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3750 output drops at exact multiples of 78

BrettCurtis5442
Beginner
Beginner

I've got a 3750 switch that's being flagged in solarwinds for discards.  This is a distribution switch with gig ports, and its single uplink port to a Riverbed and satellite wan link is the one recording drops.  It's average utilization is a pretty consistent 300K.  There's no QoS configured, just a basic trunk configuration.

First question, what is the time interval on the sh int output drops stat?  Every time I display it, it's a multiple of exactly 78.

Second question:  It's weird that it's exactly 78 bytes or an exact multiple of 78.  Anyone have any ideas why that is?

 

sh int gi1/0/1
GigabitEthernet1/0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 7c69.f6f1.9981 (bia 7c69.f6f1.9981)
Description:
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 1000Mb/s, link type is auto, media type is 10/100/1000BaseTX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:31, output 00:00:35, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 78
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 307000 bits/sec, 87 packets/sec
5 minute output rate 275000 bits/sec, 77 packets/sec
5288829618 packets input, 2283416132780 bytes, 0 no buffer
Received 126878804 broadcasts (54084452 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 54084452 multicast, 0 pause input
0 input packets with dribble condition detected
8516447191 packets output, 9289365956118 bytes, 0 underruns
0 output errors, 0 collisions, 3 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

 

Hitting the show interface several times in a row:

Total output drops: 156

Total output drops: 234

Total output drops: 234

Total output drops: 78

Total output drops: 78

Total output drops: 156

etc, all day

 

4 Replies 4

BrettCurtis5442
Beginner
Beginner

Actually it's happening on ten interfaces.

5 minute input rate 2290000 bits/sec, 315 packets/sec
5 minute output rate 889000 bits/sec, 292 packets/sec

Total output drops: 6215

Total output drops: 12430

Total output drops: 18645

 

5 minute input rate 21000 bits/sec, 3 packets/sec
5 minute output rate 29000 bits/sec, 32 packets/sec

Total output drops: 7297

Total output drops: 14594 (@0/18000b/s in/out)

 

5 minute input rate 1000 bits/sec, 2 packets/sec
5 minute output rate 25000 bits/sec, 25 packets/sec

Total output drops: 7304

Total output drops: 14608

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master
What IOS are you running?

The 3750 is a bit infamous for drops due to it only having 4 MB RAM per 24 copper ports or its uplink ports. If QoS is enabled, and running defaults, often you see higher drops than with QoS totally disabled. However, often the least number of drops is with QoS enabled and configured for your needs.

That said, 78 drops out of 8,516,447,191 is usually not a cause for concern. Traditionally, you need to be concerned only when drop rate exceeds 1%.