input/output queue

Unanswered Question
Sep 23rd, 2008

DOH-GSR-PE2#sh int g2/0/1 controller

GigabitEthernet2/0/1 is up, line protocol is up

Hardware is GigabitEthernet, address is 0019.55e9.f4cd (bia 0019.55e9.f4cd)

Description: ***Connected to OLD_4500-Gig4/47***

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, rely 255/255, load 34/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full Duplex, 1000Mbps, link type is force-up, media type is LX

output flow-control is on, input flow-control is on

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters 00:22:24

Queueing strategy: fifo

Output queue 0/40, 58350 drops; input queue 1/75, 33 drops

Available Bandwidth 1000000 kilobits/sec

5 minute input rate 115415000 bits/sec, 28397 packets/sec

5 minute output rate 134713000 bits/sec, 27906 packets/sec

35908851 packets input, 17612788274 bytes, 0 no buffer

Received 28758 broadcasts, 0 runts, 4518126 giants, 0 throttles

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

0 watchdog, 67269 multicast, 0 pause input

35645315 packets output, 21985400017 bytes, 0 underruns

Transmitted 2596 broadcasts

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

Above is the output of show interface command. In the output we see some output queue drops with very less queue.

Output queue 0/40, 58350 drops; input queue 1/75, 33 drops

What could be the reason for this act?

I have this problem too.
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Istvan_Rabai Tue, 10/21/2008 - 09:22

Hi Senthilkumar,

The reason for these output queue drops is that there were several congestions earlier on the output queue.

The default queueing strategy for Gig interfaces is FIFO, which means First In First Out.

Output queue 0/40 means that the FIFO queue size is 40 packets (40 packets can be stored in the FIFO queue). If there is congestion and more than 40 packets try to go out of interface Gig2/0/1, then the packets above 40 cannot be stored as there is no memory allocated for them.

Depending on your traffic patterns there can be several solutions to this.

One solution may be to increase the FIFO queue size using the hold-queue x interface config command, where x is the number of packets. But this cannot always solve the problem.

Another solution could be to use some other queuing strategy like Weighted Round Robin with priority queueing.

You should look at QoS possibilities in the product documentation of your switch on cisco.com.

Each type has some specifics for configuring QoS.

Cheers:

Istvan

hkj0516 Wed, 10/29/2008 - 01:29

I have a same problem for this case.

So, I was using the hold-queue x command to change from 40 to 200 packets. But it's still have drop on the output queue.

I will to configuration other QoS on the Gigaethernet.

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