Poor network performance: a lot of timeouts

Vinny Abello vinny at tellurian.com
Mon May 30 18:22:43 PDT 2005

At 04:56 PM 5/30/2005, Sebastian Ahndorf wrote:
>Kris Kennaway wrote:
>>>Both sides must have same config, autosense should work if there 
>>>is no config possibility in other end.
>>autosense may in fact not work, especially on low-quality NICs like rl.
>I don't agree to that.
>I had similar problems with my network using a cheap switch with 
>some realtek nics. I had the nics running 100baseTX Full Duplex.
>Changing this to autosense made the problems gone.
>Reason (as some people of the german questions-list told me):
>Many cheap switches always send their autosensepakets, and have 
>great problems if the nics connected to the switch do not response 
>to the autosensepakets (cause they are configured to 10/100baseTX 
>full/half duplex).
>Also realtek nics are far away from being good nics, they work 
>without problems with the autosensemode and a cheap switch for me 
>(and many other people I know).
>I would suggest the starter of this thread to use autosense with his 
>nic (if not tested yet).

The deal is simply this:

Autosense must be enabled on both sides to autonegotiate speed/duplex.

If you force one side to full duplex, the other side still autosenses 
(on most unmanaged switches), fail, and will fall back to half duplex 
causing a duplex mismatch. You have to force the other side to full 
duplex as well. If you cannot do this, leave it at auto, or set the 
side you can manage to half so they agree.

I personally like to leave everything on auto except links between 
switches and between routers and switches which I force to full. It 
always works out well for me on practically any platform or OS. Maybe 
on one or two occasions I've experienced faulty drivers which cause 
the autosensing to not work on the NIC and just default to half duplex.

Vinny Abello
Network Engineer
Server Management
vinny at tellurian.com
(973)300-9211 x 125
(973)940-6125 (Direct)
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