adding 1G ethernet to a 100M network

CLIFFORD ILKAY clifford_ilkay-biY6FKoJMRdBDgjK7y7TUQ at public.gmane.org
Thu Jul 29 19:08:12 UTC 2010


On 07/29/2010 02:57 PM, Lennart Sorensen wrote:
> On Thu, Jul 29, 2010 at 02:38:49PM -0400, CLIFFORD ILKAY wrote:
>> There is a caveat. At a colo facility recently, we installed a gigabit
>> D-Link switch figuring that it would "just work". The network
>> performance of any of the machines connected to that switch was abysmal
>> even though the colo facility had provided us with a 100Gbit/s
>> connection to their Cisco switch. Apparently, consumer grade switches
>> like the D-Link and others cannot auto-negotiate to the highest possible
>> rate if the other end isn't configured to auto-negotiate. The other end
>> was configured to be 100Gbit/s, full-duplex. The D-Link would fall back
>> to 10Mbit/s, half-duplex, thus explaining the poor network performance.
>> Replacing the D-Link with a Cisco (not Linksys) switch and setting it to
>> 100Mbit/s, full-duplex was the solution.
>
> 100Gbit/s?  I don't think I believe that.
>
> Now if one end doesn't autonegotiate, then you fall back to half duplex.
> You still get the speed right though, but because of colisions (or at
> least what the network port thinks are collisions) you get pretty bad
> performance.
>
> To me, it is very stupid of the colo facility to not use autonegotiation
> by default.  After all if you don't know to set your port to a fixed
> setting on your machine, you get the exact same problem.  It is really
> just plain dumb of them to do so.

By fixing the rate, they can differentiate between 10M, 100M, and 1000M 
service and charge accordingly. This episode explained why in another 
colo facility where we didn't have a switch between the server and the 
colo facility's switch, we had to use ethtool to set the rate or again, 
we'd fall back to 10M, half-duplex. That colo facility was never able to 
explain why and had just shrugged it off.
-- 
Regards,

Clifford Ilkay
Dinamis
1419-3266 Yonge St.
Toronto, ON
Canada  M4N 3P6

<http://dinamis.com>
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