[c-nsp] Unexplainable Output drops on serial interfaces

[David Freedman]

Todd, do you have any kind of shaping / QoS on these circuits?

Drops by traffic management configurations are frequently shown as
interface drops.

Dave.


Todd Shipway wrote:
> Hi,
> 
> We have multiple T1 interfaces across different cards and different type
> of cards in a 7513.  Many interfaces are showing output drops and I
> can't pinpoint why.  The interfaces are spread throughout the system and
> I can't pinpoint a single point that could be causing the drops.  Below
> is 2 interfaces showing the drops.
> 
> The bandwidth is very low when the drops are occurring, these 2
> interfaces are part of a multilink interface which shows no drops.  Any
> ideas as to what I should look for that could be causing this?
> 
> Serial9/0/0:12 is up, line protocol is up 
>   Hardware is cyBus T3
>   Description: Bonded T1
>   MTU 1500 bytes, BW 1540 Kbit, DLY 20000 usec, 
>      reliability 255/255, txload 11/255, rxload 5/255
>   Encapsulation PPP, LCP Open, multilink Open
>   Link is a member of Multilink bundle Multilink66, crc 16, loopback not
> set
>   Keepalive set (10 sec)
>   Last input 00:00:00, output 00:00:00, output hang never
>   Last clearing of "show interface" counters 6d03h
>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:
> 4050
>   Queueing strategy: fifo
>   Output queue: 0/100 (size/max)
>   5 minute input rate 33000 bits/sec, 19 packets/sec
>   5 minute output rate 68000 bits/sec, 18 packets/sec
>      3121597 packets input, 667733893 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 abort
>      2929740 packets output, 1363133541 bytes, 0 underruns
>      0 output errors, 0 collisions, 0 interface resets
>      0 output buffer failures, 0 output buffers swapped out
>      0 carrier transitions no alarm present
>   Timeslot(s) Used: 1-24, Transmitter delay is 0 flags
>   non-inverted data
> 
> Serial9/0/0:11 is up, line protocol is up 
>   Hardware is cyBus T3
>   Description: Bonded T1
>   MTU 1500 bytes, BW 1540 Kbit, DLY 20000 usec, 
>      reliability 255/255, txload 10/255, rxload 5/255
>   Encapsulation PPP, LCP Open, multilink Open
>   Link is a member of Multilink bundle Multilink66, crc 16, loopback not
> set
>   Keepalive set (10 sec)
>   Last input 00:00:00, output 00:00:00, output hang never
>   Last clearing of "show interface" counters 6d03h
>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:
> 4085
>   Queueing strategy: fifo
>   Output queue: 0/100 (size/max)
>   5 minute input rate 31000 bits/sec, 19 packets/sec
>   5 minute output rate 65000 bits/sec, 17 packets/sec
>      3122847 packets input, 668516220 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 abort
>      2930011 packets output, 1364226428 bytes, 0 underruns
>      0 output errors, 0 collisions, 0 interface resets
>      0 output buffer failures, 0 output buffers swapped out
>      0 carrier transitions no alarm present
>   Timeslot(s) Used: 1-24, Transmitter delay is 0 flags
>   non-inverted data
> 
> Multilink interface for the T1's above:
> Multilink66 is up, line protocol is up 
>   Hardware is multilink group interface
>   Description: Bonded T1
>   Internet address is 10.10.56.1/30
>   MTU 1500 bytes, BW 3080 Kbit, DLY 100000 usec, 
>      reliability 255/255, txload 11/255, rxload 4/255
>   Encapsulation PPP, LCP Open, multilink Open
>   Open: IPCP, loopback not set
>   Keepalive set (10 sec)
>   DTR is pulsed for 2 seconds on reset
>   Last input 00:00:30, output never, output hang never
>   Last clearing of "show interface" counters 1w0d
>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
>   Queueing strategy: Class-based queueing
>   Output queue: 0/40 (size/max)
>   5 minute input rate 58000 bits/sec, 47 packets/sec
>   5 minute output rate 139000 bits/sec, 49 packets/sec
>      7075294 packets input, 1705142684 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 abort
>      7483773 packets output, 3524642362 bytes, 0 underruns
>      0 output errors, 0 collisions, 0 interface resets
>      0 output buffer failures, 0 output buffers swapped out
>      0 carrier transitions
> 
> Any help would be appreciated.  As I said earlier, this scenario is
> happening on multiple interfaces throughout the system.  A Channelized
> DS3 card has been swapped out as a test as well as the output queue
> raised from 40 to 100 with no change in drops.
> 
> -Todd
> 
> 
> 
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> 
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