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Beginner

Output drops on Cisco 2960G switch

I'm seeing output drops, but I don't see any apparent issue. Looks like it's increasing by 10 - 15 packets per second. The interface is connected to a gig Ethernet link.

 

SWITCH-2960G#sh int gi0/9
GigabitEthernet0/9 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 64d9.895e.4389 (bia 64d9.895e.4389)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 62/255, rxload 62/255
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 00:00:13, output 00:00:00, output hang never
Last clearing of "show interface" counters 19:25:54
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 5597
Queueing strategy: fifo
Output queue: 0/40 (size/max)
30 second input rate 246471000 bits/sec, 26253 packets/sec
30 second output rate 246767000 bits/sec, 26279 packets/sec
199181745 packets input, 163153601557 bytes, 0 no buffer
Received 767965 broadcasts (705093 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 705093 multicast, 0 pause input
0 input packets with dribble condition detected
119496823 packets output, 122753976025 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
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
SWITCH-2960G#

 

SWITCH-2960G#sh buffers | i no[ ]memory
0 failures (0 no memory)
0 failures (0 no memory)
0 failures (0 no memory)
0 failures (0 no memory)
0 failures (0 no memory)
0 failures (0 no memory)
0 failures (0 no memory)
0 failures (0 no memory)
SWITCH-2960G#

 

This is a 2960G switch with 32 Gbps of switching fabric, so capacity shouldn't be an issue passing 250 Mbps in each direction over this port, right?

Everyone's tags (1)
6 REPLIES 6
VIP Expert

Re: Output drops on Cisco 2960G switch

30 second input rate 246471000 bits/sec, 26253 packets/sec
30 second output rate 246767000 bits/sec, 26279 packets/sec

It is 245 Mbps. So, the number of output drops are very small (5597). If it is not causing any application issues, you should be fine.

HTH

VIP Expert

Re: Output drops on Cisco 2960G switch

". . . so capacity shouldn't be an issue passing 250 Mbps in each direction over this port, right?"

Maybe, maybe not. That's a 30 second average. Drops can happen during a microburst.
Beginner

Re: Output drops on Cisco 2960G switch

Ah, okay. Are there any practical ways to detect them?

VIP Expert

Re: Output drops on Cisco 2960G switch

You can try and SPAN the port and connect a Wireshark to another port on the switch and analyze the data you capture. 

HTH

Beginner

Re: Output drops on Cisco 2960G switch

Sure, I can do that. What should I be on the lookout for in the captured data?

VIP Expert

Re: Output drops on Cisco 2960G switch

You would have to create a filter in Wireshark to look for drop frames, re-transmission, etc..

You can start with this link:

https://www.comparitech.com/net-admin/how-to-use-wireshark/#How_to_Capture_Data_Packets

HTH

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