A analytics platform moved inter-VPC traffic from VPC peering to a transit gateway. The instances were tuned years ago for jumbo frames and still advertise a 9001-byte interface MTU. Small requests and SSH sessions work, but bulk transfers between the two VPCs now stall part-way through, and packet captures show large frames leaving the source and never arriving. Which change resolves this?
- A.
Raise the transit gateway MTU to 9001 in the attachment options and restart the affected instances so the new value is picked up.
- B.
Add a static route for each VPC CIDR in the transit gateway route table so large frames are no longer sent to a propagated route.
- C.
Enable appliance mode on both transit gateway VPC attachments so that each flow is pinned to one Availability Zone.
- D.
Lower the interface MTU on instances in both VPCs to the maximum the transit gateway supports, and change both VPCs together.
Show answer
Answer: D
A transit gateway carries a smaller maximum frame than VPC peering, so instances still set to the peering-era MTU have their large frames silently discarded.
- A. The transit gateway's maximum frame size is a service property and cannot be raised in attachment options.
- B. Static versus propagated routes change which attachment is chosen, not the maximum frame the path will carry.
- C. Appliance mode pins a flow to one Availability Zone for stateful appliances; it has no effect on frame size.
- D. Aligning the instance MTU with the transit gateway's supported maximum removes the oversized frames, and changing both VPCs together avoids a mismatch.