ANS-C01 Jumbo frames Practice Question
A global e-commerce company operates a production environment on AWS with a VPC (10.0.0.0/16) containing public and private subnets in three Availability Zones. The application runs on EC2 instances in private subnets behind an Application Load Balancer (ALB) in public subnets. The company uses AWS Transit Gateway to connect multiple VPCs and on-premises data centers via Site-to-Site VPN. Recently, the operations team noticed intermittent connectivity issues: users in the Asia-Pacific region experience slow page load times and occasional timeouts, while users in other regions have no issues. The network team suspects packet loss or high latency on the VPN connection to the on-premises data center in Singapore, which hosts a critical database. The AWS Direct Connect connection is not yet available. The team ran a traceroute from an EC2 instance in the production VPC to the database server (IP 203.0.113.50) and observed high latency and packet loss on the fifth hop (a transit gateway attachment). The VPN tunnel status shows 'UP' on both ends. CloudWatch metrics for the VPN tunnel show no errors but high 'TunnelData' bytes. What should the network engineer do FIRST to resolve the issue?
⚠ Common exam trap
Candidates might think that increasing bandwidth (option B) is the solution, but the problem is likely MTU-related packet loss, not bandwidth limitation.
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
✓
Enable jumbo frames on the transit gateway and the EC2 instances in the private subnets.
Enabling jumbo frames on the transit gateway and EC2 instances allows larger MTU, reducing packet fragmentation and the associated packet loss and latency. The high 'TunnelData' bytes and packet loss on the attachment suggest MTU mismatch. Option B is incorrect because adding a second VPN tunnel with ECMP increases bandwidth but does not fix MTU issues. Option C is incorrect because Direct Connect is not available yet and the problem is not routing. Option D is incorrect because stronger encryption does not affect MTU.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable jumbo frames on the transit gateway and the EC2 instances in the private subnets.
Why this is correct
Enable jumbo frames on the transit gateway and EC2 instances to allow larger MTU, reducing fragmentation and packet loss. This is the first step to address MTU-related issues.
- ✗
Increase the VPN tunnel bandwidth by creating a second VPN tunnel and enabling ECMP.
Why it's wrong here
Increasing bandwidth by adding a second VPN tunnel with ECMP does not resolve packet loss due to MTU mismatch; it only adds capacity.
- ✗
Modify the BGP attributes on the transit gateway to prefer the Direct Connect path once it becomes available.
Why it's wrong here
Modifying BGP attributes for Direct Connect is premature because Direct Connect is not available; the issue is likely MTU-related, not routing.
- ✗
Rebuild the VPN connection using a different customer gateway device with stronger encryption.
Why it's wrong here
Rebuilding the VPN connection with stronger encryption does not address the high latency and packet loss caused by MTU fragmentation.
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JA
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.