Getting Total Output drops

[rakesh.dutt]

Hi,

We are seeing the total output drops in the WAN interface & we are seeing the drops in ping of remote ip address .  Show interface of WAN ip is below;

Can anybody please help me understand the reason for the same. The link is also not over utilised & hence there should not be any congestion ob the link.

  sh int g0/1  

  GigabitEthernet0/1 is up, line protocol is up

  Hardware is BCM1125 Internal MAC, address is 0016.c79b.8e91 (bia 0016.c79b.8e91)

  Internet address is 10.97.129.206/30

  MTU 1500 bytes, BW 8000 Kbit, DLY 100 usec,

     reliability 255/255, txload 13/255, rxload 69/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex, 100Mb/s, media type is RJ45

  output flow-control is XON, input flow-control is XON

  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 6d11h

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 7806

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  30 second input rate 2169000 bits/sec, 425 packets/sec

  30 second output rate 414000 bits/sec, 360 packets/sec

     226672614 packets input, 1869297052 bytes, 0 no buffer

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

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

     0 watchdog, 130010 multicast, 0 pause input

     0 input packets with dribble condition detected

     201540346 packets output, 3620486442 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

Regards,

Rakesh

[Mohamed Sobair]

Rakesh,

The reason of Output drops is either, a Congested Interface OR duplex mismatch.  If you have an Interface operating in half duplex mode, its recommended to be changed to a Full duplex mode, if you have a congested interface (Congestion may occur on different time intervals depend on the traffic utilization , not necessarily be the time when you took the output of (show interface x/y), then its recommended to apply QoS Congestion Managment and Avoidance mechanisms.

Regards,

Mohamed

[Joseph W. Doherty]

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Posting

Your output drops are likely due to transient congestion.  Note the ratio of drops to transmitted packets.

For 100 Mbps WANs, the default queue of 40 is likely too shallow.  You might try setting queue depth to handle half of BDP.

As to your ping drops, this interface's stats doesn't seem to imply that they are happening on egress.  However, you didn't post the other side's stats.  Nor did you describe the WAN technology and topology.  Is it a multipoint connection and/or does provider offer less then physical link bandwidth?

[rakesh.dutt]

Hi Josep,

This is an Metro ethernet link & the bandwidth of the link is 8Mb.

below is the configuration of the interface:

interface GigabitEthernet0/1

bandwidth 8000

ip address 10.97.129.206 255.255.255.252

load-interval 30

duplex full

speed 100

media-type rj45

negotiation auto interface

Regards,

Rakesh

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Ah, that may help!

Since we see some drops running at 100 Mbps, very likely you're on occasion exceeding 8 Mbps provided by your Metro Ethernet vendor; they will often drop the excess.

Trying shaping to 8 Mbps (or 5-15% slower to allow for Ethernet L2 overhead).