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Having read up a bit about ethernet jumbo frames, I'm wondering. There seem to be technical advantages to being able to use larger than 1500 byte ethernet frames in some cases. Just enabling jumbo frames on a network card is not backward compatible and should not be done unless the entire network supports jumbo frames. I've read the IETF draft and I'm wondering why there is no autonegotiation for jumbo frames.

The latency of 9K frames on gigabit ethernet is less than that of 1500b frames on 100mbit, and technical problems such as the CRC being inadequate for large frames could also be fixed by autonegotiation. Mixing jumbo and non jumbo ethernet equipment would require a solution such as ethernet-level 'fragmentation required' messages or separate mtu discovery for every destination mac address, but it doesn't seem unsolvable.

So:

  • Other backward incompatible ethernet settings are autonegotiated, why not jumbo frames?
  • Are there technical reasons jumbo frames could not be autonegotiated?
  • Are there political or other reasons?
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closed as not constructive by Chopper3, Tom O'Connor, MikeyB, HopelessN00b, RobM Oct 2 '12 at 16:22

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You should check out this document from the Ethernet Alliance, specifically the section about "Jumbo Frame Enablement" where they say "MTU discovery along Layer 2 pathways must be supported … a purely Layer 2 mechanism has not been standardized." -- That would be the nail in the coffin right there. –  voretaq7 Oct 2 '12 at 16:26
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Jumbo frames are not approved for Ethernet by the IEEE (the relevant standards body). It is a "vendor" extension without standardization (in the stricter sense of the word, as the industry has obviously come to a relative consensus on the technology). Because Jumbo Frames aren't standardized, there can't be a standard for negotiating them. There's no "vendor" extension for negotiation because nobody has written and implemented one. –  Chris S Oct 2 '12 at 16:26

1 Answer 1

I found a partial answer through this answer:

http://www.chelsio.com/jumbo_enet_frames.html

However it is not entirely impartial as it is by a network gear manufacturer who tries to promote their network cards with tcp offload engine. However, that is not without its problems either. And even if 9k is too much for some applications, that doesn't mean 1500 is large enough. So any additional/unbiased answers are still appreciated.

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