Network administrators at times face the challenge of output drops which causes data traffic loss. Output drops are generally caused by congested interfaces and best possible option to address this situation is to look into increasing the speed of that link. Other factors may also be responsible for causing output drops on interfaces.
Some of common causes of output drops on interface are enlisted below –
- Bad cable
- Oversubscription on the port or module
- Speed/Duplex mismatch.
Sometime overall traffic utilization may be showing low, however traffic bursts under “show interface” may not be giving clear picture. The default output rate is 5 minutes which may miss the bursty traffic. One option is to shorten the load interval from the default 5 minutes to 30 seconds using the interface-level command of “load-interval 30”.
Some of other Troubleshooting methods include –
- Using wireshark for detailed understanding of output drops.
- Increasing queue-limit
- Increasing hold queue
Infact following list of command can be very useful in troubleshooting output drops on interface –
- show interfaces switching
- show interfaces stats
- ip accounting mac-address
- show interfaces mac-accountin
- sh int <int no> | include drop
Below is the output of “show interface” command to show output drops as under –
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:24, output never, output hang never
Last clearing of “show interface” counters 02:55:56
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 413678
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 64000 bits/sec, 32 packets/sec
765432 packets input, 84505586 bytes, 0 no buffer
Received 4508 broadcasts (4009 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 4009 multicast, 0 pause input
0 input packets with dribble condition detected
765432 packets output, 84505586 bytes, 0 underruns
527779 output errors, 0 collisions, 1 interface resets
0 unknown protocol drops
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
ABOUT THE AUTHOR
I am here to share my knowledge and experience in the field of networking with the goal being – “The more you share, the more you learn.”
I am a biotechnologist by qualification and a Network Enthusiast by interest. I developed interest in networking being in the company of a passionate Network Professional, my husband.
I am a strong believer of the fact that “learning is a constant process of discovering yourself.”
– Rashmi Bhardwaj (Author/Editor)
