2960 Output Drops

[ALIAOF_]

I have a Cisco 2960 switch connected to a 4948E via port channel and I'm seeing output drops on the 2960 on the port channel.  On the 4948 where it is connected I don't see any input or output errors.  Could it be just because of the smaller buffer size on that switch.  I cleared the interface yesterday and today number is up to 79880?

Now 2960 does not have speed and duplex hard coded I don't even get those command options on that switch for the two interfaces.  But I have them hard coded on the 4948E. 

IOS

2960 Port Config: 12.2(44)SE6, RELEASE SOFTWARE (fc1)

interface GigabitEthernet0/45

description Trunk ports to 4948

switchport mode trunk

channel-group 1 mode on

!

interface GigabitEthernet0/46

description Trunk ports to 4948

switchport mode trunk

channel-group 1 mode on

!

4948 Port Config: 5.1(1)SG1, RELEASE SOFTWARE (fc2)

interface Port-channel11

description Port Channel for 2960

switchport

switchport mode trunk

!

interface GigabitEthernet1/35

description Trunk Ports to 2960

switchport mode trunk

speed 1000

duplex full

channel-group 11 mode on

spanning-tree guard root

!

interface GigabitEthernet1/36

description Trunk Ports to 2960

switchport mode trunk

speed 1000

duplex full

channel-group 11 mode on

spanning-tree guard root

Port-channel1 is up, line protocol is up (connected)

  Hardware is EtherChannel, address is 0026.0a73.1eae (bia 0026.0a73.1eae)

  Description: Port Channel to xxxxxxxxxxxxxxxxxxxxxxxxxx

  MTU 1500 bytes, BW 2000000 Kbit, DLY 10 usec,

     reliability 255/255, txload 7/255, rxload 10/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex, 1000Mb/s, link type is auto, media type is unknown

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

  Members in this channel: Gi0/45 Gi0/46

  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 21:11:45

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 79880

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 79808000 bits/sec, 11659 packets/sec

  5 minute output rate 60703000 bits/sec, 11033 packets/sec

     578360696 packets input, 346231331921 bytes, 0 no buffer

     Received 1425403 broadcasts (1098226 multicasts)

     0 runts, 0 giants, 0 throttles

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

     0 watchdog, 1098226 multicast, 0 pause input

     0 input packets with dribble condition detected

     955600443 packets output, 1113883265239 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

[Gregory Snipes]

Could you post up the "show interface" for all of the physical ports? It could be a problem with one of the underlying links.

[ALIAOF_]

Here you go, I didn't post 4948E interfaces because there are no errors on them

2960 Interfaces:

GigabitEthernet0/45 is up, line protocol is up (connected)

  Hardware is Gigabit Ethernet, address is 0026.0a73.1ead (bia 0026.0a73.1ead)

  Description: Trunk ports to xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

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

     reliability 255/255, txload 2/255, rxload 5/255

  Encapsulation ARPA, loopback not set

  Keepalive not set

  Full-duplex, 1000Mb/s, link type is auto, 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 00:00:22, output 00:00:01, output hang never

  Last clearing of "show interface" counters 21:53:54

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 31236

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 21380000 bits/sec, 3908 packets/sec

  5 minute output rate 8455000 bits/sec, 3794 packets/sec

     348381456 packets input, 203766234913 bytes, 0 no buffer

     Received 1102063 broadcasts (968765 multicasts)

     0 runts, 0 giants, 0 throttles

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

     0 watchdog, 968765 multicast, 0 pause input

     0 input packets with dribble condition detected

     497218593 packets output, 557907548052 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

----------------------------------------------------------------------------------------------------------------------------

GigabitEthernet0/46 is up, line protocol is up (connected)

  Hardware is Gigabit Ethernet, address is 0026.0a73.1eae (bia 0026.0a73.1eae)

  Description: Trunk ports to xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

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

     reliability 255/255, txload 6/255, rxload 5/255

  Encapsulation ARPA, loopback not set

  Keepalive not set

  Full-duplex, 1000Mb/s, link type is auto, 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 00:00:29, output 00:00:09, output hang never

  Last clearing of "show interface" counters 21:54:34

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 48747

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 20308000 bits/sec, 3712 packets/sec

  5 minute output rate 26354000 bits/sec, 3777 packets/sec

     251517274 packets input, 157512429843 bytes, 0 no buffer

     Received 372523 broadcasts (165975 multicasts)

     0 runts, 0 giants, 0 throttles

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

     0 watchdog, 165975 multicast, 0 pause input

     0 input packets with dribble condition detected

     479015579 packets output, 567863354471 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

[Gregory Snipes]

Could you post up the configs for the 2960 as well? I am interested in comparing the two.

