A company runs application servers on EC2 in separate VPCs connected by a transit gateway. Instances are in private subnets with routes to the transit gateway for internal and external traffic. External traffic is inspected by firewall devices in a VPC that handle IGW traffic. The team wants to increase the per-packet payload size between EC2 instances while keeping all traffic via the transit gateway. What should the network engineer recommend?

The correct answer is to instruct the application team to set the maximum transmission unit (MTU) of the system's network interfaces to 8500 bytes. AWS Transit Gateway supports an MTU of 8500 bytes for traffic between VPCs. This allows for larger packet payloads, reducing overhead and potentially improving performance for applications that can utilize it. Enabling jumbo frames on the transit gateway is not an option; Transit Gateway has a fixed MTU of 8500 bytes for inter-VPC traffic. Setting the MTU to 9001 bytes on EC2 instances would lead to fragmentation or packet drops when traffic traverses the Transit Gateway, as it exceeds the Transit Gateway's MTU limit. Setting the MTU of the VPC is not a configurable option; MTU is configured at the instance network interface level. Enhanced networking is already a best practice for performance but doesn't directly dictate the MTU value for Transit Gateway compatibility.