Dropping packets

[ahmed.benabdalla9]

I see on one side on the interface on Datacenter this :

is the diiferent interface BW cause packet drops ? 

8 zeros BW 

MTU 9000 bytes, BW 100000000 Kbit (Max: 100000000 Kbit)  

2976014606 packets input, 3234640147216 bytes, 82 total input drops
0 drops for unrecognized upper-level protocol
Received 30 broadcast packets, 185339 multicast packets
3260269016 packets output, 4069142810851 bytes, 12874401 total output drops
Output 51 broadcast packets, 701461 multicast packets

on the other side the cell side interface :

7 zers on BW

MTU 9000 bytes, BW 10000000 Kbit (Max: 10000000 Kbit)  

3149737804 packets output, 3252555524216 bytes, 0 total output drops
Output 609 broadcast packets, 996063 multicast packets
0 output errors, 0 underruns, 0 applique, 0 resets
0 output buffer failures, 0 output buffers swapped out

[Reza Sharifi]

It is possible that this is happening because of interface mismatch:

• When too much traffic is sent out of a single interface, the buffers for that interface can become overwhelmed and output drops occur. An interface with too few buffers can also increase the probability of output drops.
• Output drops can also be caused by a mismatch between the speed of the interface and the speed of the connected device. For example, if a 10 Gbps interface is connected to a device that only supports a data transfer rate of 1 Gbps, the interface can drop packets if it is unable to slow down the data rate to match the capabilities of the device.
• https://www.cisco.com/c/en/us/support/docs/switches/catalyst-9600-series-switches/220491-understand-output-drops-on-high-speed-in.html#:~:text=An%20interface%20with%20too%20few,speed%20of%20the%20connected%20device.
• HTH

[Joseph W. Doherty]

Just a side note . . .

@Reza Sharifi's Cisco TechNote reference contains lots of good information and, IMO, not so good information.  Unfortunately, without a deep understanding of QoS, it can be very difficult to tell the difference between good vs. not so good information.

As just one example, after that TechNote explains microburstimg happens down in the millisecond range, and is generally not visible across longer periods, even 30 seconds, we also find:

Total output drops: 299040207
Total output bytes: 5930422327799

Percentage of output drops = 299040207/5930422327799 x 100 = 0.005%

In this example, the total output drops represent 0.005% of the total amount of bytes transmitted on this interface in the past six weeks (last clearing of counters 6w1d).

• The total number of packets versus number dropped is minor, and should not have any impact.

We don't have a drop rate issue, because the drop percentage is so low over a 6w1d period.  IMO maybe, maybe not!

[Joseph W. Doherty]

Insufficient information.  In general, interface BW is a logical setting which usually has no direct control over transmission rate, for either ingress or egress.

As @Reza Sharifi correctly noted, the most common cause of egress drops is running out of egress buffer resources but how best to mitigate depends on cause and your network goals (which may include such drops are acceptable).