Catalyst 4500 Sup 7 DBL Drops

Stefan Sawluk · ‎02-25-2015

Hallo Guy´s.

I have a problem with a 4510 Switch with Sup 7 and VSS. sometimes i get from my management System a error message that i have drops. When i look at the Switch i see with a show interface the following output.

GigabitEthernet1/1/20 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet Port, address is fc5b.3981.00cb (bia fc5b.3981.00cb)
  Description: Uplink >> DEISSW28 > 0/49
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseSX
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:03, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 33588
  Queueing strategy: Class-based queueing
  Output queue: 0/40 (size/max)
  5 minute input rate 3389000 bits/sec, 396 packets/sec
  5 minute output rate 1373000 bits/sec, 375 packets/sec
     259327531 packets input, 260486639929 bytes, 0 no buffer
     Received 2197702 broadcasts (1237454 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 input packets with dribble condition detected
     687620273 packets output, 171964900087 bytes, 0 underruns
     0 output errors, 0 collisions, 6 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out

When i display the counters i see that i have DBL Drops:

Port                     InBytes       InUcastPkts      InMcastPkts       InBcastPkts
Gi1/1/20            260445332225         257093813          1237385            960186

Port                    OutBytes      OutUcastPkts     OutMcastPkts      OutBcastPkts
Gi1/1/20            171951485588         586491305         47531837          53564908

Port                   InPkts 64        OutPkts 64    InPkts 65-127    OutPkts 65-127
Gi1/1/20                  169938           2535840         73860043         571805902

Port              InPkts 128-255   OutPkts 128-255   InPkts 256-511   OutPkts 256-511
Gi1/1/20                15065293          22890554          3761375           4726098

Port             InPkts 512-1023  OutPkts 512-1023
Gi1/1/20                 2832564           3570926

Port            InPkts 1024-1518 OutPkts 1024-1518 InPkts 1519-1548 OutPkts 1519-1548
Gi1/1/20                 2133852           7956164        161468319          74102567

Port            InPkts 1549-9216 OutPkts 1549-9216
Gi1/1/20                       0                 0

Port            Tx-Bytes-Queue-1  Tx-Bytes-Queue-2 Tx-Bytes-Queue-3  Tx-Bytes-Queue-4
Gi1/1/20              3885776852          36149774        129367770         772345869

Port            Tx-Bytes-Queue-5  Tx-Bytes-Queue-6 Tx-Bytes-Queue-7  Tx-Bytes-Queue-8
Gi1/1/20               430894369          32739589        141604609      166522564649

Port            Tx-Drops-Queue-1  Tx-Drops-Queue-2 Tx-Drops-Queue-3  Tx-Drops-Queue-4
Gi1/1/20                       0                 0                1                 0

Port            Tx-Drops-Queue-5  Tx-Drops-Queue-6 Tx-Drops-Queue-7  Tx-Drops-Queue-8
Gi1/1/20                       0                 0                0                 6

Port            Dbl-Drops-Queue-1 Dbl-Drops-Queue-2 Dbl-Drops-Queue-3 Dbl-Drops-Queue-4
Gi1/1/20                        0                 0                 0                 0

Port            Dbl-Drops-Queue-5 Dbl-Drops-Queue-6 Dbl-Drops-Queue-7 Dbl-Drops-Queue-8
Gi1/1/20                        0                 0                 0             16787

Port              Rx-No-Pkt-Buff     RxPauseFrames    TxPauseFrames   PauseFramesDrop
Gi1/1/20                       0                 0                0                 0

Port            UnsupOpcodePause
Gi1/1/20                       0

Port                CrcAlign-Err  Dropped-Bad-Pkts       Collisions        Symbol-Err
Gi1/1/20                       0                 0                0                 0

Port                   Undersize          Oversize        Fragments           Jabbers
Gi1/1/20                       0                 0                0                 0

Port                  Single-Col         Multi-Col         Late-Col        Excess-Col
Gi1/1/20                       0                 0                0                 0

Port                Deferred-Col         False-Car        Carri-Sen      Sequence-Err
Gi1/1/20                       0                 0                0                 0

Port              RxIslTagFrames    TxIslTagFrames RxDot1qTagFrames  TxDot1qTagFrames
Gi1/1/20                       0                 0        257135468         683431783

On the Interface is auto qos configured.

interface GigabitEthernet1/1/20
 switchport trunk pruning vlan 2-1000
 switchport mode trunk
 auto qos trust
 service-policy input AutoQos-4.0-Input-Policy
 service-policy output AutoQos-4.0-Output-Policy

Comes this behavior from the qos? Where can i see wich traffic is assigned to queue 8?

Regards Stefan

Joseph W. Doherty · ‎02-25-2015

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Yes, DBL is a (unique to) 4500 sup QoS feature. Likely configured in your egress service-policy.

I don't recall the sup7 QoS architecture, but switches often provide fixed egress queues that you map traffic to via either CoS or ToS markings. The QoS section of the User Guide, for your IOS version, should explain.