2 Replies Latest reply: Sep 23, 2012 10:08 AM by MarcusV24
MarcusV24 Level 1 (0 points)

Why is it not possible to change MTU size to more than 1500? Buying such a high quality product, I would expect that it supports jumbo frames!


My NAS supports jumbo frames, the Air Port Extreme does but a brand new iMac doesn't???



Is there any patch or somethin to fix this?



iMac, OS X Mountain Lion (10.8.2)
  • BDAqua Level 10 (122,276 points)

    Hi Marcus,


    I find conflicting info on this...

    The Ethernet port supports the configuration of Ethernet frames larger than 1,500 MTU (Maximum Transmission Unit).


    Can anyone confirm if the new 2011 imacs already support jumbo frames? I heard it now uses a new broadcom ethernet chip that now supports jumbo frames on the 21 inch model. They removed jumbo frames support in the previous i5 and i7 models...


    Hmm, I remember that the iFix tear down revealed that the 2011 iMacs had a Broadcom BCM57765B0KMLG Eithernet chip. (just go to the page and if you are using safari/firefox press command + F and type "Broadcom" to jump to that particular)




    so I did a little googling and found out that:






    Integrated 10/100/1000BASE-T transceiver with:
    - 10/100/1000BASE-T triple-speed MAC
    - Compliant with IEEE standards
    - Compliant with IEEE 802.3az draft standard for Energy Efficient Ethernet™ (EEE)
    - State-of-the-art physical layer interface that exceeds IEEE requirements
    - Jumbo frame support with up to 9.6 KB frame size
    - EthernetAV protocols with IEEE 802.1AS, 1588-2008, IEEE P802.1Qat and IEEE P802.1Qav support


    So it should support Jumbo Frames.

    http://www.philmug.ph/forum/f23/new-imac-early-2011-sandy-bridge-processors-7106 4/index8.html


    Originally Posted by mpe View Post


    At least mine doesn't

    Weird. My 27" 3.1GHz iMac that was delivered yesterday supports jumbo frames fine. I was quite concerned that it wouldn't because I rely on them for good performance with my NAS


    I set it using System Preferences -> Ethernet -> Advanced -> Ethernet -> Configure Manually.

    I've confirmed the setting by checking the output of ifconfig. It shows an mtu value of 9000.



    Some of the 2010 iMacs did not I read.

  • MarcusV24 Level 1 (0 points)

    Hi BDAqua!


    Thanks for your fast and detailled reply!


    I'm sorry, I expressed myself not clearly - I was talking about the WiFi Interface, not the LAN Interface.


    LAN Interface does support Jumbo Frames, but the W-LAN doesn't.