how to reduce total output drops

Answered Question
May 13th, 2008
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we have connection between 6509 switch interface and 3725 access device. however on output drops are increasing 6509 interface, any ideas how can i make to zero. below are sh int output for both device.

6509-CORE-1-1#sh int gi3/2


GigabitEthernet3/2 is up, line protocol is up (connected)


Hardware is C6k 1000Mb 802.3, address is 0015.2bb1.87d9 (bia 0015.2bb1.87d9)


Description: ::ge3/2::oper::3725-ACCESS-1-1::fa0/0::100M


MTU 1500 bytes, BW 100000 Kbit, DLY 10 usec,


reliability 255/255, txload 17/255, rxload 1/255


Encapsulation ARPA, loopback not set


Keepalive set (10 sec)


Full-duplex, 100Mb/s


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


Clock mode is auto


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


Last input 00:00:33, output 00:00:02, output hang never


Last clearing of "show interface" counters 00:36:44


Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 4417


Queueing strategy: fifo


Output queue: 0/40 (size/max)


5 minute input rate 6000 bits/sec, 5 packets/sec


5 minute output rate 7013000 bits/sec, 1561 packets/sec


12989 packets input, 2170281 bytes, 0 no buffer


Received 993 broadcasts (993 multicasts)


0 runts, 0 giants, 0 throttles


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


0 watchdog, 0 multicast, 0 pause input


0 input packets with dribble condition detected


3523848 packets output, 1963109904 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






3725-ACCESS-1-1#sh int fa0/0


FastEthernet0/0 is up, line protocol is up


Hardware is Gt96k FE, address is 0011.9267.d7c0 (bia 0011.9267.d7c0)


Description: ::fa0/0::oper::6509-CORE-1-1::ge3/2::100M


Internet address is 10.200.0.5/24


MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,


reliability 255/255, txload 1/255, rxload 1/255


Encapsulation 802.1Q Virtual LAN, Vlan ID 1., loopback not set


Keepalive set (10 sec)


Full-duplex, 100Mb/s, 100BaseTX/FX


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 4w5d


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


Queueing strategy: fifo


Output queue: 0/40 (size/max)


5 minute input rate 10000 bits/sec, 9 packets/sec


5 minute output rate 9000 bits/sec, 7 packets/sec


160141872 packets input, 3554767197 bytes


Received 4856018 broadcasts, 0 runts, 0 giants, 0 throttles


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


0 watchdog


0 input packets with dribble condition detected


154246689 packets output, 3477017281 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 output buffer failures, 0 output buffers swapped out




Correct Answer by Kevin Dorrell about 8 years 10 months ago

I don't think there is much you can do about it. You have averaged 7 Mbps over the last 5 minutes, and it would be a pretty fair bet that from time to time you are going over the 100 Mbps on peaks. At that point the interface is congested, and will drop packets as soon as the output queue is full.


If the drops are disrupting any applications, you can manage the congestion by giving priority to the sensitive applications. That opens the QoS can of worms.


If you need a quick and easy fix, it is to upgrade the link to Gbit. That would at least defer the problem, but it might give you another problem downstream.


I know the drops don't look good, but if they are not upsetting any applications then they do no harm. You could simply let them happen, and keep an eye on it. Otherwise, manage them.


Kevin Dorrell

Luxembourg


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bvsnarayana03 Tue, 05/13/2008 - 23:17
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These drops must be due to the hardware queuing but doesnt matter compared to the output rate on interface. It would have been bothering when there were errors on interface or CRC.

roger.malik Tue, 05/13/2008 - 23:44
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i can see no CRC errors currently but still output drops are increasing, kindly suggest

roger.malik Wed, 05/14/2008 - 01:04
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hi guys any ideas on this ? what should i check to troubleshoot

Correct Answer
Kevin Dorrell Wed, 05/14/2008 - 03:36
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I don't think there is much you can do about it. You have averaged 7 Mbps over the last 5 minutes, and it would be a pretty fair bet that from time to time you are going over the 100 Mbps on peaks. At that point the interface is congested, and will drop packets as soon as the output queue is full.


If the drops are disrupting any applications, you can manage the congestion by giving priority to the sensitive applications. That opens the QoS can of worms.


If you need a quick and easy fix, it is to upgrade the link to Gbit. That would at least defer the problem, but it might give you another problem downstream.


I know the drops don't look good, but if they are not upsetting any applications then they do no harm. You could simply let them happen, and keep an eye on it. Otherwise, manage them.


Kevin Dorrell

Luxembourg


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