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No jumbo frames (MTU 9000) with new Core i5 iMac?

59310 Views 90 Replies Latest reply: Nov 16, 2010 6:20 AM by Pinthea RSS
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Pinthea Level 1 Level 1 (20 points)
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Nov 16, 2009 6:45 PM
Discovered today that my day-old iMac Core i5 is missing the option to set MTU to 9000 (to enable jumbo frames). When in my network settings I have only options "Standard (1500)" and "Custom" and when I choose "Custom" the entry field shows allowed values of 72 - 1500. If I try setting to 9000 then it gets set to 1500. I used to have a "Jumbo (9000)" option with my previous 24" iMac (C2D) which I sold a couple of weeks ago. So I know my network hardware supports it, and having it set to Jumbo is very helpful in getting increased network throughput to my NAS.

To confirm, yes -- I am trying to set this via Ethernet settings and not AirPort. This issue occurs in "Automatic" network location and in any new ones I set up (such as "Home"). Also applies to any new users I try to create as a troubleshooting aid. I have bounced the gigabit ethernet switch I am connected to, just in case... I have not yet tried reinstalling 10.6.2 from the disc that came with the machine since I just brought it home from the Apple Store today!

The other network options on the "Ethernet" tab are:

Configure: Manually
Speed: 1000baseT
Duplex: full-duplex, flow-control
MTU: Standard (1500) or Custom (my only 2 choices)

Can anyone confirm that MTU 9000 (Jumbo Frames) is or is not enable-able on your Core i5 or i7 iMac?

THANKS!

Message was edited by: Pinthea

Message was edited by: Pinthea
iMac 27" Core i5, Mac OS X (10.6.2)
  • rack0 tack0 Level 4 Level 4 (2,205 points)
    Currently Being Moderated
    Nov 17, 2009 12:45 PM (in response to Pinthea)
    I would ask Apple, you have 90 days support may as well use it. Other than that have you tried using the ifconfig command in terminal?

    from the manual page:-
    mtu n Set the maximum transmission unit of the interface to n, default
    is interface specific. The MTU is used to limit the size of
    packets that are transmitted on an interface. Not all interfaces
    support setting the MTU, and some interfaces have range restric-
    tions.
    iMac 20", Mac OS X (10.6.2)
  • rack0 tack0 Level 4 Level 4 (2,205 points)
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    Nov 17, 2009 2:57 PM (in response to Pinthea)
    I have just tried it on my iMac 7,1 machine. It lets the custom be set from 72 to 9000 and checking in ifconfig confirms that its 9000. However the UI keeps displaying Standard 1500, not sure what is happening there, presume that is a UI bug.
    I normally run with an MTU 1492 and if I set it to this the UI does display Custom 1492.

    The ifconfig always seems to show the value that I set it to even when set from the UI.

    I am running 10.6.2 , I presume if its a new machine yours is also 10.6.x

    Hope you get the conformation that you can run 9000

    regards
    iMac 20", Mac OS X (10.6.2)
  • Scorpie Calculating status...
    Currently Being Moderated
    Nov 17, 2009 4:12 PM (in response to Pinthea)
    ifconfig is a privileged command, and if you already knew that, my apologies.

    Have you tried invoking the command using "sudo"? That lets you run the command as root. I don't have my Mac with me here at work, but I would give that a try:

    sudo ifconfig en0 mtu 9000

    It'll prompt you for your password.
    20" iMac (mid 2007) 2.4GHz 4 GB, Mac OS X (10.6.2)
  • Scorpie Level 1 Level 1 (130 points)
    Currently Being Moderated
    Nov 17, 2009 5:07 PM (in response to Pinthea)
    Ah, looks like you'll need to get the answer from the horse's mouth. The kernel must not understand that big value.
    20" iMac (mid 2007) 2.4GHz 4 GB, Mac OS X (10.6.2)
  • StephenCCH Level 1 Level 1 (45 points)
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    Nov 17, 2009 6:18 PM (in response to Pinthea)
    One question I have is: Were you running Leopard or Snow Leopard on your previously owned iMac?
    MacBook Pro 15-inch 2.2Ghz SR / iMac G5 (iSight) 2.1Ghz, Mac OS X (10.5.8), iMac G3 500Mhz 10.4.11 / iPod 3G 20GB / 5G 80GB
  • StephenCCH Level 1 Level 1 (45 points)
    Currently Being Moderated
    Nov 17, 2009 7:32 PM (in response to Pinthea)
    There was only one model of the 24-inch iMac that ever used the Nvidia 9400m graphics and that was the $1499 US priced Early 2009 model.

    All iMacs since 2006 (Intel) has had support for jumbo frames. On Apple's current online web site only the Mac Pro out of all current Macs has Jumbo frames specifically stated in the Tech Specs.

    I am going to check the developers section for Hardware specs and see if they have them up yet. This could answer this question very quickly.

    Message was edited by: StephenCCH
    MacBook Pro 15-inch 2.2Ghz SR / iMac G5 (iSight) 2.1Ghz, Mac OS X (10.5.6), iMac G3 500Mhz 10.4.11 / iPod 3G 20GB / 5G 80GB
  • StephenCCH Level 1 Level 1 (45 points)
    Currently Being Moderated
    Nov 17, 2009 8:11 PM (in response to Pinthea)
    Unfortunately nothing from the developer section. If I find anything about this though I will post here. Hopefully Apple can find out for you. If they do, please tell us as this would be a downgrade not an upgrade for the ethernet port.

    All other Macs seem to support Jumbo Frames according to the app Mactracker.
    MacBook Pro 15-inch 2.2Ghz SR / iMac G5 (iSight) 2.1Ghz, Mac OS X (10.5.6), iMac G3 500Mhz 10.4.11 / iPod 3G 20GB / 5G 80GB
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