Cisco 3750G stack and slow network troughput to certain NICs

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Jul 29th, 2009
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We have a stacked environment with 3 cisco 3750G switches.

We see that the network troughput is not getting its full potential, the highest load we see on a (1 gb) nic is 25%...

Also the line is not steady at 25% but its going down and up every second.

We tested with different network cards and settings.

What we could find is that a INTEL 1000 MT server nic is a lot faster then a onboard broadcom netextreme II nic.

We can get speeds of 105Gb/h and with the broadcom nics only 20GB/h ...

Have somebody heard of incompatibility issues with these switches and maybe can some sort of update of the switches can help?

We now run IOS 12.2-35-SE5 ....

Please share your thoughts...



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Joseph W. Doherty Wed, 07/29/2009 - 03:12
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I believe there have been several posts about throughput issues with 3750 switches (other forums). I found a bug, CSCeg29704 (fixed in your release, I believe), that described an issue with poor TCP performance caused by poor default egress settings when QoS enabled. Even with your release, I'm unsure default settings are ideal for all traffic types, with or w/o QoS enabled, since I also recall(?) another issue when ingress is gig and egress is 100.

What you might do is check whether there appears to be a high packet drop rate within the switch, and if so, you might try some manual tuning to see if that rate can be reduced. Your IOS is relatively recent, but you could also try a newer release.

compassnl Wed, 07/29/2009 - 03:23
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Hi thanks for you reply,

I would like to read something about others having the issue "since I also recall(?) another issue when ingress is gig and egress is 100. " as you described..

it indeed seams that we only have 100 mbit on the receiving end, but still its a 1000 mbit link.

I cannot find any packet drops on the switches or on client side whatsoever..


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