how to verify that switch is dropping packets ?

[ITexpert]

Hello Guys,

@Richard Burts @Joseph W. Doherty  @Reza Sharifi @Deepak Kumar @paul driver   @Georg Pauwen 

I am using cisco 4506 series,

Is there any way in real-time that i can see that trunk port is going through congestion and dropping is happening.

I have the source IP or mac  of device and destination Ip or mac .

Thanks

[O Bitar · Accepted solution]

Hi ITExpert

  when you say drops in real-time that still means drops per seconds or minutes. So repitative show interface should do that  enough although not practical. You other obvious option is to rely on SNMP and the you will have historical data as frequent as you pull the interface for data. I do not know of anyway to find drops against specific IP or MAC address.

Regards

Omar

[Joseph W. Doherty]

Interface stats should record the drops. As Omar notes, these might obtained by SNMP polling.

It also might be possible, using something like RMON or EEM to "alarm/trap" if drops exceed a certain amount during a time period. The advantage of some form of local device monitoring, you don't need to keep querying the device avoiding the "old joke" issue of finding high CPU and high interface utilization are caused by SNMP polling.

[ITexpert]

Hello Guys,

@O Bitar @Joseph W. Doherty

According to this sh interface output  what will be my drop count .

1108-CORE-01# sh interfaces g3/27
GigabitEthernet3/27 is up, line protocol is up (connected)
Hardware is C6k 1000Mb 802.3, address is 0027.0d96.1456 (bia 0027.0d96.1456)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 4/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, media type is SX
input flow-control is off, output flow-control is on
Clock mode is auto
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:17, output 00:00:22, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 22784
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 18174000 bits/sec, 1635 packets/sec
5 minute output rate 987000 bits/sec, 874 packets/sec
7857516737 packets input, 11024972887275 bytes, 0 no buffer
Received 11266737 broadcasts (9893246 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
13300922508 packets output, 1395625325162 bytes, 0 underruns
0 output errors, 0 collisions, 3 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

[O Bitar]

Hi

   Total output drops: 22784

BR

Omar

[ITexpert]

hello @O Bitar @Joseph W. Doherty

why this number is always same then ?  it should refresh?

I refresh the command  many times?

Thanks  

[Joseph W. Doherty · Accepted solution]

Yes it should refresh with every show interface invocation. If it's not changing, it should mean you've haven't had any additional drops since your last invocation of the show interface command.

However, on some switches, the interface drop counter doesn't always reflect drops at the hardware level. If that's a case, you then need to issue other commands to see those drops.

[ITexpert]

Hello @Joseph W. Doherty

Please refer other commands as well.

Thanks

[Joseph W. Doherty]

Ok, for example, on a 3750 you might issue:
show mls qos int g#/#/# statist