[c-nsp] Need help w/ output drops on 7613 WS-X6748-GE-TX

[Hank Nussbacher]

We have a 7613 w/ WS-SUP720-3BXL running 12.2(18)SXF11.
We have a 48 port WS-X6748-GE-TX.  On one interface we
continue to see output drops when traffic goes above 200Mb/sec.

The interface is defined as follows (very straightforward):
interface GigabitEthernet9/29
  mtu 9000
  bandwidth 1000000
  no ip redirects
  no ip unreachables
  ip route-cache flow
  ip ospf message-digest-key 1 md5 7 xxxxxx
  ip ospf network point-to-point
  load-interval 30
  hold-queue 4096 out

GigabitEthernet9/29 is up, line protocol is up (connected)
   Hardware is C6k 1000Mb 802.3, address is 0015.2c87.b240 (bia 0015.2c87.b240)
   MTU 9000 bytes, BW 1000000 Kbit, DLY 10 usec,
      reliability 255/255, txload 70/255, rxload 9/255
   Encapsulation ARPA, loopback not set
   Keepalive set (10 sec)
   Full-duplex, 1000Mb/s
   input flow-control is off, output flow-control is off
   Clock mode is auto
   ARP type: ARPA, ARP Timeout 04:00:00
   Last input 00:00:07, output 00:00:03, output hang never
   Last clearing of "show interface" counters 15:19:33
   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1385749
   Queueing strategy: fifo
   Output queue: 0/4096 (size/max)
   30 second input rate 39197000 bits/sec, 15438 packets/sec
   30 second output rate 276768000 bits/sec, 27265 packets/sec
   L2 Switched: ucast: 15526 pkt, 90533934 bytes - mcast: 6338 pkt, 944440 
bytes
   L3 in Switched: ucast: 673843076 pkt, 151541187645 bytes - mcast: 0 pkt, 
0 bytes mcast
   L3 out Switched: ucast: 1227451580 pkt, 1367583751541 bytes mcast: 0 
pkt, 0 bytes
      673834038 packets input, 151610506124 bytes, 0 no buffer
      Received 54234 broadcasts (0 IP multicasts)
      0 runts, 10000 giants, 0 throttles
      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
      0 watchdog, 0 multicast, 0 pause input
      0 input packets with dribble condition detected
      1225945267 packets output, 1365797313199 bytes, 0 underruns
      0 output errors, 0 collisions, 0 interface resets
      0 babbles, 0 late collision, 0 deferred
      0 lost carrier, 0 no carrier, 0 PAUSE output
      0 output buffer failures, 0 output buffers swapped out
---------------------------------------------------------------------------------
Editted "sho platform hardwa capa":

Forwarding engine load:
                      Module       pps   peak-pps                     peak-time
                      7         186009    1442340  12:41:38 IDT Tue Sep 22 2009
                      9         232549     450263  22:10:57 IST Wed Nov 24 2010

Switch Fabric Resources
   Bus utilization: current: 0%, peak was 6% at 01:04:03 IST Sat May 29 2010
   Fabric utilization:     Ingress                    Egress
     Module  Chanl  Speed  rate  peak                 rate  peak
     9       0        20G    2%    9% @18:39 15Dec10    7%   16% @15:14 23Nov10
     9       1        20G    0%    6% @08:20 25Aug10    1%    8% @20:51 25Jan10

Interface Resources
   Interface drops:
     Module    Total drops:    Tx            Rx      Highest drop port:  Tx  Rx
     9                   18521265       1032837                          14  12
----------------------------------------------------------------------------------
Results for "sho mls stat module 9"

Statistics for Earl in Module 9

L2 Forwarding Engine
   Total packets Switched                : 13534106672944

L3 Forwarding Engine
   Total packets L3 Switched             : 7264929316950 @ 228064 pps

   Total Packets Bridged                 : 3492211276
   Total Packets FIB Switched            : 7210651379282
   Total Packets ACL Routed              : 0
   Total Packets Netflow Switched        : 1
   Total Mcast Packets Switched/Routed   : 68097738
   Total ip packets with TOS changed     : 38527077597
   Total ip packets with COS changed     : 5186771
   Total non ip packets COS changed      : 0
   Total packets dropped by ACL          : 2480178486
   Total packets dropped by Policing     : 5999570
   Total packets exceeding CIR           : 7349955
   Total packets exceeding PIR           : 7349955

Errors
   MAC/IP length inconsistencies         : 303
   Short IP packets received             : 0
   IP header checksum errors             : 140
   TTL failures                          : 933512031
   MTU failures                          : 186689

----------------------------------------------------------------------------------
gp#sho int gi9/29 flow
Port    Send FlowControl  Receive FlowControl  RxPause TxPause
         admin    oper     admin    oper
-----   -------- -------- -------- --------    ------- -------
Gi9/29  desired  off      off      off         0       0
gp#sho int gi9/29 stats
GigabitEthernet9/29
           Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                Processor      17357   91475075      17485   91588871
              Route cache          0          0          1         40
        Distributed cache  683233031 154080580279 1244084298 1388566226885
                    Total  683250388 154172055354 1244101784 1388657815796
gp#sho int gi9/29 capa
GigabitEthernet9/29
   Dot1x:                 yes
   Model:                 WS-X6748-GE-TX
   Type:                  10/100/1000BaseT
   Speed:                 10,100,1000,auto
   Duplex:                half,full
   Trunk encap. type:     802.1Q,ISL
   Trunk mode:            on,off,desirable,nonegotiate
   Channel:               yes
   Broadcast suppression: percentage(0-100)
   Flowcontrol:           rx-(off,on,desired),tx-(off,on,desired)
   Membership:            static
   Fast Start:            yes
   QOS scheduling:        rx-(2q8t), tx-(1p3q8t)
   CoS rewrite:           yes
   ToS rewrite:           yes
   Inline power:          no
   SPAN:                  source/destination
   UDLD                   yes
   Link Debounce:         yes
   Link Debounce Time:    no
   Ports on ASIC:         25-36
   Port-Security:         yes


How can we determine what is causing these output drops?  What are we missing?

Thanks,
Hank