ACE duplicate ack and tcp out-of-order errors

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Apr 7th, 2010
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I have just performed a capture using a NAM in my 6500 on the port attached to my ACE appliance.

What i have noticed in the capture is a lot of duplicate ack errors and tcp out-of-sync errors.

The reason we found this was becuase the link utilisation per session seems higher than we expected, hence are the errors adding to this and is there any way to remedy them?



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scott-goodwin Thu, 04/08/2010 - 04:10
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Another thing to add, we have tried doing this from a single request and get the same result, hence i cant see this being congestion

which you would expect to generate the duplicate ACK.

Any ideas??


Sean Merrow Thu, 04/08/2010 - 11:49
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Hi Scott,

I'm not sure why you would see duplicate packets, although when you use SPAN, I know you can see them when you configure it to capture both directions on a VLAN.  This is because you see each packet as it enters and leaves the VLAN.  I don't know if that would apply to a NAM.

One thing you could do is use the ACE 4710's built-in capture utility to see if you see the same symptoms from an alternative source.  This is covered in the Capturing Packet Information section of the configuration guides.

Hope this helps,



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