ANS-C01 Question 373
Single answerYou are designing a hybrid architecture where your on-premises data center communicates with an Amazon VPC over a Site-to-Site VPN. The on-premises network has an MTU (Maximum Transmission Unit) of 1500 bytes, while the VPN connection's MTU is 1436 bytes. Users report slow performance when transferring large files from an Amazon EC2 instance in the VPC to the on-premises network. What is the MOST likely cause of the performance issue, and how can you resolve it?
- A
The difference in MTU sizes is causing packet fragmentation. Configure Path MTU Discovery (PMTUD) to detect and adjust the packet size automatically.
- B
The VPN connection does not support large file transfers. Use an AWS Direct Connect connection instead.
- C
The difference in MTU sizes is causing packet loss. Increase the MTU size of your VPC to match the on-premises network.
- D
The EC2 instance is not optimized for high performance. Use an EC2 instance with enhanced networking capabilities.
Show answer and explanation
Correct answer: A
Explanation
The issue arises from the MTU mismatch between the on-premises network (1500 bytes) and the VPN connection (1436 bytes). When packets exceed the MTU of the VPN connection, they get fragmented, which increases latency and reduces performance. Path MTU Discovery (PMTUD) allows devices to dynamically detect and adjust the packet size to avoid fragmentation, resolving the issue effectively.
- A. Correct.
Correct. The MTU mismatch between the on-premises network and the VPN connection results in packet fragmentation, which negatively impacts performance. Enabling Path MTU Discovery (PMTUD) ensures that packet sizes are automatically adjusted to avoid fragmentation.
- B. Incorrect.
Incorrect. The VPN connection supports large file transfers, but MTU mismatch is the root cause of the performance issue, not the VPN's capabilities.
- C. Incorrect.
Incorrect. Increasing the MTU size of your VPC is not possible as the VPN MTU is fixed at 1436 bytes. The issue lies in handling the MTU mismatch, not in increasing the MTU size.
- D. Incorrect.
Incorrect. While enhanced networking can improve performance, it does not address the MTU mismatch issue that is causing packet fragmentation and performance degradation.