Can I reset a port on a Catalyst switch?

whiteford · ‎01-08-2008

Hi, I have a Cisco 2950 and 3560 Catalyst switch and I was wonderign what useful commands I can use to see if the switch or a particular port/vlan has problems like collisions or bottlenecks. If things are slow I normally reboot the switch and things are ok again, but I think I need to look at the problem closer and at a port level, so I wondered what you experts do?

Thanks in advance.

Jon Marshall · ‎01-08-2008

Hi Andy

First, most obvious thing to do is a

"sh int fa0/1" which gives you all the statistics for that partcular interface. It will show collisions/runts/giants etc. plus packet drops.

As for rebooting the switch that is an absolute last resort and to be honest very rarely has rebooting a Cisco switch fixed the problem. It may temporarily relieve it but it will still come back. Unlike Windows where rebooting does actually seem to fix problems in the Cisco world, unless the switch/router has actually frozen it really doesn't achieve that much.

You can always do a shut / no shut on the interface ie.

int fa0/1

shut

int fa0/1

no shut

HTH

Jon

whiteford · ‎01-08-2008

I see 2 input errors, what does this mean?

switch#sh interfaces fastEthernet 0/23

FastEthernet0/23 is up, line protocol is up (connected)

Hardware is Fast Ethernet, address is 000f.2477.0417 (bia 000f.2477.0417)

Description: CBS US VPN

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, media type is 100BaseTX

input flow-control is unsupported output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input never, output 00:00:01, 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 1000 bits/sec, 1 packets/sec

5 minute output rate 1000 bits/sec, 1 packets/sec

22923 packets input, 4615027 bytes, 0 no buffer

Received 12 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

2 input errors, 2 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

38924 packets output, 6650120 bytes, 0 underruns

0 output errors, 0 collisions, 2 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

PAUL TRIVINO · ‎01-08-2008

Check those error counts again, but for those few packets I would *guess* the CRC errors were when you first plugged in the cable. I see that from time to time. If the counters don't go up don't sweat 2 CRC errors. If you clear the counters "clear counters Fa0/23" and the errors stay zero, you're good.

Rick Morris · ‎01-08-2008

you may want to also check the CPU utilization and see what percentage of the CPU you are using. High CPU rates cause slowness too.

whiteford · ‎01-08-2008

My SNMP server monitors the CPU and mem and it's very low.