[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.


This doesn't answer your hardware question, but assuming these are linux
boxes, have you tried forcing the speed and duplex using mii-tool?

# mii-tool --force=10baseT-HD eth0

-Ken