ANS-C01 Network Management and Operations Practice Question
A company uses AWS Transit Gateway to connect multiple VPCs and on-premises networks. The network team notices that traffic between two VPCs is taking a suboptimal path, going through the on-premises network instead of staying within AWS. What is the most likely cause?
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 has a propagated route from the on-premises network with a longer prefix
When a Transit Gateway route table contains a propagated route from an on-premises network with a longer prefix (more specific) than the local VPC route, traffic destined for that specific CIDR will be sent to the on-premises network instead of using the inter-VPC route. This is because more specific routes take precedence over less specific ones. The suboptimal path occurs because the traffic is forced through the on-premises network, even though both VPCs are attached to the Transit Gateway and could communicate directly within AWS. Option A is correct. Option B is incorrect because VPC peering is not used with Transit Gateway; if peering existed, it could create route conflicts, but the scenario describes Transit Gateway. Option C is incorrect because VPC Flow Logs are for monitoring traffic and do not affect routing. Option D is incorrect because security groups are stateful firewalls that control traffic, but they do not determine routing paths; routing is controlled by route tables.
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 route table has a propagated route from the on-premises network with a longer prefix
Why this is correct
More specific routes override default routes, sending traffic on-premises.
- ✗
The VPCs are also peered directly, creating a conflict
Why it's wrong here
VPC peering is separate; Transit Gateway routes take precedence with longest prefix match.
- ✗
VPC Flow Logs are enabled, causing latency
Why it's wrong here
Flow Logs do not affect routing.
- ✗
Security groups are blocking direct traffic between VPCs
Why it's wrong here
Security groups filter traffic, not route.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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