Testing Jumbo Frames with ENA on Windows EC2 instances

Question

I have enabled Jumbo frames on 2 EC2  (M5 and R5D sizes) **Windows server 2019 instances** with ENA, the instances are in the same subnet and I have put them in a cluster placement group for good measure. I used the command `Set-NetAdapterAdvancedProperty -Name "Ethernet" -RegistryKeyword "*JumboPacket" -RegistryValue 9015` to enable jumbo frames. I additionally also ran the command `netsh interface ipv4 set subinterface "Ethernet" mtu=9001`

However, when I try to ping one instance from another using the jumbo frame packet size on the public IP, using the command below, I am still seeing that packet are dropped. Security groups have the ICMP traffic enabled and ping works with regular packet sizes.

`Ping xx.xx.xx.xx -f -l 9000`

**Packet needs to be fragmented but DF set.**

**Packets: Sent = 4, Received = 0, Lost = 4 (100% loss)**

Can anybody suggest what I may be missing here?

Accepted Answer

Jumbo frames won't work over public IPs as that goes through an Internet Gateway. You need to use the private IP for Jumbo Frames to be utilized. More information can be found at: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/network_mtu.html#jumbo_frame_instances.

Testing Jumbo Frames with ENA on Windows EC2 instances

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