we have c3850 trunk with other switch 4948 and its LACP 4x1G interface bonding (etherchannel) out of 4 1G we are getting Total output drops
on 2 interface.
This is all started yesterday when i upgrade software on this switch before that everything was good. doesn't make sense. I have done this upgrade on other switches to but no issue so far.
C3850#sh int g2/0/1
GigabitEthernet2/0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 1c1d.86a9.3501 (bia 1c1d.86a9.3501)
Description: coreSW_1_W_1of4_p
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 36/255, rxload 25/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/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 00:00:11, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 133157273
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 100659000 bits/sec, 61038 packets/sec
5 minute output rate 144390000 bits/sec, 76852 packets/sec
3445318149 packets input, 715126259616 bytes, 0 no buffer
Received 827824 broadcasts (666658 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 666658 multicast, 0 pause input
0 input packets with dribble condition detected
4521665906 packets output, 1080744400610 bytes, 0 underruns
133157273 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
Counter:
C3850#sh int g2/0/1 counters
Port InOctets InUcastPkts InMcastPkts InBcastPkts
Gi2/0/1 718020111847 3459023952 668522 161527
Port OutOctets OutUcastPkts OutMcastPkts OutBcastPkts
Gi2/0/1 1084965964251 4539489816 109940 86365
Stats:
C3850#sh int g2/0/1 stats
GigabitEthernet2/0/1
Switching path Pkts In Chars In Pkts Out Chars Out
Processor 10458 2249522 0 0
Route cache 0 0 18985 2870366
Total 10458 2249522 18985 2870366
EDIT:
Our total utilization on link is 400Mbps, and i am seeing all link using around ~100 Mbps individually (few bytes here and there).
I am not seeing any performance issue on network. this trunk is connected to other switch and they are also running same speed interface 4x1G. I have upgrade multiple switch with same software and they all working fine without any interface error.
Best Answer
Have you noticed a degradation in performance since doing the upgrade? If not, the issue could be that you have been experiencing the issue all along but your previous IOS version wasn't reporting the errors.
let's say you are experiencing a degradation in performance though. As you're seeing output drops this typically means that the links are experiencing congestion.
As you might already know, traffic is not equally split across all links in a port channel. For example, port channeling 4 x 1Gb links does not guarantee you 4Gb of throughput. The traffic is split across the links depending on what hashing algorithm you're using. Given this, it actually possible for one link to be maxed out while the other links remain dormant.
While we're on the topic of load balancing algorithms, the issue your experiencing could be related to CEF polarization.
Another possible cause is micro bursting which happens when you've got a speed step down (e.g a 1Gb interface connected to a 100Mb interface). If your interfaces are configured to auto negotiate their speed and duplex, check them all to ensure that they've negotiated their settings correctly.