Fast card speed, slow connection!

[TechMonkey]

Had fun tracking down a network problem Friday. We have been having 'fun' with our Net connection after it was upgraded and the speeds haven't been spectacular. One thing we did notice though was originally we were speed testing on the NM's machine but I ran one on mine and it was noticably faster. After much tracking down and testing we found the only difference between our machines were the NMs was running 1000mb/s and mine was at 100mb/s. Mine should be running at 1000mb/s but being set to auto at both ends it defaults to 100. I have no problem with this if it means I am going to get faster speeds but don't understand why a faster connection speed causes a slower link.

 

Can any one shed any light?

[DMcCoy]

How long is the cable? Cat 5,5e,6? Any errors counts on the switch?

I just replaced some switches here and used the 1Gb uplinks until I remembered that the old switches that aren't fibre here were around 90m away with only cat 5 cable. I wondered why I was losing connection even with telnet to the switch!

[Geoff]

Sounds like cabling issues to me. Break out the testing gear.

[TechMonkey]

Well we are in the next room so it can't be that far, 10m wiould be an overestimate and when we force the NM's machine to run at 100 it runs as fast as mine!! All very confusing! Even more than why mine has decided to stick at 100 on exactly the same config! Networks gotta love em.

 

Ohh and the only network testing we have is a little 2 part box that says if the link works or not. Nowt fancy here

[john]

Is it the TCP Receive Window size I wonder? I use Dr TCP to adjust them and that works well for vaious home user ADSL problems.

[MrDarcy]

Hi. I'm a bit confused as to what you have connected these PCs to - does your switch support Gigabit? If so, why should two Gigabit network ports both set to Auto default to 100Mb? Check you cabling.*

 

Have you configured anything to a fixed speed? There is an oddity when you fix one end to 100Full-duplex and set the other to Auto: Auto responds to a fixed speed by matching the speed, but setting itself to Half-duplex, so ends up as 100Half-Duplex - a 'Duplex mis-match' with one talking and listening simultaneously, the other expecting to talk without interruption, then listen.

 

 

* Not using cable splitters are you?

 

 

Ed

[TechMonkey]

Hi. I'm a bit confused as to what you have connected these PCs to - does your switch support Gigabit? If so, why should two Gigabit network ports both set to Auto default to 100Mb? Check you cabling.*

 

Have you configured anything to a fixed speed? There is an oddity when you fix one end to 100Full-duplex and set the other to Auto: Auto responds to a fixed speed by matching the speed, but setting itself to Half-duplex, so ends up as 100Half-Duplex - a 'Duplex mis-match' with one talking and listening simultaneously, the other expecting to talk without interruption, then listen.

 

 

* Not using cable splitters are you?

 

 

Ed

 

Switch is gigabit. Both PC's are exactly (bought at the same time from the same batch) the same with gigabit cards. Both on Auto. Mine autos to 100, NM's autos to gigabit but the NM's seems to run slower.

[craiglay]

Not using a Realtek 8169 series NIC by any chance? And HP switches?

 

i'm having issues with using gigabit on this card on a network point that supports a Broadcom NetExtreme at gigabit, keeps defaulting to 100Mbit. Latest drivers make no difference. The Realtek will negotiate gigabit on a cheap 8 port Netgear switch though.

 

Any ideas?

 

Craig

[TechMonkey]

It is a Broadcom NetExtreme but as I said the 100mb/s isn't a problem at teh moment becuase that gives the faster link speed. Just a tad confusing

[craiglay]

Sorry, should have made it clearer, the Realtek is the one that wont do gigabit, the Broadcom does gigabit on the same cable.

 

Your situation maybe something to do with jumbo frames, RWIN, TCP offloading, could be anything really.

 

Craig