Buffer Drops / QoS

Unanswered Question
May 7th, 2008
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Can anyone tell me what the buffer drops etc. tell me with this output? I see them climing, but is this excessive or normal?



#sh controllers ethernet-controller port-asic statistics

===========================================================================

Switch 1, PortASIC 0 Statistics

---------------------------------------------------------------------------

28383478 TxBufferFull Drop Count 0 Rx Fcs Error Frames

0 TxBufferFrameDesc BadCrc16 0 Rx Invalid Oversize Frames

0 TxBuffer Bandwidth Drop Cou 0 Rx Invalid Too Large Frames

0 TxQueue Bandwidth Drop Coun 0 Rx Invalid Too Large Frames

0 TxQueue Missed Drop Statist 0 Rx Invalid Too Small Frames

83659 RxBuffer Drop DestIndex Cou 0 Rx Too Old Frames

401841435 SneakQueue Drop Count 0 Tx Too Old Frames

0 Learning Queue Overflow Fra 0 System Fcs Error Frames

0 Learning Cam Skip Count


===========================================================================

Switch 1, PortASIC 1 Statistics

---------------------------------------------------------------------------

41143578 TxBufferFull Drop Count 0 Rx Fcs Error Frames

0 TxBufferFrameDesc BadCrc16 0 Rx Invalid Oversize Frames

0 TxBuffer Bandwidth Drop Cou 0 Rx Invalid Too Large Frames

0 TxQueue Bandwidth Drop Coun 0 Rx Invalid Too Large Frames

0 TxQueue Missed Drop Statist 0 Rx Invalid Too Small Frames

97312251 RxBuffer Drop DestIndex Cou 0 Rx Too Old Frames

2043119236 SneakQueue Drop Count 0 Tx Too Old Frames

8760 Learning Queue Overflow Fra 0 System Fcs Error Frames

0 Learning Cam Skip Count

******************************************************************


#sh controllers ethernet-controller port-asic statistics

===========================================================================

Switch 1, PortASIC 0 Statistics

---------------------------------------------------------------------------


28383478 TxBufferFull Drop Count 0 Rx Fcs Error Frames

0 TxBufferFrameDesc BadCrc16 0 Rx Invalid Oversize Frames

0 TxBuffer Bandwidth Drop Cou 0 Rx Invalid Too Large Frames

0 TxQueue Bandwidth Drop Coun 0 Rx Invalid Too Large Frames

0 TxQueue Missed Drop Statist 0 Rx Invalid Too Small Frames

83659 RxBuffer Drop DestIndex Cou 0 Rx Too Old Frames

401841435 SneakQueue Drop Count 0 Tx Too Old Frames

0 Learning Queue Overflow Fra 0 System Fcs Error Frames

0 Learning Cam Skip Count


===========================================================================

Switch 1, PortASIC 1 Statistics

---------------------------------------------------------------------------


41143578 TxBufferFull Drop Count 0 Rx Fcs Error Frames

0 TxBufferFrameDesc BadCrc16 0 Rx Invalid Oversize Frames

0 TxBuffer Bandwidth Drop Cou 0 Rx Invalid Too Large Frames

0 TxQueue Bandwidth Drop Coun 0 Rx Invalid Too Large Frames

0 TxQueue Missed Drop Statist 0 Rx Invalid Too Small Frames

97312547 RxBuffer Drop DestIndex Cou 0 Rx Too Old Frames

2043119236 SneakQueue Drop Count 0 Tx Too Old Frames

8760 Learning Queue Overflow Fra 0 System Fcs Error Frames

0 Learning Cam Skip Count

============================


Thanks!

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Joseph W. Doherty Thu, 05/08/2008 - 04:55
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Assuming these buffer drops indicate transmission queue drops, then it tells us from time-to-time the output port is being overdriven. Whether this is bad, and how bad, is both dependent on how often it is happening and the kind of traffic that it is happening to. TCP adapts its transmission rate to drops, so usually if they don't average more than about 1%, it's not a problem. Non-TCP traffic can be very sensitive to drops (and also queuing delays before the drops) but how much so is very variable; depends on the application.

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