ANS-C01 Network Implementation Practice Question
A company has a Direct Connect connection with a private VIF to a VPC. They have set up a Transit Gateway and attached the VPC and the Direct Connect gateway. The on-premises network can reach some VPC resources but not others. The VPC has multiple subnets with different CIDR blocks. The on-premises router is advertising the same prefixes over BGP. What is the most likely cause of the partial connectivity?
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 route tables for the subnets that cannot be reached do not have a route to the Transit Gateway for the on-premises prefixes.
The most common cause of partial connectivity in this scenario is that the VPC route tables do not have routes pointing to the Transit Gateway for the on-premises prefixes. Even if the Transit Gateway has routes, the VPC subnets must send traffic to the Transit Gateway. Option A is correct. Option B is incorrect because if the Transit Gateway route table had incorrect propagation, it would affect all prefixes equally. Option C is incorrect because the on-premises router advertising the same prefixes would not cause partial connectivity. Option D is incorrect because the Direct Connect gateway association is fine if some traffic works.
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 route tables for the subnets that cannot be reached do not have a route to the Transit Gateway for the on-premises prefixes.
Why this is correct
Without a route in the VPC subnet route table pointing to the Transit Gateway, traffic from the VPC to on-premises will not be forwarded.
- ✗
The Direct Connect gateway association with the Transit Gateway is misconfigured.
Why it's wrong here
If the association were misconfigured, no traffic would flow.
- ✗
The Transit Gateway route table does not have a static route or propagation for the on-premises prefixes.
Why it's wrong here
If some traffic works, the Transit Gateway likely has the routes; the issue is on the VPC side.
- ✗
The on-premises router is advertising different prefixes over BGP than expected.
Why it's wrong here
The question states the on-premises router is advertising the same prefixes, so this is not the issue.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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