output drops on cat6500 Gigabit interface

[benny]

Hi,

We saw continuous output drops on a few of our Gigabit interfaces, and can't figure out what are those output drops are and why it is happening. Anyone knows what is the reason of it and is there any way to stop the drop?

Those interfaces are all connecting to the same type of servers for the same application, so I am wondering it is the server interfaces setting, and not our switches.

Please kindly advise.

Thanks.

Ben

[vishwancc]

Hi Ben,

Could you paste the interface output.

Chao

Vishwa

[benny]

GigabitEthernet1/1 is up, line protocol is up (connected)

Hardware is C6k 1000Mb 802.3, address is 0024.4111.2329 (bia 0024.4111.2329)

Description: Server1

MTU 9014 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 55/255, rxload 57/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

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

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

Clock mode is auto

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

Last input never, output 00:00:44, output hang never

Last clearing of "show interface" counters 00:30:47

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 5768

Queueing strategy: fifo

Output queue: 0/40 (size/max)

1 minute input rate 225412000 bits/sec, 19598 packets/sec

1 minute output rate 216025000 bits/sec, 3552 packets/sec

36362554 packets input, 52446340542 bytes, 0 no buffer

Received 29 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

6347453 packets output, 49296069677 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

[iyde]

So you are saying that you have the same type of servers sitting off from those ports? How are those servers reporting the statistics from their NIC? Do you see any errors there?

Output drops, in my understanding, happens when you try to send more data out an interface than can be received by the equipment at the other end.

I see that you have a 1 minute output rate of appx. 216 Mbps. Could it be that your servers simply are not able to handle that amount of data? Remember that even though the NIC is running at 1 Gbps you cannot be sure that the internal bus, memory etc. can handle that load.

HTH

[benny]

Thanks for the reply.

I will have to check with the server admin for the server NIC statistics. But in your opinion, it is not that the switch output queue is too small, and the output traffic is too much, that the switch is dropping packets in the output queue becuase of the queue size is set too small?

Thanks!

Ben