Output/input queue drops

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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Calin Chiorean Tue, 09/23/2008 - 01:53

Hello!

One card queue is smaller than the other one. As I see there is a lot of traffic on the interface so, the lower queue size is dropping packets as he has not room for them. This is a usual problem that I saw mostly when connection an old card to a new server which support a high throughput and is having a lot of traffic. In my case the solution was to replace the hardware.

Maybe somebody has a different approach for this issue?

Cheers,

Calin

Joseph W. Doherty Tue, 09/23/2008 - 03:59

Input queue drops usually indicate the device couldn't process the input stream fast enough, and sometimes requires analysis and effort to elminate.

Output queue drops usually indicate (transient) congestion, and for such, is quite normal.

Since you only had 33 input drops for 35,908,851 packets input, it shouldn't be of concern.

You had 58,350 output drops for 35,645,315 packets output, which isn't real bad at about .16%. For gig speed on a LAN, and allowing for a BDP based on about 1 ms latency, you could pretty safely double your output queue size to 80 and see if that decreases your drop percentage.

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