Jumbo frames
In the Ethernet data network, the term jumbo frames denotes non-standardized and oversized frames .
With Ethernet, the data to be transmitted is summarized in frames. The standard size for this is set at 1518 bytes in the IEEE 802.3 standard. Frames longer than this value are known as jumbo frames . Often the term Maximum Transmission Unit (MTU) is used which, however, the greatest unfragmented packet size in the higher network layer indicating and standard Ethernet corresponds to 1500 bytes (18 bytes of overhead of an Ethernet frame without IEEE 802.1Q field) .
For some applications, jumbo frames can be useful as they reduce the protocol overhead and improve efficiency. In addition, the processing overhead of the nodes involved can possibly be reduced, since fewer frames have to be processed. Such frames are not standard, and so it must be ensured that all network elements such as switches , routers etc. in a network can handle these jumbo frames and it is tested whether there is a speed advantage.
If the compatibility is not given, the affected devices may interpret the oversized frames as jabber , which is typically associated with a blockage of the data stream, or simply discard the frames.
Areas of application
A typical area of application for jumbo frames is the transmission of large amounts of data, as is the case, for example, with data backup. This should reduce the load on all components involved and maximize throughput. Fewer headers have to be generated, processed and transmitted and fewer checksums have to be calculated.
Another area of application is shifting the computing load to the edge components or tunnel edge of a network. The edge component, which couples the local network with the external network, has to recode (= fragment) all packets from jumbo frames that leave the local network on the MTU of the external destination network. You can enjoy the advantages that jumbo frames offer locally, but communication with external networks becomes significantly more "expensive", which means that a lot of overhead is generated.
When tunneling, the protocol typically consumes additional bandwidth. Either the MTU of the network has to be reduced by the header size of the tunneling protocol or the tunnel edge has to recode the frames.
To simplify the use of TCP / IP with jumbo frames, a dynamic determination of the maximum frame size can be carried out using Path MTU Discovery . If multiple routes are available, the method may not be reliable.
Fiber Channel over Ethernet (FCoE) transports Fiber Channel frames, which can contain up to 2148 bytes, packed in Ethernet frames, which can thus grow to 2166 bytes.
Use
Jumbo frames have two direct effects: the frame rate drops - depending on the hardware, this can reduce the processing load or increase the throughput - and the maximum throughput of the links increases by around 4%.
- Standard frames
MTU = 1500 bytes: (20B IP header + 20B TCP header + 1460B TCP payload) + 18B frame header / FCS + 20B preamble / IPG = 1538B total
- ⇒ 94.93%; Max. GbE throughput : 118.7 MB / s (81,274 frames / s)
- Jumbo frames
MTU = 9000 bytes: (20B IP header + 20B TCP header + 8960B TCP payload) + 18B frame header / FCS + 20B preamble / IPG = 9038B total
- ⇒ 99.14%; Max. GbE throughput: 123.9 MB / s (13,830 frames / s)
If the hardware is optimized for processing high frame rates ( large segment offload , large receive offload ), jumbo frames are of little benefit. Depending on the capabilities and age of the hardware, careful consideration should be given to transmitting jumbo frames over several hops . The entire hardware and software of the network infrastructure is optimized for the transmission of standard Ethernet frames with a size of 1518 bytes (MTU of 1500 bytes). This concerns reserve storage (buffers), intermediate storage (caches) and queues (queues) in hardware and software components. A deviation in the frame size can lead to a large number of impairments. This can result in significantly slower processing of Ethernet frames overall.