finding error rate on interface - output drops are in packets or bytes?

[geo555]

Hi everyone,

I want to calculate the percentage of errors on an interface and I have searched a lot of posts and some people divide output drops by output packets, and some by output bytes. And some also add the OD on the denominator. What is correct?

if

OD = output drops

OP = output packets

OB = output bytes

is error rate OD/OP x 100 or OD/OB x 100 or OD/(OD+OP) or OD/(OD+OB) ?

Here is my interface stats

Last clearing of "show interface" counters 01:23:29

 Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 102807820

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 17511000 bits/sec, 9009 packets/sec

  5 minute output rate 38952000 bits/sec, 9419 packets/sec

     37716038 packets input, 9939151626 bytes, 0 no buffer

     Received 38514 broadcasts (166 multicasts)

     0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 166 multicast, 0 pause input

     0 input packets with dribble condition detected

     42410649 packets output, 25099609208 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

Many thanks,

george

[geo555]

now that I see my own numbers, it has to be bytes!

[Georg Pauwen]

Hello,

the numbers are all in bytes as far as I recall.

[Georg Pauwen]

Hello,

what switch model is this on ? Post the output of:

sh interfaces x

where 'x' is the interface having the output errors.

[geo555]

the device is nexus 9300

GigabitEthernet1/0/x is up, line protocol is up (connected) 
  Hardware is Gigabit Ethernet, address is 70d3.7985.a68c (bia 70d3.7985.a68c)
  Description: xxxxx
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec, 
     reliability 255/255, txload 9/255, rxload 4/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/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 00:00:05, output hang never
  Last clearing of "show interface" counters 01:23:29
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 102807820
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 17511000 bits/sec, 9009 packets/sec
  5 minute output rate 38952000 bits/sec, 9419 packets/sec
     37716038 packets input, 9939151626 bytes, 0 no buffer
     Received 38514 broadcasts (166 multicasts)
     0 runts, 0 giants, 0 throttles 
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 166 multicast, 0 pause input
     0 input packets with dribble condition detected
     42410649 packets output, 25099609208 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

[Georg Pauwen · Accepted solution]

Hello,

try and configure:

qos queue-softmax-multiplier 1200

on your 9300 switch and check if the drops decrease...

[geo555]

Hi thanks,

I applied this command and my drops are zero.

From my understanding the drops were due to microbursts and the low buffer size of 9300 egress queue which is shared by many ports.

[Giuseppe Larosa]

Hello @geo555 ,

my understanding is that output drops is the number of packets dropped on the interface at least on routers.

The formula I use for error ratio is =   OD / (OD+OP) *100

I agree you have a very high number of output drops.

Edit:

For Nexus 3000 I have found the following

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus3000/sw/command/reference/931m3k/show/b_N3K_Show_Commands_93x_n3k/b_N3K_Show_Commands_93x_n3k_chapter_01011.html#wp3576411209

it does not tell if it is in packets or bytes I remember on routers from QoS tests testing CBWFQ with traffic generator it was a packet counter and then with show policy-map int we could see also the byte counters.

Hope to help

Giuseppe

[geo555]

Hi Giuseppe, this is a switch. If you look at the number it cannot be packets, because then the number of packet drops would be larger than the output packets, which means my packet loss would be > 100%