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Network ImplementationeasyMultiple ChoiceObjective-mapped

ANS-C01 Network Implementation Practice Question

Exhibit

Refer to the exhibit.

```
# CloudFormation snippet
Resources:
  MyVPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.0.0.0/16
  PublicSubnet:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref MyVPC
      CidrBlock: 10.0.1.0/24
      MapPublicIpOnLaunch: true
```

A network engineer created the CloudFormation stack shown. After creation, an EC2 instance launched in PublicSubnet does not have a public IP address. What is the most likely reason?

⚠ Common exam trap

The ANS-C01 exam often tests the misconception that a NAT Gateway is required for public IP assignment, but the correct requirement is an Internet Gateway attached to the VPC with a route in the subnet's route table.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

The VPC does not have an Internet Gateway attached

An EC2 instance in a public subnet requires an Internet Gateway (IGW) attached to the VPC to receive a public IP address. Without an IGW, the instance cannot be assigned a public IP or communicate with the internet, even if the subnet is configured to auto-assign public IPs. The CloudFormation stack likely omitted the IGW resource or its attachment to the VPC, leaving the VPC isolated.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • The VPC does not have an Internet Gateway attached

    Why this is correct

    Without an Internet Gateway, instances cannot be assigned public IPs or reach the internet.

  • The subnet does not have an Internet Gateway attached

    Why it's wrong here

    Internet Gateway is attached to the VPC, not the subnet.

  • The subnet's route table does not have a route to a NAT Gateway

    Why it's wrong here

    NAT Gateway is for private subnets; public subnets use Internet Gateway.

  • The instance type does not support public IP addresses

    Why it's wrong here

    All EC2 instance types support public IP assignment.

Visual reference

192.168.1.0 /24 256 addresses (254 usable) 192.168.1.0 /25 Subnet A 128 addr (126 usable) 192.168.1.128 /25 Subnet B 128 addr (126 usable) Borrowing 1 bit from host portion creates 2 subnets (/25)

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Last reviewed: Jul 4, 2026

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