Ethernet autonegotiate vs forcing full speed

Lennart Sorensen lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org
Fri May 25 15:22:49 UTC 2007


On Fri, May 25, 2007 at 11:06:42AM -0400, Neil Watson wrote:
> There is debate at work regarding network Ethernet auto-negotiation.
> I'm the newcomer.  Historically they say they had problems with auto-neg
> and their cisco gear (catalist) and now manually set all switch ports
> and server NICs to full/full.   I've never heard of such a policy.  It
> seems to make extra work for all parties since all gear defaults to
> auto/auto.  Additionally, I spent some time trouble shooting a Linux
> server that I had newly configured for bonding.  I could not force the
> NICs to full/full.  When I had the cisco guy change the switch ports to
> auto/auto the bonding worked instantly.
> 
> Should this manual configuration of full/full be the exception or the
> rule?

I certainly always use auto negotiation.  Of course I wouldn't be
surprised if there was crappy equipment made early on that got the
negotiation wrong and screwed up as a result.  I would not expect
anything current to have any such problems though.  Maybe some people
had problems with their crappy old 10mbit stuff years ago and got a
policy that made sense 2 decades ago stuck in their heads as the only
way to do things.  Of course 100mbit could support auto negotiation, but
it wasn't mandetory to support it.  10mbit simply didn't have it
initially, and I don't know if any 10mbit ever did support
autonegotiate.  I know gigabit by spec MUST support auto negotiation.  I
wouldn't be surprised if the drivers for many gigabit ports may not even
support setting the port speed manually since there shouldn't normally
be a reason to want to do so.  Gigabit also doesn't use cross over
cables (or at least has no need for them), which makes life simpler.

--
Len Sorensen
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