The answer is to enable jumbo frames on the transit gateway and the EC2 instances in the private subnets. This directly addresses the intermittent connectivity issues by allowing a larger maximum transmission unit (MTU), which reduces packet fragmentation and lowers CPU overhead when handling high data volumes, as indicated by the elevated 'TunnelData' bytes. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how MTU mismatches cause packet loss at transit gateway attachments, especially with VPN tunnels carrying large data loads—a common trap is to assume bandwidth or routing changes are needed when the tunnel status shows 'UP' and CloudWatch reports no errors. Remember the key insight: high latency and packet loss on a specific hop, combined with high data throughput, almost always points to fragmentation rather than capacity. Memory tip: "Jumbo for the jump"—when you see a hop with loss and high data, think jumbo frames to smooth the jump.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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.
Option D is correct because enabling jumbo frames on the transit gateway and EC2 instances can improve throughput and reduce latency by allowing larger MTU, which reduces the number of packets and thus CPU overhead. High latency and packet loss on a transit gateway attachment, especially with high data volume, suggests MTU issues. Option A is incorrect because while BGP attributes can influence routing, the symptoms point to MTU fragmentation rather than suboptimal routing. Option B is incorrect because increasing VPN bandwidth does not address packet loss due to MTU. Option C is incorrect because the VPN tunnel is already up and CloudWatch shows high data volume, not errors.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Increase the VPN tunnel bandwidth by creating a second VPN tunnel and enabling ECMP.
Why it's wrong here
ECMP can increase throughput but does not address MTU fragmentation causing packet loss.
✗
Modify the BGP attributes on the transit gateway to prefer the Direct Connect path once it becomes available.
Why it's wrong here
Direct Connect not yet available; BGP attributes won't solve current MTU issue.
✗
Rebuild the VPN connection using a different customer gateway device with stronger encryption.
Why it's wrong here
Encryption strength does not affect MTU or latency.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Enable jumbo frames on the transit gateway and the EC2 instances in the private subnets. — Option D is correct because enabling jumbo frames on the transit gateway and EC2 instances can improve throughput and reduce latency by allowing larger MTU, which reduces the number of packets and thus CPU overhead. High latency and packet loss on a transit gateway attachment, especially with high data volume, suggests MTU issues. Option A is incorrect because while BGP attributes can influence routing, the symptoms point to MTU fragmentation rather than suboptimal routing. Option B is incorrect because increasing VPN bandwidth does not address packet loss due to MTU. Option C is incorrect because the VPN tunnel is already up and CloudWatch shows high data volume, not errors.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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