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Archive 1

Clean up

I'm cleaning this up, as it is somewhat wrong in places (eg, the ethernet MTU is not 1518 bytes, that is the total ethernet frame size not the ethernet payload size, which IP names the MTU). I've also added how 9000 became the conventional jumbo frame MTU and why IEEE have no interest in a standard jumbo frame size. Please forgive the lack of citations as I do so. Gdt 14:09, 6 July 2007 (UTC)

TP hubs are little computers with multiple NICs

"When a twisted pair or fiber link segment is used and neither end is connected to a hub, full-duplex" is nonsense. A hub is like a PC with multiple NICs in crossover mode and set to forward packets. Half duplex is required on coax, not with separate receive and transmit twisted pairs. Some older NIC chips were too slow or not enough ram or bad drivers, ran half duplex. Again, the TX/RX wires don't touch, collisions are actually handled in Hub firmware.

Shjacks45 (talk) 17:04, 9 December 2007 (UTC)

Sorry

posted on wrong page.

I did get a support call for a customer that was trying to use frames larger than supported by his NIC card driver. PCI resources on one of my machines NICs, largest memory setaside is 64K.

Shjacks45 (talk) 17:18, 9 December 2007 (UTC)


Notes

The format of the jumbo frame is described here. http://rtg.ietf.org/~fenner/ietf/isis/html-archive/2001-06/msg00033.html

The maximum length of traditional frames has to do with the initial ethernet protocol before the 802 standard. From memory the length was added to what was the type field, the maximum length was determined by types that were in use before the standard, the article may be right because it mentions a figure greater than 1500 as the original datagram length. I think in effect the jumbo frame proposal is going back to what was before the 802 standard. I have to dig out old documents to give refs and check all this out.

Ok the reason for the original restriction is given; sorry is sort of given in Ethernet so that is not lost history.

  • DIX it's a type field
  • 802 first draft it's a length field
  • IETF refuse to change they have type 0x600
  • 802 change to length/type with length limited to 0x5FF (1535) for example see page 51 802.3
  • jumbo packets type changed to 0x8870
  • IEEE refuse to change.
  • Industry changes anyway.

http://www.yale.edu/pclt/COMM/ETHER.HTM

The letter rejecting the jumbo draft can be found here http://www.psc.edu/~mathis/MTU/arguments.html

The whole thing is a raging battle and we don't document any of it. http://www.psc.edu/~mathis/MTU/index.html

Charles Esson (talk) 02:24, 11 January 2008 (UTC)

Ethernet jumbo frames merge proposal

The article Jumbogram contains unrelated Ethernet jumbo frames section which should be merged into this article or deleted. --pabouk (talk) 14:05, 11 January 2008 (UTC)

I agree, it has no place here. --199.46.200.232 (talk) 21:43, 5 February 2008 (UTC)

I've gone ahead and deleted that section (there's nothing to merge -- all content there is already on this article). nneonneo (talk) 23:55, 28 March 2008 (UTC)

Bibliography

This reference ("The case for jumbo frames") requires you to pay to join the site before you're allowed to read it. Is that permissible for a WP reference? GGFSquallStrife (talk) 06:48, 30 April 2008 (UTC)

9216 magic number

Cisco, Sun and Netgear all support MTUs up to 9216 octets. Anyone know where this magic number comes from? --Kvng (talk) 15:40, 18 June 2008 (UTC)

It pretty looks like 16 × 576 bytes, where 576 is the least allowed Internet MTU size. 213.234.235.82 (talk) 13:15, 2 February 2009 (UTC)
Probably because 9216 = 9 x 1024 = 9 KiB —Preceding unsigned comment added by 194.16.221.18 (talk) 10:18, 23 November 2009 (UTC)

Ethernet and Fast Ethernet Jumbo Frames Misleading

I find this comment in the article misleading: "Many Gigabit Ethernet switches and Gigabit Ethernet network interface cards support jumbo frames, but all Fast Ethernet switches and Fast Ethernet network interface cards support only standard-sized frames"

Some devices support larger MTUs on ports running at Ethernet and Fast Ethernet speeds. I've managed to capture 1550 byte jumbos forwarded by a Cisco 3750E port running at 100Mbps on a directly-attached Gigabit Ethernet card running at 100 Mbps.

