UK How jumbo frames work
Jumbo frames are Ethernet frames larger than the size set by the IEEE 802.3 standard. A standard frame carries at most 1,500 bytes of data, its MTU, inside a frame of 1,518 bytes, or 1,522 bytes with a VLAN tag. A jumbo frame raises that limit, most commonly to an MTU of 9,000 bytes. Frames slightly over the standard size, around 1,600 bytes, are sometimes called baby giants and mainly make room for extra tags.
The 1,500-byte limit dates from early Ethernet, when memory was expensive and links were slow. Gigabit and faster links made it look small: at 1 Gb/s a full stream of standard frames is more than 80,000 frames a second, and each one costs the sending and receiving computers some processing. Jumbo frames move the same data in about a sixth as many frames.
Jumbo frames are not part of IEEE 802.3. They are an extension that network card, switch and operating system makers support, so there is no single maximum. Most equipment accepts a 9,000-byte MTU, and many switches allow frames of around 9,200 to 10,000 bytes. Sizes much above that are rare, partly because the 32-bit CRC that checks every Ethernet frame for errors becomes less reliable on frames over about 12,000 bytes.
Jumbo frames vs standard frames
The benefit is easiest to see per frame. The table assumes TCP over IPv4 on a 1 Gb/s link, counting the preamble, header, checksum and inter-frame gap that every frame carries on the wire.
| MTU | Frame on the wire | TCP data per frame | Efficiency | Frames per second at 1 Gb/s | Time on a 1 Gb/s link |
|---|---|---|---|---|---|
| 1,500 (standard) | 1,538 bytes | 1,460 bytes | Around 94.9% | Around 81,300 | Around 12.3 µs |
| 9,000 (jumbo) | 9,038 bytes | 8,960 bytes | Around 99.1% | Around 13,800 | Around 72.3 µs |
| 9,216 (common switch maximum) | 9,254 bytes | 9,176 bytes | Around 99.2% | Around 13,500 | Around 74.0 µs |
The gain in raw efficiency is only around four percentage points. The bigger win is the sixfold drop in frames per second, because each frame means interrupts, buffer handling and protocol work in the receiving computer. At 10 Gb/s the frame rates are ten times higher, so the saving matters even more.
When to use jumbo frames
Jumbo frames help where large amounts of data move steadily between a few known devices on a network you control.
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Machine vision. GigE Vision cameras stream image data continuously, and setting the camera’s packet size to around 8,000 to 9,000 bytes is standard practice to lower processor load and avoid dropped packets.
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Storage and backup. iSCSI, NAS traffic, video recording and backups between servers and storage.
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Server and virtualisation links. Data-centre style links between hosts, such as virtual machine migration and cluster traffic.
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Video capture and analytics. Uncompressed or high-bit-rate video moved between capture computers and analytics servers.
When to leave jumbo frames off
Jumbo frames are not a general speed setting. They add nothing on links that carry small packets, and they cause faults when only part of the path supports them.
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Mixed or unknown paths. A switch drops a frame larger than it accepts, usually without any error message, so a single device left at 1,500 bytes breaks large transfers while small ones still work.
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The internet. Internet paths use a 1,500-byte MTU, so jumbo frames only make sense inside a local network or VLAN.
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Control traffic. PLC, Modbus TCP and EtherNet/IP cyclic data is typically tens to a few hundred bytes per packet, so jumbo frames do not speed it up.
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Latency-sensitive ports. A 9,000-byte frame occupies a 1 Gb/s link for around 72 µs, so time-critical frames can wait behind it. Keep control traffic on its own VLAN or port, or use priority queues.
How to enable jumbo frames
Set the same size end to end: on the network card or frame grabber in each computer, on every switch port in the path and, for vision, on the camera. Note that vendors count differently. Some settings refer to the IP MTU, others to the full frame including headers, so a switch is usually set slightly higher than the computers, for example a 9,216-byte frame size for a 9,000-byte MTU. Test with a large ping that is not allowed to fragment before going live.
Our Ethernet and PoE frame grabbers include Intel I210 and E610 based cards that list jumbo frames up to 9,728 bytes, and many of our unmanaged industrial switches list jumbo frame support, typically at around 9 KB to 10 KB, so a small camera network can run jumbo frames without a managed switch. Our guides to network interface cards and 10GbE networking cover the rest of the link.
Quick answers on jumbo frames
Jumbo frames: common questions
Should I enable jumbo frames?
Only if every device on the path supports them. They help steady bulk traffic such as cameras and storage on a network you control. For a home or office network with mixed devices, leave them off.
Is a jumbo packet the same as a jumbo frame?
Yes, in practice. Windows network card settings often say jumbo packet, while switches say jumbo frame. Both mean raising the Ethernet frame size above the standard limit.
Do jumbo frames improve performance?
For bulk transfers, often yes. They reduce processor load and frame rate, which can prevent dropped packets on busy camera or storage links. They do little for web, control or small-packet traffic.
What is MTU 9000?
A 9,000-byte maximum IP packet size. It is the most common jumbo frame setting, and all devices on the same network segment should use it.
What happens if jumbo frame sizes do not match?
Large frames are dropped. Small packets still pass, so the network looks healthy while big transfers stall or time out, which makes mismatches hard to spot.
We fit frame grabbers and network cards in our vision and edge AI computers as standard, and we set the MTU on the computer, switch and cameras to match before the system ships.