Default VPC and subnets in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Default VPC in Google Cloud Platform?

A Default VPC is a pre-created virtual network in each Google Cloud project. It allows resources to communicate easily without manual network setup.

beginner

How many subnets does the Default VPC have and where are they located?

The Default VPC has one subnet in each Google Cloud region, covering all regions by default.

intermediate

What IP range does each Default VPC subnet use?

Each subnet in the Default VPC uses a /20 CIDR block, which provides 4096 IP addresses per subnet.

intermediate

Can you delete the Default VPC in a Google Cloud project?

Yes, you can delete the Default VPC, but it is recommended to create a custom VPC before deleting it to avoid losing network connectivity.

beginner

What are the benefits of using the Default VPC?

The Default VPC simplifies setup by providing ready-to-use networking, automatic subnets in all regions, and default firewall rules for basic security.

How many subnets are created by default in a Default VPC?

A One per zone

B One per region

C Only one subnet total

D None, you must create them

The Default VPC creates one subnet in each Google Cloud region automatically.

What is the default IP range size for each subnet in the Default VPC?

A /24

B /16

C /20

D /28

Each subnet in the Default VPC uses a /20 CIDR block, giving 4096 IP addresses.

Which of the following is true about the Default VPC firewall rules?

A You must create firewall rules manually

B Default firewall rules allow all traffic

C No firewall rules are created by default

D Default firewall rules allow basic internal communication and SSH

Default firewall rules allow internal communication and SSH/RDP access for convenience and security.

Can you delete the Default VPC in your Google Cloud project?

A Yes, but only if no resources use it

B Yes, anytime without restrictions

C No, it is permanent

D Only Google can delete it

You can delete the Default VPC if no resources are using it, but it is recommended to create a custom VPC first.

Why might you want to use a Default VPC?

A It provides ready-to-use networking with subnets in all regions

B It is only for testing

C It has no firewall rules

D It requires manual setup

The Default VPC provides automatic subnets and basic firewall rules, making it easy to start using networking quickly.

Explain what a Default VPC is and how its subnets are organized in Google Cloud.

Think about how Google Cloud helps you start without manual network setup.

Describe the benefits and limitations of using the Default VPC in a new Google Cloud project.

Consider why Google provides this network by default and when you might want to change it.

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