ANS-C01 Network Implementation Practice Question
A company is using AWS Transit Gateway to connect multiple VPCs and on-premises networks. They have a VPC with a CIDR of 10.0.0.0/16 attached to the transit gateway. They also have a Direct Connect virtual interface attached to the transit gateway. The on-premises network can reach some VPCs but not the VPC with CIDR 10.0.0.0/16. The transit gateway route table has a static route for the on-premises CIDR and a route propagation from the VPC attachment. What is the most likely issue?
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 CIDR overlaps with the on-premises CIDR
The most likely issue is that the VPC CIDR (10.0.0.0/16) overlaps with the on-premises CIDR. When CIDR blocks overlap, the transit gateway cannot distinguish between destinations in the VPC and on-premises, leading to routing conflicts. This explains why the on-premises network can reach other VPCs with non-overlapping CIDRs but not this VPC. The static route for the on-premises CIDR and the propagated route from the VPC attachment both exist in the transit gateway route table, but the overlap causes the transit gateway to forward traffic inconsistently or drop it. Options A, C, and D are incorrect: A) The transit gateway has no such attachment limit; C) The route table does have a route to the on-premises network via the static route; D) The VPC attachment is associated and propagating routes.
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 transit gateway has reached the maximum number of attachments
Why it's wrong here
Not mentioned.
- ✓
The VPC CIDR overlaps with the on-premises CIDR
Why this is correct
Overlapping CIDRs cause routing issues in a transit gateway.
- ✗
The transit gateway route table does not have a route to the on-premises network
Why it's wrong here
It has a static route for on-premises.
- ✗
The VPC attachment is not associated with the transit gateway route table
Why it's wrong here
It is attached and propagating routes.
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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.