"Catalyst 3750/3560 Series switches support an MTU of 1998 bytes for all 10/100 interfaces" http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml — Preceding unsigned comment added by 212.183.128.6 (talk) 22:34, 20 August 2011 (UTC)

Thanks for pointing this out. I've removed the erroneous statement and composed a new one using your link above as a reference. --Kvng (talk) 20:03, 22 August 2011 (UTC)

Exact size of Jumbo frames

When discussing standard Ethernet frames, the values 1500 (L3 packed size) and 1518/1522 (L2 frame size) are used interchangeably. What about Jumbo frames? Are whey exactly 9000 bytes in size (or whatever multiple of 1000 or 1500), or may it be only the payload? In some driver settings they figure as “6KB MTU”, for example.

Does the Jumbo packet size must be a multiple of 1500? For example, some network cards allow to chose from {3KB, 4KB, 5KB, 6KB, 7KB}. Is it actually 3000, 4000, 5000, 6000 and 7000 bytes, or is it 3000, 4500, {5K doesn't fit in}, 6000 and 7500 bytes? Or may it be 3072, 4096, 5120, 6144 and 7168 bytes? Another common example is 16'000 bytes — clearly not 10×1500, neither 11×1500 (or may it be 16K = 16500 bytes = exactly 11×1500?). User:Kvng mentions another odd value of 9216, which is more like 6×1536 or, more likely, 16×576.

Can a single frame hold several packets? For example, we could use large segment offload (aka TCP large send) to chunk the stream into 1500-byte packets for easy transmission over low-MTU links and then still combine them into a single Jumbo frame of 9000 or 15'000 bytes to deliver from local machine to a router, where they are gated one by one. Thus we are still overwhelmed with TCP and IP tasks, but at least save resources at Ethernet layer. 213.234.235.82 (talk) 13:17, 2 February 2009 (UTC)

It looks like there is no common way to identify Jumbo frames either by actual frame size or by payload (MTU). Furthermore, when a value is referred to as “9K”, it can really mean neither 9000 nor 9216 octets, but 9014 (for example). In general, frame size could be absolutely arbitrary between minimum and maximum supported by hardware and software. Moreover, it can be different for inbound and outbound streams, and can extend slightly beyond that is offered by Windows driver: for example, 7200 octets instead of default 7154 (7142 for downstream) that is referred to as “7K”.
Combining multiple packets / segments into single Jumbo frame seems to be impossible in practice. “Path MTU discovery” algorithms always bend the stream towards the least supported packet size in the path, i. e. the largest packet size that doesn't require fragmentation.
Maybe someone should include this information into the article — after finding some references (my results are purely empiric). 213.234.235.82 (talk) 17:44, 10 February 2009 (UTC)
We've got a severe mixup here of physical frame size and MTU which is the payload the frame can carry (i.e. without the Ethernet frame overhead of 18/22 bytes). After studying dozens of manuals, spec sheets and white papers I'm afraid this is fairly common but if you drill down deep enough you can find the exact figures at least with the large manufacturers. I'll try to correct this. Zac67 (talk) 20:51, 18 December 2013 (UTC)

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Biased advertising of LSO

Kvng: you keep reverting edits, first mine then Zac67's, preaching that LSO "solves" the problem and makes jumbo frames obsolete. Yet even that source you point at (just a random webpage with no authority at all), lists a number of issues with LSO. In fact, L{S,R}O gives more trouble than it fixes, see for example [1].

In fact, while neither jumbo frames nor L{S,R}O really caught on, let's take a look at a random new driver (dwmac-sun8i -- I care about this one as it's needed for a machine I own): has jumbo, doesn't have L{S,R}O. This is just a piece of anecdata, but it's telling. -KiloByte (talk) 00:02, 3 August 2017 (UTC)

I sense a potential WP:NPOV issue here. The sources are not good. The current POV should be retained until someone can come up with some good WP:SECONDARY sources. ~Kvng (talk) 15:48, 5 August 2017 (UTC)
Uhm, but why current (yours) POV, which I accuse of being extremely biased against Jumbo, be retained? Perhaps the wording of my edit was quite a bit biased the other way, but that doesn't make current wording any better. Heck, even deleting this section completely would be an improvement. -KiloByte (talk) 01:32, 12 August 2017 (UTC)
Please check the current wording. It just states "is an approach" and is carefully worded to not give a bias. We need RS to clarify further and since this is obviously disputed, future edits might need to reflect pros and cons. --Zac67 (talk) 07:58, 12 August 2017 (UTC)
I reviewed the recent changes and don't have a problem with this wording. ~Kvng (talk) 13:51, 15 August 2017 (UTC)

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