[ALIAOF_]

Here it is.

[Gregory Snipes]

I apologize for my mistyping. I really wanted the show interface from the 2960.

[ALIAOF_]

No problem I posted it above unless you are asking for show interfaces for all the interfaces?

[Gregory Snipes]

Yes, all the interfaces would be beneficial.

[paolo bevilacqua]

Do you have any QoS configured on the 2960 ?

[ALIAOF_]

No here is a "show mls qos"

QoS is disabled

QoS ip packet dscp rewrite is enabled

[InayathUlla Sharieff · Accepted solution]

HI Ali,

The counter "Total output drops:" is incremented each time the output queue

was overloaded, and therefore some packets had to be dropped due to a lack

of

output buffers. If this counter for output drops was incrementing while you

are on the

router, and you did a "show interface", the output queue would most

definitely have been 40/40,

which means it was full. If the output queue is 0/40 like in the capture you

provided, the

output drops should not be incrementing at that particular time.

The output queue can become full during periods where the interface is

sending close to full capacity of traffic, or if there are short bursts of

high traffic rates that needs to go out on that interface.

1) If you clear the counters, how is the rate of the output drop

accumulation?

2) Verify that the cable is good by using a cable tester or replace it with

a known good cable.

3) Verify that the Network Interface Card (NIC) is compatible and working

properly. Refer to

< http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tec

h_note09186a00800a7af0.shtml>

http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tech

_note09186a00800a7af0.shtml

4) Verify that the flow control settings are the same on both sides of a

Ethernet link.

Action plan:

kindly apply the following:

- Change the load interval from 5 minute to 30 seconds >> load-interval 30

"under the interface mode "

- Clear the counters.

- After that if you would still see the discards increasing , please capture

the following commands 2-3 times (1 minute interval between each output)

#sh controllers

#sh interfaces

#show interface counter error

#show platform port-asic stats drop

#sh interface interface-ID | i output drop

#show mls qos int stat   ////////this for the interfaces seeing the

output drops

Regards

Inayath

[ALIAOF_]

Thanks so much for an excellent reply makes a whole lot sense and I understand.  Yes the output queue indeed is always 0/40 and while I'm logged in there I don't see the increments.  I think there might be short bursts of traffic that might be causing this.  Here are the answers to your first part questions:

1) If you clear the counters, how is the rate of the output drop

accumulation?

**** No after changing the load interval and clearing the counters while I'm logged in I saw 15 drops after like 30 min (on gi0/46)****

2) Verify that the cable is good by using a cable tester or replace it with

a known good cable.

**** Tested the two cables before I kind of do whenever I plug in the switches etc ****

3) Verify that the Network Interface Card (NIC) is compatible and working

properly. Refer to

< http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tec

h_note09186a00800a7af0.shtml>

http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tech

_note09186a00800a7af0.shtml

**** N/A switch to switch connectivity ****

4) Verify that the flow control settings are the same on both sides of a

Ethernet link.

Here are the flow control settings:

FlowControl on 2960:

show flowcontrol interface gigabitEthernet 0/45

Port       Send FlowControl  Receive FlowControl  RxPause TxPause

           admin    oper     admin    oper

---------  -------- -------- -------- --------    ------- -------

Gi0/45     Unsupp.  Unsupp.  off      off         0       0

show flowcontrol interface gigabitEthernet 0/46

Port       Send FlowControl  Receive FlowControl  RxPause TxPause

           admin    oper     admin    oper

---------  -------- -------- -------- --------    ------- -------

Gi0/46     Unsupp.  Unsupp.  off      off         0       0

Flow Control on 4948E:

show flowcontrol interface gi1/35

Port       Send FlowControl  Receive FlowControl  RxPause TxPause

           admin    oper     admin    oper

---------  -------- -------- -------- --------    ------- -------

Gi1/35     on       disagree desired  off         0       0

show flowcontrol interface gi1/36

Port       Send FlowControl  Receive FlowControl  RxPause TxPause

           admin    oper     admin    oper

---------  -------- -------- -------- --------    ------- -------

Gi1/36     on       disagree desired  off         0       0

[paolo bevilacqua]

The drop ratio is very small, about 1 each 120,000. So there is really nothig to worry about.