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IPP LLC freelistBelowHiPriorityThreshold interrupt

Endorsed Question
Oct 11th, 2013
User Badges:

I have 2 4900M with Catalyst 4500 L3 Switch Software (cat4500e-IPBASEK9-M), Version 12.2(53)SG8 and i'm getting sveral messages like:


%C4K_SWITCHINGENGINEMAN-4-IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD: (Suppressed 237 times)IPP LLC freelistBelowHiPriorityThreshold interrupt


Does any one know what can be causing this?


Thank you.

Cisco Endorsed by Rakhshanda Khan
Arumugam Muthaiah about 3 years 10 months ago

Hi IFAP,


%C4K_SWITCHINGENGINEMAN-4-IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD:  (Suppressed 237 times)IPP LLC freelistBelowHiPriorityThreshold  interrupt


This error message indicates that available packet buffers have briefly dropped below the control packet threshold and hence only control packets are processed. There are no packet buffers available to process incoming data packets. This is most likely a temporary condition caused by transmit queue congestion on one or more ports that are buffering large numbers of packets.


IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD is an interrupt, which is always raised when packet buffer's (PB) cell count drops below this threshold (2048 cells). Once PB cell count below that threshold, only control and high priority packets are accepted by the switch. All other packets are dropped and Rx-No-Pkt-Buff counter would increment on corresponding interface.


Rx-No-Pkt-Buff indicates two possible issues:


1) stub getting oversubscribed. This is what we refer to the Stub Rx FIFO drops. These drops will not print the IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD message.

2) global packet memory temporarily unavailable.


The only possible known issue on the switch was an interface that is being used as mirror port and it's been at a 97% utilization constantly since about a week ago.


Suggestion:

  • This is an informative message, no further actions are necessary.
  • Clear the counters and check for any increase in output drops in any of the interfaces so that we can identify the interface where we see bursty traffic.
  • If the output drops are not increasing then these messages can be considered informational only.
  • If you see this error message continuously, please capture the below commands, and check Rx-No-Pkt-Buff counter is incrementing


#show interface counters detail


Switch# show interface gi3/6 counters detail

Port         InBytes      InUcastPkts    InMcastPkts     InBcastPkts

....

Gi3/6         0                 0            0                 1

Port        InPkts 512-1023  OutPkts 512-1023

Gi3/6              0                 0

.....

Port   Tx-Drops-Queue-1  Tx-Drops-Queue-2 Tx-Drops-Queue-3  Tx-Drops-Queue-4

Gi3/6           0                 0                0                 0

Port   Tx-Drops-Queue-5  Tx-Drops-Queue-6 Tx-Drops-Queue-7  Tx-Drops-Queue-8

Gi3/6           0                 0                0                 0

Port   Rx-No-Pkt-Buff     RxPauseFrames    TxPauseFrames   PauseFramesDrop

Gi3/6     785833                 0                0                 0


When global packet memory is used up one will see the IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD message. Instantaneous free list can be checked using below command,

#show platform hardware interface all | inc FreeListCount


To check whether packet drops are due to packet buffer full, use:

#show platform hardware interface stat | include NoPacketBuffAvailCount


If the above output shows a non-zero value or continuously incrementing value, then the system packet buffer is full and packets are dropped at the ingress. Then we need to reduce the queue size to fix this issue.


Regards,

Aru


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Arumugam Muthaiah Fri, 10/11/2013 - 05:55
User Badges:
  • Cisco Employee,

Hi IFAP,


%C4K_SWITCHINGENGINEMAN-4-IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD:  (Suppressed 237 times)IPP LLC freelistBelowHiPriorityThreshold  interrupt


This error message indicates that available packet buffers have briefly dropped below the control packet threshold and hence only control packets are processed. There are no packet buffers available to process incoming data packets. This is most likely a temporary condition caused by transmit queue congestion on one or more ports that are buffering large numbers of packets.


IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD is an interrupt, which is always raised when packet buffer's (PB) cell count drops below this threshold (2048 cells). Once PB cell count below that threshold, only control and high priority packets are accepted by the switch. All other packets are dropped and Rx-No-Pkt-Buff counter would increment on corresponding interface.


Rx-No-Pkt-Buff indicates two possible issues:


1) stub getting oversubscribed. This is what we refer to the Stub Rx FIFO drops. These drops will not print the IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD message.

2) global packet memory temporarily unavailable.


The only possible known issue on the switch was an interface that is being used as mirror port and it's been at a 97% utilization constantly since about a week ago.


Suggestion:

  • This is an informative message, no further actions are necessary.
  • Clear the counters and check for any increase in output drops in any of the interfaces so that we can identify the interface where we see bursty traffic.
  • If the output drops are not increasing then these messages can be considered informational only.
  • If you see this error message continuously, please capture the below commands, and check Rx-No-Pkt-Buff counter is incrementing


#show interface counters detail


Switch# show interface gi3/6 counters detail

Port         InBytes      InUcastPkts    InMcastPkts     InBcastPkts

....

Gi3/6         0                 0            0                 1

Port        InPkts 512-1023  OutPkts 512-1023

Gi3/6              0                 0

.....

Port   Tx-Drops-Queue-1  Tx-Drops-Queue-2 Tx-Drops-Queue-3  Tx-Drops-Queue-4

Gi3/6           0                 0                0                 0

Port   Tx-Drops-Queue-5  Tx-Drops-Queue-6 Tx-Drops-Queue-7  Tx-Drops-Queue-8

Gi3/6           0                 0                0                 0

Port   Rx-No-Pkt-Buff     RxPauseFrames    TxPauseFrames   PauseFramesDrop

Gi3/6     785833                 0                0                 0


When global packet memory is used up one will see the IPPLLCINTERRUPTFREELISTBELOWHIPRIORITYTHRESHOLD message. Instantaneous free list can be checked using below command,

#show platform hardware interface all | inc FreeListCount


To check whether packet drops are due to packet buffer full, use:

#show platform hardware interface stat | include NoPacketBuffAvailCount


If the above output shows a non-zero value or continuously incrementing value, then the system packet buffer is full and packets are dropped at the ingress. Then we need to reduce the queue size to fix this issue.


Regards,

Aru


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Aleksandr Yun Fri, 01/23/2015 - 08:14
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Good day.

I have the same problem.

 

Can anybody help me, how to show size of system packet buffer, and how I can reduce the size of buffer?

 

Thank you

Rakhshanda Khan Sat, 09/05/2015 - 00:09
User Badges:
  • Cisco Employee,

the show buffers command on Cisco 4500:

The interface buffer pools are used by the interfaces for input/output (I/O). When there are no more buffers in the interface buffer free list, the router goes to the public buffer pools as a fallback. There is no performance hit for a fallback.

Caching is a software manipulation that speeds up the availability of buffers for interrupt level driver code by bypassing some overhead.

Note: Normally, interface buffers should not be tuned.

 

Please refer to below document for buffer tuning:

http://www.cisco.com/c/en/us/support/docs/routers/10000-series-routers/15091-buffertuning.html#buffer_tuning

HTH

Rakhshanda Khan

luyenntk50db Mon, 06/29/2015 - 01:32
User Badges:

I have the same problem.

Pls guide me to config queue-limit  in 4900M switch.

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