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Community Member

Output drops

Hi all,

I am having lot of output packet drops. I just want to know what kind of traffic it is dropping and what is causing it. For your information the interface f1/30 is connected to a 3rd party QOS box. I have tried all the troubleshooting steps, changing cables, checking mls stats. If you need more information I can provide it to u.

Statistics for Earl in Module 5

L2 Forwarding Engine

Total packets Switched : 6265369

L3 Forwarding Engine

Total packets L3 Switched : 6245992 @ 6666 pps

Total Packets Bridged : 3846350

Total Packets FIB Switched : 152

Total Packets ACL Routed : 0

Total Packets Netflow Switched : 0

Total Mcast Packets Switched/Routed : 16665

Total ip packets with TOS changed : 26816

Total ip packets with COS changed : 612329

Total non ip packets COS changed : 0

Total packets dropped by ACL : 8037

Total packets dropped by Policing : 0

Total packets exceeding CIR : 0

Total packets exceeding PIR : 0


MAC/IP length inconsistencies : 0

Short IP packets received : 0

IP header checksum errors : 0

TTL failures : 0

MTU failures : 0

Total packets L3 Switched by all Modules: 6245992 @ 6666 pps

sh int f1/30

FastEthernet1/30 is up, line protocol is up (connected)

Hardware is C6k 100Mb 802.3, address is 0019.e8d7.9ed5 (bia 0019.e8d7.9ed5)


MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

reliability 255/255, txload 12/255, rxload 25/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input never, output 00:00:20, output hang never

Last clearing of "show interface" counters 00:15:19

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1307

Queueing strategy: fifo

Output queue: 0/40 (size/max)

30 second input rate 9905000 bits/sec, 1841 packets/sec

30 second output rate 5022000 bits/sec, 1806 packets/sec

1572849 packets input, 892467909 bytes, 0 no buffer

Received 277 broadcasts (201 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

1546539 packets output, 492746040 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


Switching path Pkts In Chars In Pkts Out Chars Out

Processor 0 0 15 7155

Route cache 0 0 0 0

Distributed cache 0 0 0 0

Total 0 0 15 7155


Super Bronze

Re: Output drops

Total output drops: 1307

1546539 packets output

= 0.084%

Normally, such a drop percentage shouldn't be an issue. Some drops are normal due to TCP flows attempting to utilize full bandwidth.

Community Member

Re: Output drops

Hi there,

Tks for the information. I know this time the packet drop is very less but some times it is between 3-5% ( in less than 5 minutes) not sure why.

Super Bronze

Re: Output drops

Well, that could still be TCP flow(s) trying to use all the bandwidth. It could also be a heavy, relative to bandwidth, non-TCP flow(s), or a combination of both. If traffic offers more than link capacity, interfaces, at first, often queues bursts. If traffic continues to offer more than link capacity, queue overflows and packets are discarded and recorded as drops.

If you really want to see what's going on, you could tap into NetFlow stats (if available on your platform) or span the the port (if available on the platform) and capture traffic for examination.

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