Re: turning off auto-negotiation on gigabit interface

"Trendkill" <jpmason@xxxxxxxxx> wrote in message
news:9032c092-d2b9-4dd9-aefd-b761c92482ce@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jan 27, 11:36 am, "noah davids" <nd...@xxxxxxx> wrote:
It is my understanding that the gigabit spec requires auto-negotiation,
so
what does turning it off really do?

--
Noah Davids
Serendipity is a function of bandwidth
E-mail: nd...@xxxxxxx
Web: http://members.cox.net/~ndav1

Well, technically auto-negotiation is only for slower than gig
settings, since a gigabit connection cannot be half-duplex.

negotiate is needed on 1000M to sort out the wiring, master / slave etc for
1000 Base-T. It doesnt set the speed (unless the other end is slower), but
it does set up the interface.

However,
and per Cisco Best Practices, either auto/auto or gig/gig is fine, so
long as you match on both sides. I have also noticed some NICs that
do not have a gig/full setting, and therefore you must go gig/gig. I
have also noticed other boxes that seem to have issues when
configuring auto on both ends. The bottom line is, match on both
sides, and look at vendor documentation to see what they recommend for
their specific device.

The above being said, I am not sure where you have seen that gig
requires auto negotiation, as that is not correct.

the reference comes from the IEEE standard - auto negotiation is a required
part of the standard for GigE 1000 Base-T, not just optional as it was with
100 Base-Tx.

remember that as part of setup on 1000 Base-T, the 2 ends negotiate to sort
out pairing etc, so this sort of makes sense.

as a practical issue, some devices REQUIRE a linked device to be using auto
at Gigabit, or they dont work, even with fibre ports.

For example, a recent wierdness trying to bring up fibre GigE links to a
Foundry MLX-4 turned out to be the SDH mux it was plugged into was set for
no negotiate, and the Foundry insists that auto is enabled.

the really annoying bit was that the MLX port had a "negotiate" option, but
the only allowed setting was "yes".

When we had a mismatch, the Foundry lit the green light against the
interface on the card, but no L3 traffic..... Serious head scratching until
we ignored the lights and went thru the logs.

i have other similar issues on GigE - so i suggest that if you have a GigE
or a 10/100/1000 device, you might need "auto".

Perhaps it is for
a specific server or hardware? Turning it off simply implies that the
speed and duplex is hard set, and is not negotiated on that side of
the configuration. Auto negotiation is required if the hardware/
server does not have gig/full as a set option, in which case both
sides would be configured to negotiate to the optimal setting.
--
Regards

stephen_hope@xxxxxxxxxxxx - replace xyz with ntl


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