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Huge amount of Total output drops

I am seeing the "Total output drops" and "txload" go up. What should I look at for this. I do not see any other errors?

GigabitEthernet1/2/42 is up, line protocol is up (connected)

Hardware is C6k 1000Mb 802.3, address is 0011.9299.bb49 (bia 0011.9299.bb49)

Description: ROC80 (62)

MTU 9216 bytes, BW 100000 Kbit, DLY 10 usec,

reliability 255/255, txload 17/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, media type is 10/100/1000BaseT

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

Clock mode is auto

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

Last input never, output 00:00:02, output hang never

Last clearing of "show interface" counters 01:43:13

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1306379

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 6721000 bits/sec, 878 packets/sec

0 packets input, 0 bytes, 0 no buffer

Received 0 broadcasts (0 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

5117480 packets output, 4758857198 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

Thanks,

Mike

10 REPLIES
Purple

Re: Huge amount of Total output drops

Make sure the speed and duplex are set exactly the same on both ends of that link , if one end is hardcoded and the other is auto that can cause problems . Check to make sure both ends are set up for giant packets also as I see the mtu size is 9216 .

Re: Huge amount of Total output drops

I will check that but wouldn't I see other errors if the speed and duplex were different? I will also check the giant packets on both sides.

Thanks,

Mike

Re: Huge amount of Total output drops

I think I may have found the problem. Correct me if I am wrong...

If I Team two NIC's in a server I have to setup the switchports in an ether-channel....correct?

Mike

Super Bronze

Re: Huge amount of Total output drops

What you might "look at" is what type of traffic is passing across this interface. Assuming your counters are correct, a 25% drop percentage may indicate insufficient bandwidth for non-TCP traffic or such traffic is very bursty. If the latter, increasing the output queue size might help (or use WRED, not for early drop, but for its average queue size feature).

Re: Huge amount of Total output drops

I will check all that. What is WRED? Also it might be bursty as I keep checking it and it stays the same for about 30 seconds and then it increments up and stays again....

ROC-6509-VSS#show int gi1/2/42 | inc txload|Total output drops

reliability 255/255, txload 14/255, rxload 1/255

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1852644

ROC-6509-VSS#show int gi1/2/42 | inc txload|Total output drops

reliability 255/255, txload 14/255, rxload 1/255

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1852644

ROC-6509-VSS#show int gi1/2/42 | inc txload|Total output drops

reliability 255/255, txload 15/255, rxload 1/255

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1852716

ROC-6509-VSS#show int gi1/2/42 | inc txload|Total output drops

reliability 255/255, txload 15/255, rxload 1/255

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1852716

ROC-6509-VSS#show int gi1/2/42 | inc txload|Total output drops

reliability 255/255, txload 15/255, rxload 1/255

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1852716

ROC-6509-VSS#show int gi1/2/42 | inc txload|Total output drops

reliability 255/255, txload 15/255, rxload 1/255

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1852716

See how it went up.

Mike

Super Bronze

Re: Huge amount of Total output drops

Re: Huge amount of Total output drops

Thanks. I will check that out.

Mike

Community Member

Re: Huge amount of Total output drops

Output drops are caused because the hardware queue can't send the packet. Meaning you might have a performance issue or a buffer issue somewhere.

Most of the time these errors occur on interfaces connected to routers because the output speed is usually much slower than the input speed, for example 100Mb Ethernet LAN and only a 2Mb WAN link.

Purple

Re: Huge amount of Total output drops

If this is a server is the server nic setup to handle giant packets ?

Re: Huge amount of Total output drops

Yes it had that setup. I did find an issue with the NIC and how teaming and etherchanneling was setup. I am going to update the NIC driver and make some needed configuration changes after the 1st of the year. Right now I disabled the NIC and the output errors went away.

Mike

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