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3550 Switch - Input errors

Hi all!

I had an experience on one of my many 3550 switches.

A customer called and said that he couldn't connect to the internet one evening. When first line support went to have a look, he observed that both of the status LED's on the NIC flashed in a sequense like. This indicates it's a cabling fault I guessed. But when I went there myself everything on the NIC was ok, but I couldn't connect to the network. I did I receive an IP-address from the DHCP-server, and setting a static IP didn't work out neither.

I logged on to the switch and issued an "sh int fa0/12" command, and discovered around 700 input errors (700 CRC). I tried to shutdown/no shutdown on the interface, but this had no impact, I still couldn't get connected. The interface was not in error-disabled state when I checked.

This type of error I've now experienced 3 times on my 3550 switches.

So why is the interface not working? Is it broken?
I thinks it is a software issue, but have no idea what to do to fix it / reset the interface and prevent this error to happen again.

Thanks in advance for bringing some qualified answers.

Everyone's tags (3)
Cisco Employee

Re: 3550 Switch - Input errors


Can you provide me with the output of "show ver" from the 3550 along with the output of "show controller ethernet fa0/12"? What connects to this port?




Re: 3550 Switch - Input errors

It is on the correct VLAN. It's a normal PC connected to this int.

No messages in the log relating to the particular int.

Do you think a reload would solve the problem?

Here you go!

Show version:

Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(35)SE3, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Fri 16-Mar-07 00:43 by antonino
Image text-base: 0x00003000, data-base: 0x00E86000

ROM: Bootstrap program is C3550 boot loader

143-DK03-24-01 uptime is 33 weeks, 6 days, 3 hours, 2 minutes
System returned to ROM by power-on
System restarted at 13:51:11 CET Tue Apr 13 2010
System image file is "flash:c3550-ipservicesk9-mz.122-35.SE3.bin"

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:

If you require further assistance please contact us by sending email to

Cisco WS-C3550-24 (PowerPC) processor (revision K0) with 65526K/8192K bytes of memory.
Processor board ID CAT0752R1FK
Last reset from warm-reset
Running Layer2/3 Switching Image

Ethernet-controller 1 has 12 Fast Ethernet/IEEE 802.3 interfaces

Ethernet-controller 2 has 12 Fast Ethernet/IEEE 802.3 interfaces

Ethernet-controller 3 has 1 Gigabit Ethernet/IEEE 802.3 interface

Ethernet-controller 4 has 1 Gigabit Ethernet/IEEE 802.3 interface

24 FastEthernet interfaces
2 Gigabit Ethernet interfaces

The password-recovery mechanism is enabled.
384K bytes of flash-simulated NVRAM.
Base ethernet MAC Address: 00:0E:D7:66:5E:80
Motherboard assembly number: 73-5700-10
Power supply part number: 34-0966-03
Motherboard serial number: CAT0752034L
Power supply serial number: DTH07502DA4
Model revision number: K0
Motherboard revision number: A0
Model number: WS-C3550-24-SMI
System serial number: CAT0752R1FK
Configuration register is 0x10F

sh controllers ethernet-controller fa0/12 (I shut down the interface, because I used a different int for this client)

  Transmit FastEthernet0/12          Receive
851425559 Bytes               2105008660 Bytes
  21685532 Unicast frames        13010159 Unicast frames
    369183 Multicast frames        545763 Multicast frames
    183747 Broadcast frames        531111 Broadcast frames
         0 Discarded frames           382 No dest, unicast
         0 Too old frames             361 No dest, multicast
         0 Deferred frames             18 No dest, broadcast
         0  1 collision frames
         0  2 collision frames        719 FCS errors
         0  3 collision frames          0 Oversize frames
         0  4 collision frames          0 Undersize frames
         0  5 collision frames         88 Collision fragments
         0  6 collision frames
         0  7 collision frames    7887618 Minimum size frames
         0  8 collision frames    3101005 65 to 127 byte frames
         0  9 collision frames    1894110 128 to 255 byte frames
         0 10 collision frames     348463 256 to 511 byte frames
         0 11 collision frames     687490 512 to 1023 byte frames
         0 12 collision frames     245308 1024 to 1518 byte frames
         0 13 collision frames
         0 14 collision frames          0 Flooded frames
         0 15 collision frames          0 Overrun frames
         0 Excessive collisions         0 VLAN filtered frames
         0 Late collisions              0 Source routed frames
         0 Good (1 coll) frames         0 Valid oversize frames
         0 Good(>1 coll) frames         0 Pause frames
         0 Pause frames             98760 Symbol error frames
         0 VLAN discard frames          0 Invalid frames, too large
         0 Excess defer frames          0 Valid frames, too large
         0 Too large frames         23367 Invalid frames, too small
   2383852 64 byte frames               0 Valid frames, too small
   1336771 127 byte frames
   1795869 255 byte frames
    752333 511 byte frames
    376429 1023 byte frames
  15593208 1518 byte frames

Cisco Employee

Re: 3550 Switch - Input errors


1. Can you check if you learn the MAC address of PC and router on your switch?. Check "show mac-address-table vlan <>"

2. Check if those counters (CRC errors or packet counters) increasing on ports connected to PC as well on router.

3. As suggetsed by others, check if you have PC and rotuer on same VLAN.

Try configuring interface vlan on 3550, assign IP address from same subnet as PC/Router and try pinging both.




Re: 3550 Switch - Input errors

700 input errors isnt really very much. And depending on when the switch was restarted latest or had its counters reset they might have been there for a long time.

Did you have any messages in the log relating to the port?

You probably checked this, but whas the interface configured for the right VLAN?


Re: 3550 Switch - Input errors

I see :

         0  2 collision frames        719 FCS errors
         0  5 collision frames         88 Collision fragments

Can you hard set the speed duplex settings on both sides if not done already.



Re: 3550 Switch - Input errors


I've now testet a bit, of what you requested.

By the way. This problem suddenly arose  without any config change.


The switch didn't learn the MAC-address of the PC when connected to the interface.

There was no errors on the router.

I didn't try to configure the L3 interface on the switch, becuase every other port on the switch works fine.

I didn't get any in/output errors when I tried to connect my laptop on the interface today. Could be the counters hasn't been reset for a while.

When connected to the faulty interface, I did get the CDP-message from the switch (using Wireshark).

Finaly I tried to reload the switch - and after that, the port worked perfectly!

Could it be the mac-address-table that needed to be cleared? (clear mac-address-table)

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