Error disabled problem in a switch

[tiwariharish44]

Hi,

We have a cisco 2960 switch that has its some ports getting error disabled time and again. When we issue show int fa0/X command, CRC and Input errors are seen.

The user has changed their LAN cable, we have replaced the LAN port at user end. But still the problem is there.

Now there is only one possibility that may be the cable running from switch to user LAN port is faulty. But can so many cables be faulty on the same switch??? Or can it be related to some IOS issue?

[tiwariharish44]

Hi, the output is attached here. And we are using port security as you can see from the show run interface output.

Why is it showing link flap error?

[Leo Laohoo]

Error-disable caused by "link flap".  This means there's a potential Layer 1 issue.  

The ports are also FastEthernet ports.  Can you post the complete output to the command "sh interface <PORTS>"?

[Andre Neethling]

Link Flap could definitely be a layer 1 issue. "sh interface" would shed more light on the potential cause.

[tiwariharish44]

Please go through the attached file.
 

[Andre Neethling]

You have CRC and input errors on all those interfaces. What are the approximate cable lengths? It seems as if you could have cable issues. Why do you have the speed set to 10mbps?

[tiwariharish44]

sh interface<interface no.> I have already posted in one of my comments

[tiwariharish44]

Hi

Please see the show int output as attached.

[Leo Laohoo]

Ok, just as suspected.  Look at the output you've provided.  Each of the affected interfaces has very high CRC errors.  It's a Layer 1 issue.  

Can you describe what is the exact model of your switch?  I also would like to know what is the IOS your switch is running. 

... Wait a second.  WTF is the configuration of the ports involved?  All the ports are running 10 Mbps, Full-Duplex.  The port speed and duplex setting is hard-coded.  Can you please post the output to the command "sh controll e <PORTS>" as well as the configuration of your ports involved?

[tiwariharish44]

The output you asked  is attached here.

But can this error disable problem has something to do with the ports configuration??? seems unlikely...

[Leo Laohoo]

Thanks for the output.  Very helpful. 

I've seen line errors before and I've seen large quantity of line errors.  Your output has the hallmark of a possible cable issue due to the presence of significant amount of FCS and concurrent Alignment errors.  

Next, I want to know why you've hard-coded the speed and duplex settings.  Is the intention meant to SLOW DOWN this connection?

[tiwariharish44]

yes the 10 mbps speed is enough for the students in their hostels, for all the hostel area we have done the same.

[Leo Laohoo]

yes the 10 mbps speed is enough for the students in their hostels, for all the hostel area we have done the same.

I disagree.  Hard-code the speed and duplex setting and your students will get LESS THAN 10 Mbps.  It's more like 5 Mbps.  Frankly, if you want to PUNISH your students for using your network then setting the speed/duplex settings on the switch port is downright stupid if not dumb.  I would not be punishing students for using the network.  If you want to throttle their use of the internet, however, is totally different to what you're using now.  

I really don't understand the logic and concept behind slowing down the port speed in student living areas.  I mean, WHY BOTHER giving them network access in the first place?

[tiwariharish44]

I don't know why you have any problem with our port's configurations. I simply asked in the forum about ports getting error disabled, and everyone here seems to be offended by it. I mean, come on guys, its our network, whatever the management decides, it's upto them

[Leo Laohoo]

I don't know why you have any problem with our port's configurations. I simply asked in the forum about ports getting error disabled, and everyone here seems to be offended by it. 

We're not offended by it.  We're saying it's "stupid".  How it's done and why is done.  It's just plain dumb.  If you want to slow down their INTERNET access, then there's a better way of doing things by using policy shaping.  Slowing their port connection down to 10Mbps/Half duplex is not a smart way of doing things because you disable a feature that may determine why the ports are getting error-disable.  

I manage schools (>95 sites).  We don't punish our student body this way.  It's too archaic and very "old school".  Would work if you have an old network, like Token Ring.  With Ethernet, you need a little bit of smarts to it.  

[tiwariharish44]

Ok Leo,

I will put the ports to auto speed and duplex, now tell me which feature will now be enabled so that I can know the reason behind the ports getting error-disabled.