Detailed explanation of Jumbo Frames

This issue will explain "Jumbo Frame" in detail.
1. What is Jumbo Frame?
Jumbo Frame is a vendor-standard extra-long frame format. The maximum frame length of Ethernet standard is 1518 bytes.

Different from the Ethernet standard frame length, the length of Jumbo Frame varies from vendor to vendor, ranging from 9000 bytes to 64000 bytes.
The use of Jumbo Frame can fully utilize the performance of Gigabit Ethernet and increase data transmission efficiency by 50% to 100%. In the application environment of network storage, Jumbo Frame has an extraordinary significance. Currently, the segment from 1500Byte to 9000Byte is usually called Jumbo frames, and the segment from 9000Byte to 64000Byte is called Super jumbo frames.

2. What are the advantages and disadvantages of jumbo frames?
1. Advantages: It can improve network throughput and efficiency

Small data packets are not efficient when encapsulating the second layer header, and at the same time reduce the CPU burden of the device. For small packets, the CPU spends a lot of time to fragment and reassemble packets.

Jumbo frames need to be supported on two communication ports (switch ports or network card ports) that communicate with each other, and are incompatible with previous Ethernet products. Therefore, they are mainly used between ports of gigabit trunks and links from server ports to network trunks.

When the switch transfers data in the Jumbo Frame format to a port that is not compatible with Jumbo Frame, it should convert the frame format, that is, convert the data in the Jumbo Frame format into the frame format of the standard Ethernet network, so as to ensure its normal operation. On the contrary, when transferring data from a port that is not compatible with Jumbo Frame to a port that supports Jumbo Frame, the switch can merge multiple standard Ethernet frames into an extra-long Jumbo Frame frame, thereby improving transmission efficiency.

2. Disadvantage: There are new compatibility issues
Since Jumbo Frame is a standard for various manufacturers, if the maximum length of Jumbo Frame supported by various manufacturers is inconsistent, it may cause abnormal data transfer on the link.



3. What are the typical applications of jumbo frames?
Some industrial camera scenes and large file transfer and copying scenes can improve transmission efficiency by using jumbo frames.

4. FAQs and notes
1. How to understand the difference between the maximum data transmission of 1500Byte at the data link layer and jumbo frames?

The maximum data transmission of 1500Byte at the data link layer is the IEEE-recognized maximum data frame (MTU) under the default conditions. In the VLAN tag scenario, the maximum data packet byte length is 1522 bytes (1500+14+4+4). A jumbo frame is an Ethernet frame with a frame length greater than 1522 bytes. This is a vendor-standard extra-long frame format designed for Gigabit Ethernet. The length of jumbo frames varies by vendor, ranging from 9,000 bytes to 64,000 bytes.



2. How to confirm whether the computer network card supports jumbo frames? How to set it?
You can check whether the device has a jumbo frame option in the properties of the network card-advanced configuration interface. If there is a corresponding option, just select the corresponding value. The network card turns off the jumbo frame function by default.

3. How to confirm whether the network device (router/switch/AP) supports jumbo frames?
Jumbo frames are a function that can only be supported by switch chips. Whether different chip solutions support it needs to be checked according to the chip solution. In addition, please note: jumbo frames of switches do not support three-layer forwarding.

4. A few notes about jumbo frames:




All end-to-end transmission interfaces need to support jumbo frames to transfer jumbo frame packets from one end to the other. If the intermediate transmission device (switch) does not support jumbo frames or the maximum jumbo frame supported is smaller than the jumbo frame set by the network card, the switch will discard the packet;

TCP jumbo frame negotiation process is determined by the system MTU, and the MSS is negotiated during the handshake phase:

UDP jumbo frame transmission process, the network card directly sends UDP data packets according to the jumbo frame value:

After some network cards are installed in the system, after modifying the jumbo frames supported by the network card, the computer's default MTU will also be modified, but the system MTU of some network cards will not be modified. This can be confirmed and modified through commands (CMD in administrator mode):



Change computer mtu:

Check mtu: