Interface Outdiscard in CISCO 2960

[Arijit007]

We are getting high amount of outdiscard in one of our CISCO 2960 interface. When run sh int command we found below output. 

reliability 255/255, txload 17/255, rxload 25/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:00, output hang never
Last clearing of "show interface" counters 46w3d
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 12536042
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 9908000 bits/sec, 2285 packets/sec
5 minute output rate 6842000 bits/sec, 2280 packets/sec
71823866956 packets input, 47100116953127 bytes, 0 no buffer
Received 216742381 broadcasts (215750842 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 215750842 multicast, 0 pause input
0 input packets with dribble condition detected
63940048141 packets output, 24372644910578 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
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

now wanted to know below details-

1> How to know the overall drops in percentage? (How to calculate)

2> What is the CISCO recommended threshold? 

3> What we can do reduce this high value of discards? 

[Mohsin Alam]

Can you clear the counters , it was last cleared 46 days ago.

If it's incrementing even after that you will need to take span and check for microburst traffic.

https://www.cisco.com/c/en/us/support/docs/lan-switching/switched-port-analyzer-span/116260-technote-wireshark-00.html

Do you have any QOS?

Try getting multiple output of show int <> hu 

and see how drops are incrementing or they are historical.

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[Arijit007]

Previously we cleared the counters but issue still persists. it is very often we get the discards alert for this switch. 

QOS is not enabled for this interface. 

show int <> hu --> tried to run this command gave error. 

[Mohsin Alam]

alrighty, yup your IOS is old hence you cannot run that command. 
Did you check out the link i shared?
Also consider upgrading your IOS to latest stable.

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[Arijit007]

I have checked the link. Now to do that i need to check within team.

Apart from this what else i can check or do to solve this?

Also could you please let me know what could cause 'Input Discards' error? 

[Georg Pauwen]

Hello,

check if your IOS supports the command:

qos queue-softmax-multiplier 1200

If that command is not available, and if you have 'mls qos' enabled, try and disable it altogether (no mls qos), that sometimes helps to eliminate the drops.

You could also try some generic queue tuning:

mls qos

!

mls qos queue-set output 1 threshold 1 3200 3200 25 3200
mls qos queue-set output 1 threshold 2 3200 3200 25 3200
mls qos queue-set output 1 threshold 3 3200 3200 25 3200
mls qos queue-set output 1 threshold 4 3200 3200 25 3200

[Arijit007]

QOS is not enabled for that interface. 

[balaji.bandi]

First i see it 100MB

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

Many Drops :

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 12536042

sh int gx/x counter error

show platform qos queue config gigabitEthernet x/x

show version

[Arijit007]

1> sh int gi1/0/10 counters errors

Port                  Align-Err FCS-Err Xmit-Err Rcv-Err UnderSize   OutDiscards
Gi1/0/10                     0           0            0          0               0      12574759

Port                  Single-Col Multi-Col Late-Col Excess-Col Carri-Sen Runts Giants
Gi1/0/10                   0                 0           0                 0                0       0          0

2> Sh version

Ports         Model                           SW Version
-----       -----                              ----------
28       WS-C2960X-24TS-L          15.0(2a)EX5

QOS is not configured for that interface.

show platform qos queue config gigabitEthernet x/x is not available in switch. 

[Joseph W. Doherty]

On a 2960, often microbursts will overrun buffer resources, resulting in drops.  "Default" QoS settings, with QoS active, will often increase microburst drop rate due to QoS "reserving" buffer resources for each, of four, egress queues.

If drops are due to microbursts, and/or transient congestion, sometimes drop rate can be reduced (sometime also by a lot) by changing QoS settings (the second set of QoS settings provided by Georg, if QoS needed to be used, are a good start).

If drops are due to sustained congestion, either you need to provide additional bandwidth (as hinted by Balaji noted 100 Mbps being used) and/or better manage/control drops (difficult on a 2960).

Lastly, you didn't mention which model 2960, but I believe (?) the 48 port models divide hardware resources between banks of 24 copper ports and possibly uplink ports.  If correct, having distribution of which bank your congested ports are using, might impact drop rates too.