Router interface - Total Output Drops

[zrunner626]

Can someone explain to me the reasons for the "Total Output Drops" counter incrementing when there are no other output errors?

I understand there can be drops from congestion and we are using class-based queuing. I am trying to determine if there is a problem with the ISP, because we have two sites in two cities, similar 10MB circuits (bundled T1s), using the same model router with the same QoS and sees similar traffic patterns but one has 3225716 Total output drops and the other has 977232.

Thanks

[Mark Malone · Accepted solution]

Hi

whats the drop ratio to the amount of volume thats gone through the port in total output traffic , I would work that out first to see if its an issue , there will nearly always be drops due to congestion spikes etc but if its less the 1% I wouldn't be worrying about it

burst traffic can cause drops too , floods the buffer in split second over utilising it can cause drop counter to increase , certain apps by default operate in bursty nature

can you post the show interface x/x as its is , just remove your ip if you need to

as well what platform is this different routers have different buffers etc

[zrunner626]

I noticed it previously when we had ISR2851s but in the past few weeks we swapped out both sites with ISR4331s and I was noticing the rate at theone site was growing faster again. So if I understand correctly, I divide the Total Output Drops by the Packets Output and that shows me it's less than .5% and I shouldn't worry about it...

Thanks for the help

GigabitEthernet0/2/0 is up, line protocol is up
Hardware is NIM-2GE-CU-SFP, address is 
Description: 
Internet address is x.x.x.x
MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
reliability 255/255, txload 34/255, rxload 20/255
Encapsulation ARPA, loopback not set
Keepalive not supported
Full Duplex, 10Mbps, link type is force-up, media type is RJ45
output flow-control is on, input flow-control is on
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:10, output hang never
Last clearing of "show interface" counters 3w0d
Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 3233671
Queueing strategy: Class-based queueing
Output queue: 0/40 (size/max)
5 minute input rate 813000 bits/sec, 482 packets/sec
5 minute output rate 1353000 bits/sec, 510 packets/sec
599329995 packets input, 160290504170 bytes, 0 no buffer
Received 1553 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 232696 multicast, 0 pause input
692125822 packets output, 211345146226 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

[Mark Malone]

so in the 3 weeks you cleared the counters you dropped .4 % which is not a lot for the volume of traffic gone through

Make sure your qos priority queues are not dropping traffic , if your using priority command it may cause some drops in total output as it can starve other queues and police its own queue as well so configuration can sometimes be the cause with qos , but if your voice /video queues are ok I wouldn't be worrying about it too much unless your noticing issues  in the network itself

Are you aware of all the applications running locally on your network and what way they send traffic some of them could be sending bursts adding to the problem

You should not use flow control when qos is applied it can cause issues for qos

personally I wouldn't be looking into anything less than 1% drop rate unless there is an actual issue seen but thats up to you

[goutamsingh]

You can try by changing the Negotiation as AUTO / AUTO at both end.

[alcidio.tembe1]

Dears, how are you doing? I'm good, I have this problem too...

SHOW RUN INTER GIG 0/1

interface GigabitEthernet0/1
 no ip address
 duplex auto
 speed 1000
end

SHOW INTER GIG 0/1

GigabitEthernet0/1 is up, line protocol is up
  Hardware is PQ3_TSEC, address is 58f3.9ce5.5e81 (bia 58f3.9ce5.5e81)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 6/255, rxload 2/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full Duplex, 1Gbps, media type is RJ45
  output flow-control is unsupported, input flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 1d00h
  Input queue: 0/75/17/0 (size/max/drops/flushes); Total output drops: 17501706
  Queueing strategy: Class-based queueing
  Output queue: 193/1000/19499301 (size/max total/drops)
  5 minute input rate 8952000 bits/sec, 2773 packets/sec
  5 minute output rate 23889000 bits/sec, 3413 packets/sec
     244327974 packets input, 92960216952 bytes, 0 no buffer
     Received 2535974 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 1 throttles
     6 input errors, 0 CRC, 0 frame, 6 overrun, 0 ignored
     0 watchdog, 4327 multicast, 0 pause input
     285904690 packets output, 222772863619 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     2904 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

Please help

[Adam Hinchliff]

Your input errors could indicate a cabling issue on the other end. 

[goutamsingh]

Hi ,

try changing the negotiation to Auto / Auto at both end ( ISP & Router ) , check if that makes any changes if still input drops are there then probably it's layer 1 issue.

[GerardoDuarte]

I am having the same issue and does not seem to be auto negotiation for my case. I think this is related to ISE, which I am using. Does anybody knows about this issue? I am running ISE 2.7 and will need to upgrade soon since it is EOL. But just in case if anyone has seen this interface flapping in all my switches, more than 100. The switches are 9300 :

Switch Ports Model SW Version SW Image
------ ----- ----- ---------- ----------
* 1 65 C9300-48P 17.12.03 CAT9K_IOSXE

This is the interface config:

interface GigabitEthernetx/x/x
description "Device connected"
switchport access vlan X "main vlan"
switchport mode access
switchport voice vlan 3
device-tracking attach-policy ISE-TRACKING
authentication event server dead action reinitialize vlan 2
authentication event server dead action authorize voice
authentication event server alive action reinitialize
authentication host-mode multi-auth
authentication order mab dot1x
authentication priority dot1x mab
authentication port-control auto
authentication timer reauthenticate server
authentication timer restart 65535
authentication violation restrict
mab
dot1x pae authenticator
dot1x timeout tx-period 10
spanning-tree portfast
end