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Cisco Bug: CSCtc15675 - Packet stuck in PXF queue upon RF channel del/add for WB interface

Last Modified

Jan 31, 2017

Products (1)

  • Cisco uBR10000 Series Universal Broadband Routers

Known Affected Releases


Description (partial)

 If the last RF channel in a Wideband interface in DBS mode is removed and then
a channel is added back to the same WB interface while there are untransmitted
packets still sitting in any of the packet queues on that interface, the WB
interface may be wedged, i.e., packets can no longer be transmitted on that WB
interface. This trigger condition may happen when the channel removal and
addition happen very rapidly under traffic through that WB interface (such as
when changing rf-channel by pasting in a new configuration). It may also happen
when the WB interface is being flow controlled or back throttled by OCQ, while
the RF channel is unconfigured and then configured again inside the controller.
To see if a packet queues on a WB interface are stuck, issue the command "show
pxf cpu queue wideband 1/0/0:0" (substitute with the proper interface name) a
few times. If the queue "Len" field is not zero, but the "Dequeues" count does
not increase for any queue, that queue is stuck. In this case, further do "show
pxf cpu stat queue | i Flowoff|OCQ" multiple times. If the flowoff and OCQ
counters do not increase, it is a confirmation that the queues are stuck

In the example below QID 351397 is stuck full and is not dequeuing any packets.

ubr10k#show pxf cpu queue wi1/0/0:5

Cable Interface Queues:
QID     Len/Max  Dequeues   TailDrops   MinRt  Wt/Quantum  ShapeRt FlowId
                                        (Kbps)             (Kbps)
131093    0/255  0          0           0         1/240    0       31    
131094    0/255  0          0           0         1/10000  0       32797 

Cable Service Flow Queues:
* Best Effort Queues
QID     Len/Max  Dequeues   TailDrops   MinRt  Wt/Quantum  ShapeRt FlowId
                                        (Kbps)             (Kbps)
346016    0/255  0          0           0         1/240    10000   327573
343081   18/255  0          0           0         1/480    33000   102085
351397  255/255  0          348         0         1/480    33000   102086
351235    7/255  0          0           0         1/480    33000   102087

This problem is seen in the field in two cases: 
1) When there is rapid unconfiguration and then configuration of the RF channel frequency at the controller level, when those channels are actively transmitting packets. 
2) When modifying the rf-channel configuration on a wideband bonding group
quickly by pasting in configuration that adds and removes the channels while
traffic is flowing.
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