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Output drops thought QOS disaled in 3750 switch

rkbalaguru
Level 1
Level 1

Hi All,

 

We are using Cisco 3750 switch where we have configured one port as SPAN port . The port is generating lot of output drops even we have QOS disabled glogablly, other ports are fine. We can see the traffic on the tool connected in the SPAN port. Since we did not configure QOS, i did not think of increasing buffer, what could be other cause of the output drops, could you share some idea how to fix it?

7 Replies 7

Hello,

 

post the output of 'show interfaces x' where X is the interface that experiences the drops...

Please check the below output,

 

GigabitEthernet1/0/14 is up, line protocol is down (monitoring)
Hardware is Gigabit Ethernet, address is 2834.a220.678e (bia 2834.a220.678e)
Description: SPAN
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 4/255, rxload 1/255
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 never, output 02:39:29, output hang never
Last clearing of "show interface" counters 01:01:29
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 281883
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 18208000 bits/sec, 3030 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
10674960 packets output, 7867741738 bytes, 0 underruns
0 output errors, 0 collisions, 0 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

Hello,

 

turn flowcontrol on on the interface (flowcontrol receive on) and check if that makes a difference...

I just tried it but still an output drops increasing,

 

GigabitEthernet1/0/14 is up, line protocol is down (monitoring)
Hardware is Gigabit Ethernet, address is 2834.a220.678e (bia 2834.a220.678e)
Description: SPAN
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 3/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
input flow-control is on, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:05:18, output hang never
Last clearing of "show interface" counters 00:04:54
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 8374
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 13103000 bits/sec, 2360 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected

 

 

There is something wrong with the downstream client. "0 packets input:"?

We have configured this interface as SPAN port, so this SPAN port connected to Gigamon TAP device which will send mirrored traffic to Netscout for packet analysis. When i look at Netscout we see the vlans sent from SPAN session created in 3750 switch and see the packet aswell. 

Moreover there is no much configuration on Gigamon which will receive network traffic from SPAN port and send it to Netcout connect tool port. So i am not able to identify what could be an issue

Joseph W. Doherty
Hall of Fame
Hall of Fame
Disabling 3750 QoS doesn't always avoid all egress drops. Often with QoS disabled, you'll have less egress drops than you would with a default QoS configuration, but I've often found the "best" configuration for avoiding 3750 egress drops is often a custom QoS configuration.
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