Cisco 6509 total output drop

[stanleylin1986]

Hi All
近期觀察到Cisco 6509 上的interface有Total output drop出現，對接的設備是在其他樓層的cisco switch 3524,不曉得該如何處理
相關interface log請參閱以下

6509-OA#sh run int gi 7/46
interface GigabitEthernet7/46
description
switchport
switchport mode trunk
no ip address
end

6509-OA#sh int gi 7/46
GigabitEthernet7/46 is up, line protocol is up (connected)
Hardware is C6k 1000Mb 802.3, address is 0011.9298.d3a1 (bia 0011.9298.d3a1)
Description: A-HQ14F-A020620-OP
MTU 1500 bytes, BW 100000 Kbit, DLY 10 usec,
reliability 255/255, txload 64/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/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 00:00:33, output 00:00:02, output hang never
Last clearing of "show interface" counters 5w4d
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 236672777
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 68000 bits/sec, 34 packets/sec
5 minute output rate 25429000 bits/sec, 5312 packets/sec
173333928 packets input, 58845989538 bytes, 0 no buffer
Received 55386189 broadcasts (49023862 multicasts)
0 runts, 0 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
5921612450 packets output, 3730501839036 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

6509-OA#sh queueing int gi 7/46
Interface GigabitEthernet7/46 queueing strategy: Weighted Round-Robin

QoS is disabled globally
Port is untrusted
Extend trust state: not trusted [COS = 0]
Default COS is 0
Queueing Mode In Tx direction: mode-cos
Transmit queues [type = 1p2q2t]:
Queue Id Scheduling Num of thresholds
-----------------------------------------
1 WRR low 2
2 WRR high 2
3 Priority 1

WRR bandwidth ratios: 255[queue 1] 1[queue 2]
queue-limit ratios: 100[queue 1] 0[queue 2] 0[Pri Queue]*same as Q2

queue random-detect-min-thresholds
----------------------------------
1 100[1] 100[2]
2 100[1] 100[2]

queue random-detect-max-thresholds
----------------------------------
1 100[1] 100[2]
2 100[1] 100[2]

queue thresh cos-map
---------------------------------------
1 1 0 1 2 3 4 5 6 7
1 2
2 1
2 2
3 1

Queueing Mode In Rx direction: mode-cos
Receive queues [type = 1q2t]:
Queue Id Scheduling Num of thresholds
-----------------------------------------
1 Standard 2

queue tail-drop-thresholds
--------------------------
1 100[1] 100[2]

queue thresh cos-map
---------------------------------------
1 1 0 1 2 3 4 5 6 7
1 2

Packets dropped on Transmit:
BPDU packets: 0

queue thresh dropped [cos-map]
---------------------------------------------------
1 1 33844276 [0 1 2 3 4 5 6 7 ]
* - shared transmit counter

Packets dropped on Receive:
BPDU packets: 0

queue thresh dropped [cos-map]
---------------------------------------------------
1 1 0 [0 1 2 3 4 5 6 7 ]

[Lei Zhang · Accepted solution]

您好！
Total output drops，简单来说，是由于该接口出方向buffer不够，导致的丢包现象。
通常引起该问题的几个原因：
1、不恰当的QoS配置。
2、入接口与出接口速率不匹配。即一个流量从本6509的Ten 1/1进来（实际流量8G），出接口G 2/1(只能发出1G)。
3、多个入接口流量从一个出接口发出。即G1/1（实际1G流量）、G1/2（实际1G流量）、G1/3（实际1G流量）进来，恰好都需要从G2/1（1G）接口发出。
4、突发流量产生。即入接口G1/1，出接口G2/1，通过show interface或者网管设备查看到平均流量不是很高。但并不能证明没有突发流量产生。突发流量定义：Burst is defined as the amount of traffic (generally measured in bytes) transmitted per millisecond which exceeds the per-second average.
所以，需要在出接口（即产生output drop的接口）发生问题时抓包（不用抓太久），用wireshark、sniffer的流量绘图功能，将时间轴调整至毫秒级，看流量图是否有明显的波峰或波谷。如有，则突发流量真实存在。
希望可以帮到你！
谢谢！

[Luke Huang]

Total output drops: 236672777，是历史累积值，还是随着时间有增长？

[chandler]

Total output drops：是对接口的buffer处理output方向的数据不及时或因为有突发流量超过接口每毫秒的处理能力就丢掉的数据包统计。
这个你要看看丢包频率怎么样，如果频率不是太大可以忽略。
如果频率较高可使用QOS控制流量减轻buffer的处理压力，降低output丢包，或查找异常数据源设备处理突发流量的原因导致的output丢包