[clue-tech] making ethernet autonegotiation not work

[Ken MacFerrin]

Jim Ockers wrote:
> Hi,
> 
> How can we break autonegotiation for ethernet link speed & duplex
> with a minimum of expense & effort?
> 
> So we have some nice ethernet equipment (NICs, switches) which
> supports 10/100 BaseT half and full duplex, and will happily
> autonegotiate to the best mode that both link partners support.
> 
> http://en.wikipedia.org/wiki/Autonegotiation
> 
> For operational reasons we need to make sure that 100BaseT never
> gets negotiated.  We have configured all link partners (software
> device driver config) to negotiate only 10BaseT and tried to
> disable autonegotiation in software, but since the (unmanaged) 
> ethernet switch supports 100BaseT (and will autonegotiate it if 
> asked) occasionally the link goes to 100BaseT.
> 
> Don't ask why, just trust me on this, we HAVE TO GUARANTEE THAT
> IT WILL ONLY EVER BE 10BASET.  It has to do with the fact that the
> cabling and connectors are NOT CAT5 nor are they intended for
> ethernet.  Plus they're long.  It all seems to work OK at 10BaseT 
> but not 100BaseT.
> 
> The unmanaged switch is $50 and the managed switch is $500.  Of
> course we can make the managed switch set its ports to only 10BaseT.
> Not so easy with the unmanaged switch.
> 
> I was hoping we could put a "high pass filter" or something made
> out of cheap analog components in line with the cable which would
> make the autonegotiation pulses not work.  A hardware solution seems
> like the best idea.
> 

Well.. if you "have to guarantee" it, then I'd still say a managed
switch is the way to go.  If you don't need gigabit then there's no
reason you'd need to spend $500 these days.  A quick search at Newegg
will give you options in the low 100's and will save you the time of
experimenting with filters and such.

http://www.newegg.com/Product/Product.aspx?Item=N82E16833156060

-Ken