How can I check if Cisco switch (2960) does loose packets (e.g. because of congestion)?
What are tools/commands for troubleshooting such issues?
2 Answers
Both the show int and show int summary commands should give you enough information to at least see if you are having problems on a particular port.
The show int summary command will give you an overview of each interface's input/output hold queue as well as the current bits and packets per second counts and the number of packets dropped from the input/output queues.
#show int summary
*: interface is up
IHQ: pkts in input hold queue IQD: pkts dropped from input queue
OHQ: pkts in output hold queue OQD: pkts dropped from output queue
RXBS: rx rate (bits/sec) RXPS: rx rate (pkts/sec)
TXBS: tx rate (bits/sec) TXPS: tx rate (pkts/sec)
TRTL: throttle count
Interface IHQ IQD OHQ OQD RXBS RXPS TXBS TXPS TRTL
-----------------------------------------------------------------------------------------------------------------
Vlan1 0 0 0 0 0 0 0 0 0
* Vlan2 1 0 0 0 6000 8 6000 4 0
FastEthernet0 0 0 0 0 0 0 0 0 0
GigabitEthernet1/0/1 0 0 0 0 0 0 0 0 0
GigabitEthernet1/0/2 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/3 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/4 0 0 0 0 9000 4 190000 19 0
* GigabitEthernet1/0/5 0 0 0 0 3000 2 36000 15 0
* GigabitEthernet1/0/6 0 0 0 0 3000 2 17000 13 0
GigabitEthernet1/0/7 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/8 0 0 0 0 114000 7 196000 30 0
* GigabitEthernet1/0/9 0 0 0 0 136000 32 270000 43 0
* GigabitEthernet1/0/10 0 0 0 0 7000 8 254000 27 0
GigabitEthernet1/0/11 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/12 0 0 0 0 0 0 12000 11 0
* GigabitEthernet1/0/13 0 0 0 15 1000 0 16000 13 0
* GigabitEthernet1/0/14 0 0 0 0 1000 1 13000 12 0
* GigabitEthernet1/0/15 0 0 0 0 1000 1 14000 12 0
GigabitEthernet1/0/16 0 0 0 0 0 0 36000 6 0
* GigabitEthernet1/0/17 0 0 0 0 8000 10 35000 43 0
GigabitEthernet1/0/18 0 0 0 0 0 0 0 0 0
GigabitEthernet1/0/19 0 0 0 0 0 0 0 0 0
GigabitEthernet1/0/20 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/21 0 0 0 0 23000 32 20000 22 0
* GigabitEthernet1/0/22 0 0 0 0 0 0 12000 11 0
* GigabitEthernet1/0/23 0 0 0 0 0 0 12000 11 0
GigabitEthernet1/0/24 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/25 0 0 0 0 0 0 78000 11 0
* GigabitEthernet1/0/26 0 0 0 0 0 0 12000 11 0
* GigabitEthernet1/0/27 0 0 0 0 7000 4 215000 20 0
* GigabitEthernet1/0/28 0 0 0 0 0 0 12000 11 0
GigabitEthernet1/0/29 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/30 0 0 0 0 1000 1 13000 13 0
GigabitEthernet1/0/31 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/32 0 0 0 0 0 0 12000 13 0
* GigabitEthernet1/0/33 0 0 0 0 0 0 12000 11 0
* GigabitEthernet1/0/34 0 0 0 0 51000 30 434000 56 0
* GigabitEthernet1/0/35 0 0 0 0 0 0 61000 14 0
* GigabitEthernet1/0/36 0 0 0 0 0 0 12000 11 0
* GigabitEthernet1/0/37 0 0 0 0 0 0 172000 42 0
* GigabitEthernet1/0/38 0 0 0 0 0 0 12000 12 0
* GigabitEthernet1/0/39 0 0 0 0 0 0 12000 12 0
* GigabitEthernet1/0/40 0 0 0 0 491000 832 63201000 5869 0
* GigabitEthernet1/0/41 0 0 0 0 1000 1 13000 13 0
* GigabitEthernet1/0/42 0 0 0 0 28000 3 62000 17 0
* GigabitEthernet1/0/43 0 0 0 0 0 0 112000 12 0
GigabitEthernet1/0/44 0 0 0 0 0 0 0 0 0
* GigabitEthernet1/0/45 0 0 0 0 0 0 14000 15 0
GigabitEthernet1/0/46 0 0 0 0 0 0 0 0 0
--More--
I'd start with a show interfaces, for example, the example below. You should be able to see what interfaces (if any) are showing packet errors, at which point you'd need to do some troubleshooting or diagnostics to determine why.
[some-switch-thing]#sh int
FastEthernet0/0 is up, line protocol is up
Hardware is Gt96k FE, address is [some-MAC-address-thing] (bia some-MAC-address-thing)
Internet address is [some-IP-address-thing]
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 112000 bits/sec, 51 packets/sec
5 minute output rate 207000 bits/sec, 46 packets/sec
329320347 packets input, 534153518 bytes
Received 4483582 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog
0 input packets with dribble condition detected
320121443 packets output, 1884667704 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 output buffer failures, 0 output buffers swapped out
answered Mar 12, 2013 at 13:53
