ANS-C01 Network Implementation Practice Question
Exhibit
Refer to the exhibit.
CloudFormation snippet:
Resources:
MyTransitGateway:
Type: AWS::EC2::TransitGateway
Properties:
AmazonSideAsn: 64512
AutoAcceptSharedAttachments: disable
DefaultRouteTableAssociation: enable
DefaultRouteTablePropagation: enable
DnsSupport: enable
VpnEcmpSupport: enable
MyVpcAttachment:
Type: AWS::EC2::TransitGatewayAttachment
Properties:
SubnetIds:
- subnet-abc
- subnet-def
TransitGatewayId: !Ref MyTransitGateway
VpcId: vpc-12345Refer to the exhibit. After deploying this CloudFormation stack, the VPC is attached to the transit gateway. However, routes are not being propagated to the transit gateway route table. What is the most likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the distinction between transit gateway attachment and route propagation, trapping candidates who assume that simply attaching a VPC to a transit gateway automatically populates the route table with the VPC's CIDR.
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 transit gateway route table propagation is not configured.
The exhibit shows a transit gateway route table attached to the VPC, but no propagation is configured. Without explicit propagation, the VPC attachment's CIDR blocks are not automatically added to the transit gateway route table. The CloudFormation resource AWS::EC2::TransitGatewayRouteTablePropagation must be declared to enable route propagation from the VPC attachment into the transit gateway route table.
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 attachment is not in the 'available' state.
Why it's wrong here
The attachment would fail if not available.
- ✓
The transit gateway route table propagation is not configured.
Why this is correct
DefaultRouteTablePropagation enables automatic propagation, but the attachment does not explicitly propagate.
- ✗
VPN ECMP support is enabled, preventing propagation.
Why it's wrong here
ECMP support does not block propagation.
- ✗
DNS support is disabled on the transit gateway.
Why it's wrong here
DNS support does not affect route propagation.
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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.