jumbo frames: what the?

skanky

skanky

skanky

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running a gigbit lan with a dell 24 port switch and the required cat5e, never really looked into jumbo frames before but i feel i really should.

i have these devices and also the available options i get when looking at "jumbo packets" in the respective properties for the LAN card, all the devices are gigabit capable of course.

laptop #1 (Intel Pro 1000PL) = 4088, 9014
laptop #2 (Intel 82577LM) = 4088
nas #1 (qnap 419p) = 1500, 4074, 7418, 9000
nas #2 (qnap 409) = 1500, 4074, 7418, 9000
gaming rig (realtek PCIe GBE Family Controller) = 2KB, 3KB, 4KB, 5KB, 6KB, 7KB

how do i make heads or tails of those? i remember trying it once ages ago, not sure what i was doing and was unable to access the nas for some reason after changing a jumbo frame settings so obviously don't want a repeat of that!

both the nas devices are set to 1500 as there is no "off" option on them, however all the machines are currently set to "disabled"
 
Jumbo frames should give you faster transfer speeds in theory because it reduces overheads, but you may run into compatibility issues.

I've not really experimented with them myself however, so with any luck I'm sure someone else will come along and explain the compatibility issues better than I can. :)

This is worth a read however: http://en.wikipedia.org/wiki/Jumbo_frame

It seems that 1500 bytes is the standard frame size, so I guess anything larger is considered jumbo!
 
Used to be 9000 when I used to work configuring servers about 4 years ago in Swindon. Just means you get a bigger PDU if i understood it correct. TCP/IP overhead stays the same.
 
I've got mine on 4k which increased the speed a bit when transferring to my Synology NAS.
 
should i change them to these values, as they are kind of similar, in a weird "they're all 4000" kind of way..

laptop #1 (Intel Pro 1000PL) = 4088, 9014
laptop #2 (Intel 82577LM) = 4088
nas #1 (qnap 419p) = 1500, 4074, 7418, 9000
nas #2 (qnap 409) = 1500, 4074, 7418, 9000
gaming rig (realtek PCIe GBE Family Controller) = 2KB, 3KB, 4KB, 5KB, 6KB, 7KB

also what happens to machines with non-gigabit connections (xbox360, old laptop, iphone etc), will it affect those devices?
 
I'd just set them to the highest value, MTU on the ports will do the fragementation dis/re-assembly. Check out PMTU.
 
I did some experimenting (and was expecting it not to work!) and set all my PCs & switches to the maximum value for each (IIRC they're a mixture of 9000, 9K, 9014). All works fine, and the jumbo framed PCs can still print to the 10/100 printer fine.
 
its not liking it, hell, its not even liking all the 4K values.

i can set the NAS devices to 4K but if i set the machines to the similar value, i cant browse shares, i cant even map to the web interface :/ it only works when i set the machines to "disabled"
 
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Check your Dell Switch actually supports them. Some models, like the 2708, don't.

In my experience it's not a big deal, even with 9k frames its only worth a couple of MB/s at best.
 
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Check it supports jumbo frames, check the link speeds etc and then also check MTU settings on the ports (if it has any). If you can, get a wireshark capture and see what you are getting back ICMP wise.
 
its one of those unmanaged 24 port switches, dont think i can check any of those settings, cant remember the model number off hand but its rack mountable (1U maybe?) and quite noisy :)
 
Have a look on the switch see if you can find a model, then do a search on dell.com to get the spec and see if it supports Jumbo frames. Also, might be a silly question - but is the switch definitely gigabit?
 
My very extensive testing a couple of years ago with high end gear suggested that actually it's generally not worth it except for *very* specific scenarios with a single traffic type. I was surprised at the time but the methodology of the testing was sound and the results were consistent. Obviously core links get high MTU to allow for encapsulation but we never hard code endpoints unless customers request it, in which case they're on their own.
 
To use jumbo frames, every device that the packet travels through needs to have jumbo frames enabled etc..

If its not working, then something somewhere isnt enabled or doesnt support it.
 
SMN said:
Have a look on the switch see if you can find a model, then do a search on dell.com to get the spec and see if it supports Jumbo frames. Also, might be a silly question - but is the switch definitely gigabit?
Click to expand...

its the powerconnect 2724 and yes its definately gigabit! :)
 
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