I received some excellent responses to last week\u2019s newsletter asking just how relevant Jumbo Frames are today - so I\u2019d like to share them with you now.Many readers brought up this downside of Jumbo Frames: They can get in the way of convergence. If you are sending voice traffic, or something else that is time-sensitive, over your network, you don\u2019t want a Jumbo Frame getting in the way of that time-sensitive data. This reader put it most succinctly:\u201cBad idea. The problem is that Jumbo Frames create latency. Once a \u2018big guy\u2019 gets on the wire, he occupies it for a relatively longer period of time, preventing access to others, creating latency. This is one area where ATM had an advantage, giving access to the wire in short order, to high-priority users when needed.\u201dAnother reader suggested that Jumbo Frames could work in a network that is separated from the rest, so they don\u2019t get in the way of other traffic. One example might be a storage-area network.However, there may no longer be an advantage to using Jumbo Frames in the first place. A couple of readers at universities indicated they have tested Jumbo Frames to see if they actually increase performance. One writes:\u201cAfter extensive testing, we've concluded that there is very little performance gain with modern PCs and Gigabit NICs. The primary advantage in years past was reducing the impact of the high rate of interrupts. But 3-GHz CPUs have enough power to handle Gigabit streams, and NIC cards and drivers no longer require one interrupt per packet. We agree that Jumbo Frames sound like a good idea on paper, but provide little utility in practice at 1 Gigabit. 10 Gigabit may be another issue.\u201dAnother writes:\u201cWe found that it is not the protocol processing overhead that kills the performance but the latency and impact of data movement between the CPU and the NIC buffers. Because of larger DMA size the CPU spends less time setting up DMA and other stuff. Also the latency is reduced. With increasing CPU speeds, protocol-processing overhead matters less and less. Our conclusion, if a standard commodity NIC allows huge DMA transfers in one shot you can have more performance gains. At the same time, you don't need to tweak the MTU size and break the standards.\u201dLastly, one reader (at a vendor) brought up several downsides to using Jumbo Frames. First, bigger frames mean that if you lose a frame, it\u2019s a more significant network event, and retransmitting lost packets becomes a more time-consuming deal. Second, everything in the network must support Jumbo Frames for it to work. And thirdly, Internet connections don\u2019t support Jumbo Frames:\u201cA frame bigger then the one supported by the Internet connection will be fragmented before it\u2019s sent, highly reducing the performance and reliability of the Internet connection. This results in a requirement that every workstation must know which packets go to the local network and which go to the Internet. To detect the maximal packet size on a connection, the IP implements the MTU path discovery algorithm, but this is not standardized, and many firewalls don\u2019t allow the ICMP packets related to this algorithm to pass through, due to denial-of-service attacks. So, Jumbo Frames can\u2019t be implemented in a network connected to the Internet.\u201dBig thanks to everyone who wrote in with such thoughtful comments on this topic.