forcing full duplex in iftab file


Can anyone tell me the command to force 100mb full duplex.

I know the iftab file has to be edited, but then I'm stuck.


marc g


I had some trouble with Apple NICs not liking the commands that I normally use under FreeBSD. How you do it there is ifconfig ed0 x.x.x.x netmask x.x.x.x media 100baseTX mediaopt full-duplex. You can use the seeting
of your choice the options are visible with a ifconfig -a (I think I don't have a mac handy)

I'm not sure about this format in the iftab file. It will work in the rc files and / or from the command line.



the ifconfig syntax within os x v10.1.1 does not seem to like normal bsd actions - keeps reporting "Operation not supported" - an SIOCS... error

" ifconfig en0 inet netmask broadcast media 100baseTX mediaopt full-duplex up "

... does not work on mac os x v10.1.1

so, what you have said is not correct

does not work in /etc/iftab, either

if anyone knows how to make a mac os x v10.1.1 system hold an IP address (selecting the proper media would help - instead of the dreaded "autoselect..."

please post ideas - IF THEY HAVE BEEN TESTED... that is :-o



I want to know how to cause my mac to switch to Full-Duplex instead of Auto-negotiate...

I am having SLOWWWWWWW copy speeds between to macs with 100base t NIC's. I am using a Linksys Switch that is capable of 200mbps throughput. I use it because I am serving off of a Cable modem to both macs and I cannot do it any other way without purchasing another IP.... The downside is this Duplex mismatch issue which sucks....

So anyone else have any input on making the macs only Full Duplex instead of Auto....?

I have been doing extensive research on this issue and as I am a layman in regards to UNIX it is a hit & miss scenario for me...

Thanks in advance.


in the end, I just got the cisco guy to make my port 100 half, and it works really fast.

not quite the solution I know but it's working as fast as 100 full on any other machine


Unperson Spotter
for media and mediaopt is okay, but the drivers seem to drop them on the floor (media with operation not supported, mediaopt silently)

Bug submitted.