The correct answer is to investigate the MTU settings on the on-premises router and the AWS Direct Connect interface. When DMS replication timeouts occur over Direct Connect, a mismatch in Maximum Transmission Unit (MTU) between the on-premises network and the AWS side forces packet fragmentation or, worse, silent drops, which directly causes intermittent connection failures. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how Layer 2 constraints like MTU can break higher-level replication tasks, even when routing and security groups appear correct. A common trap is to blame security groups or routing, but since Direct Connect uses a private VIF with point-to-point Layer 2 connectivity, those are irrelevant. Remember the memory tip: "MTU mismatch makes DMS ditch" — always check the frame size first when you see timeouts over a private VIF.
ANS-C01 Network Management and Operations Practice Question
This ANS-C01 practice question tests your understanding of network management and operations. 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 company is using AWS Database Migration Service (DMS) to replicate data from an on-premises Oracle database to an Amazon RDS for Oracle instance. The replication is failing intermittently with connection timeouts. The network connectivity uses a Direct Connect private VIF. What should the network team investigate first?
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
✓
The MTU settings on the on-premises router and the AWS Direct Connect interface.
Option B is correct because the MTU mismatch between on-premises and AWS can cause packet fragmentation or drops, leading to timeouts. Option A is wrong because security groups do not apply to on-premises traffic. Option C is wrong because routing is point-to-point, no internet. Option D is wrong because VPN is not used.
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.
✓
The MTU settings on the on-premises router and the AWS Direct Connect interface.
Why this is correct
MTU mismatch can cause intermittent connectivity issues, especially with DMS.
Clue confirmation
The clue word "first" in the question point toward this answer.
The security group of the RDS instance to ensure it allows traffic from the on-premises IP range.
Why it's wrong here
Security groups are for VPC resources, but the issue is intermittent, not consistent blocking.
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
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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 Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The MTU settings on the on-premises router and the AWS Direct Connect interface. — Option B is correct because the MTU mismatch between on-premises and AWS can cause packet fragmentation or drops, leading to timeouts. Option A is wrong because security groups do not apply to on-premises traffic. Option C is wrong because routing is point-to-point, no internet. Option D is wrong because VPN is not used.
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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Question Discussion
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