Why does iMac (Mid 2012) not support Jumbo Frames?

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).

http://support.apple.com/kb/HT4619

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)

http://www.ifixit.com/Teardown/iMac-...eardown/5485/2

so I did a little googling and found out that:

http://www.broadcom.com/products/Eth...lient/BCM57765

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 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.

http://forums.macrumors.com/showthread.php?t=1148176

Some of the 2010 iMacs did not I read.