ANS-C01 Network Design Practice Question
A company is designing a hybrid network architecture using AWS Direct Connect. They have a single Direct Connect connection with a private virtual interface (VIF) to a VPC in us-east-1. The on-premises network uses BGP to advertise a prefix (10.0.0.0/8) to AWS. The VPC has a CIDR of 10.1.0.0/16. The company wants to add a second VPC (10.2.0.0/16) in the same region and allow on-premises to communicate with both VPCs. They plan to use a Transit Gateway to connect the VPCs and the Direct Connect gateway. The Direct Connect gateway is associated with the Transit Gateway. The on-premises router is advertising 10.0.0.0/8. After configuration, the on-premises network can communicate with 10.1.0.0/16 but not with 10.2.0.0/16. The network engineer verifies that the Transit Gateway route table has routes for both VPC attachments and that the Direct Connect gateway is associated with the Transit Gateway. 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 Direct Connect gateway is not associated with the Transit Gateway route table that contains the 10.2.0.0/16 route
When using a Direct Connect gateway with a Transit Gateway, the Direct Connect gateway propagates routes to the Transit Gateway. The Transit Gateway route table must have a route for the on-premises prefix (10.0.0.0/8) pointing to the Direct Connect gateway attachment. Also, the Transit Gateway must propagate the VPC CIDRs to the Direct Connect gateway so that on-premises can learn them. The issue is likely that the 10.2.0.0/16 route is not being propagated to the Direct Connect gateway. This can happen if the Transit Gateway route table does not have the VPC attachment associated or if the route propagation is disabled for that VPC attachment. The engineer verified routes in the Transit Gateway route table, so the issue might be that the Direct Connect gateway is not receiving the route for 10.2.0.0/16. Typically, the Transit Gateway automatically propagates routes from attachments to the Direct Connect gateway if the route table is associated. However, if the VPC attachment is not associated with the same route table as the Direct Connect gateway attachment, propagation may not happen. The most likely fix is to ensure that both VPC attachments and the Direct Connect gateway attachment are in the same 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 Direct Connect gateway is not associated with the Transit Gateway route table that contains the 10.2.0.0/16 route
Why this is correct
If the Direct Connect gateway attachment is in a different route table, it won't propagate the VPC CIDR to on-premises.
- ✗
The Transit Gateway route table does not have a route for 10.2.0.0/16
Why it's wrong here
The engineer verified that routes exist.
- ✗
The private virtual interface is not configured to support multiple VPCs
Why it's wrong here
Private VIF can support multiple VPCs via Transit Gateway.
- ✗
The on-premises router is not advertising the 10.2.0.0/16 prefix
Why it's wrong here
On-premises does not need to advertise the VPC CIDR; it needs to receive it.
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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.