[nsp] Output drops

[Ariel Brunetto]

Hi All,

I have a Cisco 7206 with a POS interface with QoS. I noticed output packet
drops. I have one LLQ queue and Fair Queue for class-default. There is not
"no-buffer-drop" and the line rate was not reached in the output direction,
as you can see. There is not any kind of policer (rate-limit/MQC police) or
traffic shapping aplied to the interface.

I understand that the CEF traffic go directly to the interface's tx-ring,
and when the tx-ring is full, the packets will be queued (throught the
explicit back pressure mechanism to the L3 processor). In my scenario, I
don't understand at which level the packet drops exist.

Thanks in advance

Ariel Brunetto


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

show int pos1/0
(...)
POS1/0 is up, line protocol is up
  Hardware is Packet over Sonet
  MTU 4470 bytes, BW 155000 Kbit, DLY 100 usec,
     reliability 255/255, txload 160/255, rxload 228/255
  Encapsulation HDLC, crc 32, loopback not set
  Keepalive set (10 sec)
  Scramble enabled
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 00:13:03
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 240
                                                                      ^^^
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/184 (size/max total/threshold/drops)
     Conversations  0/175/256 (active/max active/max total)
     Reserved Conversations 2/2 (allocated/max allocated)
     Available Bandwidth 15500 kilobits/sec
  30 second input rate 108687000 bits/sec, 39212 packets/sec
  30 second output rate 97307000 bits/sec, 36663 packets/sec
     33211855 packets input, 977554890 bytes
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
              0 parity
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     28639634 packets output, 1017645702 bytes, 0 underruns
     0 output errors, 0 applique, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions


show policy interface output
(...)
    Class-map: class-default (match-any)
      42185983 packets, 14139532247 bytes
      30 second offered rate 99083000 bps, drop rate 0 bps
      Match: any
      Queueing
        Flow Based Fair Queueing
        Maximum Number of Hashed Queues 256
        (total queued/total drops/no-buffer drops) 0/240/0
                                                     ^^^

show controllers int pos 1/0
(...)
Interface POS1/0
Hardware is Packet over Sonet
 posdw_ds=0x62318ED4, base reg=0x3E000000, pc_fpga=0x3E700000,
suni_reg=0x3E600000
 no_buffers=0, no_forward=0, rx_overrun=277353563
 rx ring entries=128, tx ring entries=256
 rxring=0x7F327980, rxr shadow=0x62319460, rx_head=91, rx_tail=0
 txring=0xF327E00, txr mp shadow=0x6231968C, txr pak shadow=0x62319AB8
 tx_head=192, tx_tail=222, throttled=0 enabled=0
 tx_count=30 tx_fullring=774137144 err_int=364
             ^^^^^^^^^^^^^^^^^^^^^
 particle pool cache = 6231F9A0, cache_end = 0x5AD, PHY link up
 ip_turbo_fs = 0x6051B064


Ariel Brunetto
Systems Engineer
IP & Data Business Group
IFX NETWORKS
+54 (11) 4104 2400 Office
+54 9 (11) 5250-3832 Mobile