ANS-C01 Network Design Practice Question
Exhibit
Refer to the exhibit.
AWS CLI output:
{
"Vpc": {
"VpcId": "vpc-0123456789abcdef0",
"CidrBlock": "10.0.0.0/16",
"Ipv6CidrBlock": "2001:db8:1234:1a00::/56",
"EnableDnsHostnames": true,
"EnableDnsSupport": true
},
"Subnets": [
{
"SubnetId": "subnet-1a",
"CidrBlock": "10.0.1.0/24",
"AvailabilityZone": "us-east-1a",
"MapPublicIpOnLaunch": false
},
{
"SubnetId": "subnet-2a",
"CidrBlock": "10.0.2.0/24",
"AvailabilityZone": "us-east-1a",
"MapPublicIpOnLaunch": true
}
],
"RouteTables": [
{
"RouteTableId": "rtb-main",
"Associations": [{"SubnetId": "subnet-1a"}],
"Routes": [
{"DestinationCidrBlock": "10.0.0.0/16", "Target": "local"},
{"DestinationCidrBlock": "0.0.0.0/0", "Target": "igw-12345"}
]
},
{
"RouteTableId": "rtb-custom",
"Associations": [{"SubnetId": "subnet-2a"}],
"Routes": [
{"DestinationCidrBlock": "10.0.0.0/16", "Target": "local"},
{"DestinationCidrBlock": "0.0.0.0/0", "Target": "igw-12345"}
]
}
]
}Refer to the exhibit. An EC2 instance launched in subnet-1a is unable to access the internet. Which is the most likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that a missing default route is the only cause for internet access failure, but the trap here is that even with a correct route, the instance must have a public IP (via auto-assign or Elastic IP) for the internet gateway to forward traffic back to it.
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
✓
Subnet-1a does not assign public IP addresses automatically.
If subnet-1a does not have the 'Auto-assign public IPv4 address' setting enabled, EC2 instances launched in that subnet will not receive a public IP address automatically. Without a public IP, the instance cannot communicate with the internet through an internet gateway, even if the route table has a default route (0.0.0.0/0) pointing to the internet gateway. The instance would need an Elastic IP or a public IP assigned at launch to enable internet access.
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 route table rtb-main does not have a default route to the internet gateway.
Why it's wrong here
It does have a route to igw-12345.
- ✗
The VPC does not have DNS hostnames enabled.
Why it's wrong here
EnableDnsHostnames is true.
- ✓
Subnet-1a does not assign public IP addresses automatically.
Why this is correct
MapPublicIpOnLaunch is false, so instances lack public IPs.
- ✗
Subnet-1a is not associated with any route table.
Why it's wrong here
It is associated with rtb-main.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.