Unanswered Question
Nov 29th, 2007
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I have a two interfaces, one fiber on a 720 and one on a 48port gig card in a 6500, and a port-channel interface counting a huge number of OutDiscards...

Any idea what can cause this?

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Edison Ortiz Sun, 12/02/2007 - 16:06
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It could be oversubscription. What type of line card are you using ?

william.briere Tue, 12/04/2007 - 09:22
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Here is the model of the card and sup...

WS-X6748-GE-TX (In slot 1 on a 6506E)

WS-SUP720-3B (In slot 5 on a 6506E)

I guess oversubscription would surprise me because we don't really have anything connected yet that can push a lot of data. How much network traffic is generated by using GLBP and VTP?

I have attached a doc of how things are connected...

Edison Ortiz Tue, 12/04/2007 - 09:28
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WS-X6748-GE-TX are 1.2:1 oversubscribed and each switchport has a 1Mb buffer.

Are the outdiscards incrementing ? How much traffic is being sent via this links ?

william.briere Tue, 12/04/2007 - 09:33
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I will need to take some time to gather that info...

Is there any tuning I can do in the event it is oversubscription?

There really isn't any traffic of any significance of other than the VTP information and the GLBP activity...

Can a misconfigured portchannel cause this?

william.briere Tue, 12/04/2007 - 09:42
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The second port on the sup 720 3b, which I changed the media-type to sfp, was also counting OutDiscards...

Other than what you see in the diagram that is all that is connected at the present time. The ports are all trunked using dot1q

Edison Ortiz Tue, 12/04/2007 - 09:45
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Oversubscription is a hardware limitation. Seeing the port counters should help us identify if you have this condition. Also, try clearing the counters and see if they are increasing.

What's the value on input/output rate ?

Clear counter errors and then see what the utilization is on the port when you are seeing the OutDiscards. There are a number of things that can cause the OutDiscards but most of them are tied to port utilization. We had that issue when spanning a port for sniffing when the port the sniffer was attached to was set to portfast. More info on the topo would be helpful.


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