:

   Subnet creation error due to overlapping IP range [OK]

Hint: Subnet creation fails if IP range overlaps existing subnet [OK]

Common Mistakes:

• Thinking IP range overlap is not the cause
• Assuming Default VPC allows manual subnets like custom VPCs
• Forgetting to specify region or using invalid name (different errors)

5. You want to create a custom VPC with subnets in three regions without overlapping IP ranges. Which approach best follows GCP best practices?

hard

A. Create multiple Default VPCs, one per region

B. Use the Default VPC and add subnets with overlapping IP ranges

C. Create a custom VPC and assign non-overlapping CIDR blocks for each subnet in different regions

D. Create subnets with the same IP range in different regions inside the same VPC

Solution

1. Step 1: Understand custom VPC subnet creation

   Custom VPCs allow you to define your own IP ranges and subnets per region.

2. Step 2: Avoid IP range overlap

   Assigning unique CIDR blocks per subnet prevents routing conflicts and follows best practices.

3. Step 3: Evaluate other options

   Default VPC cannot have overlapping subnets; multiple Default VPCs per project are not allowed; same IP ranges in one VPC cause conflicts.

4. Final Answer:

   Create a custom VPC and assign non-overlapping CIDR blocks for each subnet in different regions -> Option C

5. Quick Check:

   Custom VPC + unique CIDRs = Best practice [OK]

Hint: Use custom VPC with unique subnet IP ranges per region [OK]

Common Mistakes:

• Trying to add overlapping subnets to Default VPC
• Assuming multiple Default VPCs per project are possible
• Using same IP ranges in multiple subnets inside one VPC