10/100/1000

[bkaren1278]

I noticed something interesting yesterday and am hoping someone can explain it. When plugging in servers that were hard coded to 100 on gigabit ports the server performance choked. Shouldnt the IOS autonegotiate and provide std 100 service to the server? After switching the server nic to auto it immediately boosted to gigabit and all performance issues were solved.

does this make sense?It previously functioned at 100 very well for a long time.

[spremkumar]

Hi

Can you revert back about the other side port details where your server is getting connected ??

in some of the SFPs you wont be able to reduce the speed on the port its 1000 by default and the only option available..

regds

[bkaren1278]

the server support gigabit and the goal is to simply change them to gigabit.

I'm just curious how keeping the server at 100 actually degrades its performance on a gigabit switch. You would think it would function as normal and auto negotiate down to 100 seemlessly on the switch.

[glen.grant]

By doing what you did you created a duplex mismatch.The switch is set as auto unless you set the server as auto it "cannot" autonegotiate the speed and duplex . The switch can sense the speed correctly but cannot sense the duplex unless the other side is auto so it will default to half duplex , so you then have your server hardcoded to 100/full and the switch running 100/half with a collision domain activated. So you have a duplex mismatch which causes all kinds of errors and slow response , retransmissions etc....

You must match both sides on the coding , if the server is hardcode then the switchport must be hardcoded , if its auto then the switchport must be auto also.

[bkaren1278]

Thanks, this makes sense. The only question i have is how come the IOS didnt show me duplex errors?

[glen.grant]

I bet if you did a show interface you would see all kinds of errors on that link.

[Richard Burts]

Brook

The IOS did not show you a duplex mismatch because the IOS did not know that there was a mismatch. It could not detect the server duplex setting during negotiation because there was no negotiation when the server is hard coded. And while CDP is able to report duplex settings between Cisco devices, there is not anything to report duplex settings between the Cisco and the server.

HTH

Rick