Understanding jumbo Frame

I often see the support for Jumbo frame in the vswitch and nic instructions, but I have never understood how to use jumbo frame (jumbo frame) over Ethernet. Today I found 2 images on the Internet, I believe that after reading this article, you will be rewarded.
---- This is a vendor-standard ultra-long frame format designed specifically for Gigabit Ethernet, which has not yet been recognized by the IEEE Standards Board. The maximum frame length of the Ethernet standard is 1518 bytes, while the jumbo frame length varies from 9000 bytes ~ 64000 bytes. Jumbo frame can make full use of Gigabit Ethernet performance and improve data transmission efficiency by 50% ~ 100%. In the application environment of network storage, Jumbo frame has more extraordinary significance.
---- Jumbo frame must be supported on two communication ports (switch port or Nic port) for mutual communication, and is not compatible with earlier Ethernet products, therefore, it is mainly used to connect Gigabit trunk ports and server ports to the trunk links of the network. When a switch forwards data in jumbo frame format to a port that is not compatible with jumbo frame, it must convert the data in jumbo frame format to a standard Ethernet frame format, to ensure normal operation. On the contrary, when a port that is not compatible with jumbo frame forwards data to a port that supports jumbo frame, the switch can combine multiple standard Ethernet frames into ultra-long jumbo frame frames to improve transmission efficiency. ---- Jumbo frame has not become an international standard. Currently, only some manufacturers support this frame format. However, with the development of Ethernet to gigabit and 10g, a super-long frame format must be created. Therefore, it is very likely that jumbo frame will change from vendor standard to international standard.
---- Problems faced by jumbo frame (reproduced from anheng)
Generally, Jumbo frame is considered as a relatively simple technology and should be widely used in Lan, but this is not the case.
It should be said that jumbo frames are very useful in some fields and are intended to be designed to accelerate the transmission of large files. The maximum frame length defined in the Ethernet standard is 1518 bytes, so a large file needs to be chopped into several blocks and put into multiple Ethernet frames. When each data block is transmitted, the overhead and tail of the frame will be introduced. If a large frame can be used for file transmission, the overhead of many frames will be reduced and the Network Utilization and transmission rate will be improved. People usually think that the biggest application bottleneck of this technology is that there is no standardization so far.
However, some people do not think so, and many people have put forward the following Disadvantages of ultra-long frames: they may become an obstacle to network convergence. If people transmit voice or other content that is sensitive to latency over the network, they do not need to interfere with the transmission of these ultra-long frames of sensitive data. For example, a long frame may cause a delay. Once a 'big guy 'is transferred online, it will occupy the line for a long time and prevent others from using the line, resulting in a delay.
Another reader mentioned that ultra-long frames can be used in a network isolated from other networks, so they do not interfere with other transmission streams. The storage area network may be such an example.
However, using ultra-long frames is no longer an advantage. Two users from the university said they tested ultra-long frames to learn whether ultra-long frames can actually improve performance. One user said: "After a comprehensive test, we have concluded that the performance has improved little when using modern PCs and gigabit NICs. The main advantage of ultra-long frames in the past is to reduce the impact of high interruption rates on computers. However, the 3-GHz CPU is capable of handling 1 Gbit/s of traffic, and the nic and driver no longer need to interrupt every packet. We think that ultra-long frames are a good idea in theory, but they are of little use in the case of gigabit frames. 10G Ethernet may be another problem.
Another user said, "We found that the reason for performance reduction is not the protocol processing overhead, but the latency and impact of data movement between the CPU and the NIC buffer. The larger the size of DMA (Direct Memory Access), the less time the CPU spends setting DMA and other things, and the less latency. As the CPU speed increases, the protocol processing overhead becomes increasingly insignificant. Our conclusion is that if the standard commercialized Nic allows ultra-long DMA transmission, you can gain a higher performance gain. At the same time, you do not have to modify the MTU (maximum transmission unit) size to break the standard. "
Finally, a vendor mentioned several disadvantages of using a giant frame. First, the longer the frame, the more serious a network event will be if one frame of data is lost, and it is more time-consuming to re-transmit the lost data packets. Second, everything in the network must support ultra-long frames before they can be used. Third, Internet connections do not support ultra-long frames. A frame whose length exceeds the length supported by Internet connections is segmented before transmission, which greatly reduces the performance and reliability of Internet connections. This requires every workstation to know which data packet is sent to the local network and which data packet is sent to the Internet. In order to detect the maximum packet length on the line, the IP address executes the MTU routing detection algorithm. However, this is not a standardized method, and because of denial-of-service attacks, many firewalls Do Not Allow ICMP packets related to this algorithm to pass through. Therefore, ultra-long frames cannot be used in networks connected to the Internet.
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There are not many discussions on Jumbo frames in China. Some people of insight in China have a positive attitude towards its application, but they have made suggestions on its usage.
Mr. Cai Changxin, a fluke company, has an interesting view. He has two views on Jumbo frames. First, he believes that the choice of frame size actually reflects a control over the link reliability in the data communication process. If the link is very clean and there are few errors, this link can transmit very large frames without any system overhead. But the question is, do people think their links are in good condition and trust their link conditions.
On the other hand, what kind of data is being transmitted on a link. If real-time application data and latency-insensitive data are transmitted on a link, Jumbo frame usage, it will greatly affect real-time applications (Mr. Cai used the word "kill" here ). He believes that jumbo frames are very useful for some purely large file transmission applications, such as San. However, if there is no end-to-end QoS policy or bandwidth allocation setting in a multi-application hybrid transmission environment, the wide use of jumbo frames is irrational.
Another friend from the manufacturer also expressed his opinion. He believes that if he wants to enjoy the benefits of jumbo frames, he needs an end-to-end support for Jumbo frames, otherwise, frame re-cutting is required in some places, and more overhead will also be introduced.
On the other hand, supporting jumbo frames requires new hardware, but this is also a headache. This also causes jumbo frames to be used only in some special environments, such as data transmission on the server farm.
He personally believes that jumbo frames are advantageous in the long term, and many applications will benefit from them not only in IP Storage. In addition, there are more and more jumbo frames supported by new devices, and end-to-end support is promising. He particularly stressed that end-to-end use is meaningful.
In addition, he also said that at a distance of 1000, we calculated the transmission time of 9 K bytes of long frames. on the high-speed network, it is not as worried as some people, will introduce a huge delay.