adding 1G ethernet to a 100M network

[James Knott]

CLIFFORD ILKAY wrote:
> 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.
Regardless, that should only affect the one port, not the entire switch.

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