Even though the jumbo frame and the possible gain and risk trade-offs discussion is not new, we found ourselves discussing it yet again. Because we had different opinions, it seems like a good idea to elaborate on this topic.
Let’s have a quick recap on what jumbo frames actually are. Your default MTU (Maximum Transmission Unit) for a ethernet frame is 1500. A MTU of 9000 is referred to as a jumbo frame.
Jumbo frames or 9000-byte payload frames have the potential to reduce overheads and CPU cycles.
Typically, jumbo frames are considered for IP storage networks or vMotion networks. A lot of performance benchmarking is already described on the web. It is funny to see a variety of opinions whether to adopt jumbo frames or not. Check this blogpost and this blogpost on jumbo frames performance compared to a standard MTU size. The discussion if ‘jumbo frames provide a significant performance advantage’ is still up in the air.
There are other techniques to improve network throughput and lower CPU utilization next to jumbo frames. A modern NIC will support the Large Segment Offload (LSO) and Large Receive Offload (LRO) offloading mechanisms. Note: LSO is also referenced as TSO (TCP Segmentation Offload). Both are configurable. LSO/TSO is enabled by default if the used NIC hardware supports it. LRO is enabled by default when using VMXNET virtual machine adapters.
Risks?
Let’s put the performance aspects aside, and let us look into the possible risks involved when implementing jumbo frames. The thing is, in order to be effective, jumbo frames must be enabled end to end in the network path. The main risk when adopting jumbo frames, is that if one component in the network path is not properly configured for jumbo frames, a MTU mismatch occurs.
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