Airport Utility on iMac with Jumbo Frames can't read Airport configuration

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Level 1

1 points

Airport Utility on iMac with Jumbo Frames can't read Airport configuration

My 24" iMac is connected to a Netgear switch (GS608 rev2) that supports Ethernet jumbo frames. My GigE Airport Extreme base station is also connected to the Netgear switch and is acting as a gateway for my cable modem connection. Here's the rough wired layout:

iMac--Netgear--Airport--Cable Modem

The iMac has jumbo frames enabled (MTU=9000) and can communicate fine to the Internet and other devices on my local LAN (including a Netgear NAS box also with Jumbo frames enabled).

Airport Utility on the iMac starts and discovers my 3 Airports (1 extreme + 2 express) but if I double click on one of them to configure it, the window says "Reading the AirPort Extreme configuration..." and hangs there never bringing up the setup screen. Printer jobs to the shared USB printer that worked before Jumbo Frames were enabled on the iMac are also failing. The same happens for the 2 Airport Express as well although I can still steam Airtunes music to them.

Any ideas what might be wrong ? Do the airports have problems negotiating with jumbo frame enabled Macs ?

My wireless MBA with std MTU can still communicate fine with the Airports.

Thanks,
E

Message was edited by: Gaijin Kuma

2007 24" iMac / 2nd gen MacBook Air, Mac OS X (10.5.6)

Posted on Feb 26, 2009 5:36 PM

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Answer 1

Cadre

Level 2

174 points

Mar 10, 2009 8:04 PM in response to Gaijin Kuma

None of Apple's Airports support jumbo frames.

The networking chip that Apple uses in the Airport Extreme has the capability to support jumbo frames, but it isn't an option that Apple has chosen to expose to the user. So you can't reliably use the Airports on a jumbo frame enabled subnet.

The likely reason the Internet is still working is that, unless your uploading, it's unlikely the iMac sent a packet in excess of 1500 bytes to the Airport. The Airport is always sending 1500 byte packets which your iMac wold receive fine regardless of what the MTU was set (well, unless it was set below 1500).

Some people do report success but I would be wary of their results, they may not have down/upped the interface so the MTU may have been listed as changed, but not yet actually changed to the larger MTU. No-one has actually posted a tcpdump -e capture showing an Airport actually sending/receiving packets in excess of 1500 bytes.

Some more links to this discussion topic-

http://discussions.apple.com/thread.jspa?threadID=1085469
http://discussions.apple.com/thread.jspa?threadID=1222397
http://www.smallnetbuilder.com/content/view/30188/96/

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Answer 2

Gaijin Kuma Author

Level 1

1 points

May 13, 2009 10:19 AM in response to Gaijin Kuma

I am happy to report that the 10.5.7 update has resolved the issues. My iMac with jumbo frames enabled can now properly printer to USB printers attached to the Airport Extreme and Airport Utility can read its configuration.

Thanks Apple!

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Answer 3

fafhrd1

Level 1

0 points

Jul 17, 2009 8:39 PM in response to Cadre

I recently added a Buffalo NAS to my network, set jumbo frames on my Mac Mini and MacBook Pro but noticed that I was not getting the throughput that I thought I should be so I did a tcpdump and found that I was only getting 1500. I move the Buffalo NAS to the DGS-2208 DLink Gig switch, did another tcpdump and now I am getting an MTU of 9000. Would seem to indicate that the AEBS is NOT capable of jumbo frames.

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