Tell Me All You Know About Gigabit Jumbo Frames

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BuGaLoU

[H]ard|Gawd
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Apr 24, 2002
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It is disappointing such little info on gigabit Ethernet jumbo frames exists on the internet. All I can find is spec stuff, and implementing it in a large enterprise environment. Basically I have issues with just using it in a soho environment.

I have NICs capable of jumbo frames and a SMC switch capable of jumbo frames. I am able to turn it on with the NICs but it causes the network connection to become unstable and it disconnects a lot. I have it tied into a standard 10/100 switch via a crossover cable. To use jumbo frames does every device on the network have to be compatible or will it auto sense? Do I have to configure things locally more than just enabling jumbo frames on the NIC settings?

Anything you might know about this would be helpful in trouble shooting my issues.
 
Everything needs to be jumbo frame capable. The 10/100 device is causing the problems in this case. It's recommended to use a layer 3 switch to switch between 10/100/1000NJ(non-jumbo) and 1000 jumbo.

One cheap way to get around the problem is to use a machine as a router, put a jumbo capable gbit nic card in it, hook it to the smc. Put another 100MBit card in there, and hook it to the other switch. The machine would then take care of breaking the jumbo packets apart for the 10/100 devices.
 
sandmanx said:
Everything needs to be jumbo frame capable. The 10/100 device is causing the problems in this case. It's recommended to use a layer 3 switch to switch between 10/100/1000NJ(non-jumbo) and 1000 jumbo.

One cheap way to get around the problem is to use a machine as a router, put a jumbo capable gbit nic card in it, hook it to the smc. Put another 100MBit card in there, and hook it to the other switch. The machine would then take care of breaking the jumbo packets apart for the 10/100 devices.
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Great suggestion. I could use my server (Win2k AS) is there any configuration I would need to do in the routing settings?
 
BuGaLoU said:
Great suggestion. I could use my server (Win2k AS) is there any configuration I would need to do in the routing settings?
Click to expand...

I don't think there would be anything special. It may take a good chunk of processing time to actually do the routing though. I've never tried it myself, but I was wondering how well it would work. Of course, a little extra time on the 10/100 isn't a big deal, since those devices don't have a gigE card, they aren't extremely time sensitive most likely.
 
Ok, I did all this and had a gigabit only segment, but file sharing will not work and the terminal service to my server freezes constantly. File sharing will not list any files or folders. Do I have to manually adjust the MTU or something.
 
BuGaLoU said:
Ok, I did all this and had a gigabit only segment, but file sharing will not work and the terminal service to my server freezes constantly. File sharing will not list any files or folders. Do I have to manually adjust the MTU or something.
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Make sure you have the same size packets on all interfaces. The max MTU on the SMC is 9000, so make sure all the others are set the same.
 
sandmanx said:
Make sure you have the same size packets on all interfaces. The max MTU on the SMC is 9000, so make sure all the others are set the same.
Click to expand...

How do I set the MTU in a windows environment? I know there is a registry hack way, but it thier a program or setting I am just over looking that woul dmake it easier?
 
BuGaLoU said:
How do I set the MTU in a windows environment? I know there is a registry hack way, but it thier a program or setting I am just over looking that woul dmake it easier?
Click to expand...
I think you can using netsh, but that might only be with ipv6.
 
BuGaLoU said:
How do I set the MTU in a windows environment? I know there is a registry hack way, but it thier a program or setting I am just over looking that woul dmake it easier?
Click to expand...

Go to device manager and look under the properties of your card. There should be a value to set the size of the jumbo frames. On my Intel cards, there is a dropdown box and preset sizes. For the ones onboard an Asus A7N8X-E Deluze board there is a value you can set manually.
 
sandmanx said:
Make sure you have the same size packets on all interfaces. The max MTU on the SMC is 9000, so make sure all the others are set the same.
Click to expand...

Is 9000 the max size or only size for the SMC switch?

The reason I ask is that the device I use states:

"When using Jumbo Frame, the switch must support the Jumbo Frame standard designated (4100bytes/7418 bytes)"


Will this work with the SMC switch or am I out of luck and must have something that supports 9000? I checked SMC's website but the info I could find had no details on how it handles Jumbo Frames.
 
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