Output Queue Drops

[Vianney]

Hi,

I have output queue drops on some of the 4506 Interfaces that i can't explain ...
any idea where i can start the search ?

i've searched at cisco and the "output queue troubleshooting" document doesn't seems to help...

The architecture is :

5 floors, only one VLAN, 2 switches per floor 2950+3500 G-stacked

Each 3500 trunked to the 4506 => port channels

we had an analisys tool on the network, which was on the monitor port (SPAN) on the 4506 and had millions of output pack drops, so i did shutdown its port to see if it couldn't be the problem...

I cleared counters and waited, the drops seems to have disapeared , but no ... they're still here ...

Some users complains about network disconnections sometimes.

any ideas ?

 

[vipergg]

The output drops are probably from oversubscribing the span port if you did a span of the whole vlan to the analysis tool and would not contribute to any of the problems you may be seeing , it is just the switch doing it's job of dropping the packets when the interface runs out of buffers . If you have more than say 250 users on this vlan you should think about breaking it up into multiple subnets to decrease your braodcast domain. The disconnects could be almost anything . I would certainly check all your speed/duplex settings for the switch to switch connections and any users that may be complaing first. If you have a lot of interfaces with output drops then you would have to go to the users and see what they are transferring across the network , it takes a lot to fill a 100 meg full duplex pipe and also verify their nic settings against the switch settings they are attached to.

 

[Vianney]

well i've done more test since earlier, and i found a way to reproduce the probleme ...

on the 4506 switch i plugged a workstation
a file server is plugged in the same switch

i move a file (700Mb) from the workstation to the file server (while pinging the file server): no problem

i move a file (700Mb) from the fileserver to the workstation while pinging the file server : the ping starts to "delay passed" and comes back and so on, from time to time
and the output packet drops increased in the workstation's port of the switch ...

interface GigabitEthernet4/26
speed 100
duplex full
spanning-tree portfast


here's the conf of the workstation port ..

nothing weird ...
the workstation nic is set to 100 full too.

i'm clueless :s

 

[vipergg]

Can you post a "show interface counters errors" and maybe we can see something .

 

[Yick]

Any way there could be 1Gb port sending data to 100Mb port and droping packets ?

Cisco bug ?

 

[Yick]

check this ?

http://www.netadmintools.com/art426.html

 

[Vianney]

Port InBytes InUcastPkts InMcastPkts InBcastPkts
Gi4/26 5623509290 8663127 6 374

Port OutBytes OutUcastPkts OutMcastPkts OutBcastPkts
Gi4/26 14642039430 11608185 58828 571396

GigabitEthernet4/26 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet Port, address is

MTU 1500 bytes, BW 100000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, link type is auto, media type is 10/100/1000-TX
input flow-control is off, output flow-control is off
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output never, output hang never
Last clearing of "show interface" counters 1d00h
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 2828
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 1000 bits/sec, 1 packets/sec
5 minute output rate 7000 bits/sec, 8 packets/sec
8663598 packets input, 5623528768 bytes, 0 no buffer
Received 381 broadcasts (6 multicast)
0 runts, 0 giants, 0 throttles
2 input errors, 2 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
12238876 packets output, 14642135228 bytes, 0 underruns
1270 output errors, 8 collisions, 0 interface resets
0 babbles, 1270 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out