Interface output drops

[Azeem Dawood]

Dear All,

I don't know how to resolve a problem like output drops on an interface (cisco 6500). On my 6500 switchport a server is connected directly but usually only on that interface i can see a large amount of drops from output queue.

If anyone knows how to resolve this problem pls help me.

Pls see the below output from the affected interface...

GigabitEthernet2/20 is up, line protocol is up (connected)

  Hardware is C6k 1000Mb 802.3, address is xxxxxxxxx

  Description: xxxxxxx

  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

     reliability 255/255, txload 2/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex, 1000Mb/s

  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 00:00:11, output hang never

  Last clearing of "show interface" counters 01:20:04

  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 26652872

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 786000 bits/sec, 610 packets/sec

  5 minute output rate 10517000 bits/sec, 1877 packets/sec

     2962329 packets input, 481699583 bytes, 0 no buffer

     Received 1683 broadcasts (111 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

     10821851 packets output, 6542469256 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,

Azeem

[mahmoodmkl]

Hi,

Can you confrrim whether the line card is fully utilized.

Thanks

[Azeem Dawood]

Dear Mahmood,

Thanks for the reply. Yes the line card id fully utilized but ouput drops comes for this interface only.

Thanks

[mahmoodmkl]

Hi,

I think it is due to over subscription issue with the line card or with the cabling.

Kindly invetigate the subscription ratio and cabling.

Thanks

[Azeem Dawood]

OK. Many thanks. But will be happy to know what had caused this thing. Only physical layer problem can initiate this issue output drops.

any other technique to figure out physical layer problem.

[Leo Laohoo]

Good point.

Exactly WHAT model is the line card?  If it's NOT a 67XX line card then you have a problem.  This is because the 67XX line card is designed for high-speed servers.  61XX, 63XX and 65XX are NOT designed to be connected to servers.

[Azeem Dawood]

Thanks for your reply,

My line card model is 6500, but as you said this line card is not meant for the high speed servers, would like to tell you that only few servers are facing this problem and those servers are not even that critical. Moreover one of the server is simply a workstation on which a server image is installed. So what do you think now? ok i will check by connecting a new network cable n hope that issue will get resolve but not sure.

Many thanks again.

[Joseph W. Doherty]

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Posting

Many of the Catalyst line cards share hardware resources across multiple ports, even 67xx line cards.  Exceeding the hardware resources will often lead to drops.  So, you can try to not exceed shared resources by how you share/utilize them.

For instance, your cards might share output buffers across groups of 8 ports.  Such a line card might only support true wire rate using just 1 of its 8 ports (in same group).  If you have such a busy port, you might find you have to not use the other 7 ports within the same group.  Similar consideration for other combinations.  For a group of 8, two ports at 25% and one port at 50% utilization averages might be fine.

You might find just redistributing ports by usage, across the port groups, will benefit overall performance.  For example, you might place the busiest and least busy port in the 1st group, 2nd busiest and 2nd least busiest in 2nd group, etc.

[Azeem Dawood]

Thanks,

I will do that..