output drops in cisco switch 2960

[singhaam007]

                   Hi there,

We are getting some packet drops on our some 2960 switchs.

sh int f0/27 | inc drops|bits

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 10297

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

5 minute output rate 6000 bits/sec, 3 packets/sec

And users are complaining about slow network and taking long to open any network drives.

It’s a (C2960-HBOOT-M) Version 12.2(46r)SE2 lanbasek9-mz.122-55.SE3.bin

But there is not much traffic going trough and we still getting drops

FastEthernet0/27 is up, line protocol is up (connected)

Hardware is Fast Ethernet, address is

Description: Level 11 VoIP and Data Connection

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

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

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

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

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

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

Last input 2w0d, output 00:00:00, output hang never

Last clearing of "show interface" counters 1w3d

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 10297

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 3000 bits/sec, 3 packets/sec

5 minute output rate 30000 bits/sec, 7 packets/sec

     408520 packets input, 102710312 bytes, 0 no buffer

     Received 220 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

     1695780 packets output, 686477375 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

sh int f0/27 counters errors

Port       Align-Err     FCS-Err   Xmit-Err     Rcv-Err UnderSize OutDiscards

Fa0/27             0           0                  0               0         0                    10297

Please help.

thanks

[Arumugam Muthaiah]

Hi Amrinder,

These outdiscards counters indicate that the switch could not buffer all the packets that came in on that port a that moment of time, which happens when the traffic is bursty in nature

• Basically Output drops represent egress traffic dropped due to momentarily exceeded wire capacity.
  
• Many ingress links sending bursty traffic to one egress link
  
• Traffic burst and sustained traffic rate combination may cause output drops
  

Please change the load interval from 5 mins to 30 secs and it does not cause anything to work differently. By setting the load-interval to a shorter value you may see more easily the impact of bursty traffic which is one of the cause for output drops

Ex:
Switch(Config)#int fa0/27
Switch(Config-if)#load-interval 30
Switch(Config-if)#exit

What type of interface fa0/27 it is?

do you see this output drops continuously or intermittent?

is the mls qoq enabled?

Clear the counter and verify the below commands, and check does the output drops incrementing continuously

#show int f0/27 | inc drops|bits

#show int f0/27 counters errors

#show mls qos int <interfa-id> statistics
#show platform port-asic stats drop fa0/7
#sh controllers ethernet-controller fa0/7

Regards,

Aru

[singhaam007]

Hi Arumugam ,

thanks for helping me out here.

we changed the interval to 30 seconds.

Actually, this is a voice and data port. Therefore, we remove the voice vlan to see if it stop packet drop. However, the thing is user complaining slow network as well. I am monitoring the port in cacti and drops are around 6 am in the morning and no one was in office.

So at end we remove the qos config from this port to see if we still getting drops.

Drops are not continuously they just intermittent.

There was no traffic going through and in the morning and we still getting drops.

any idea??

thanks for your help.

[Leo Laohoo]

Duplicate post #2.