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New Member

S.T. to S.C fiber connectivity issue


I have cisco 4503 switch ... I want to terminate fiber connection from one of the local branch to this switch. cisco 4503 are having total 8 port with 1 gb

i have S.T. connection which has come to local office and i would like to connect to 4503 switch with S.T. to S.C cable but link is not coming up.

what could be issue?

I am new in fiber ..

I have couple of doubts with fiber connectivity..

If i have S.C. to S.C. or LC to LC or any type i want to connect two devices, how do we check with link status LED ? whether link is working

I mean , do we have different configuration or connectivity procedure for fiber campared to UTP connection.

Please share the details

It would be appreciative to get the answer for my basic doubts about fiber connectivity..

Cisco Employee

Re: S.T. to S.C fiber connectivity issue

Hi Vinod,

There is no any specific configuration needed compare to UTP. ST to SC fiber just has different connector types but there are no any conversion inside and hence a connector type is not important here.

  • Do you know what is the span loss on this fiber? That is to be sure we are in optical power budget for the 4503 connectors.
  • Do you have an optical power meter? You can verify if we get any power coming from the remote end.
  • Is there DWDM/SONET/SDH on that fiber? You may want to disable an autonegotioation on the link as Fast Link Pulses won’t go through majority of equipment.
  • To verify the cat4k itself, put a physical loop on a port connecting Rx and Tx by one cable. The link must be up and you should see yourself as a CDP neighbor.



New Member

Re: S.T. to S.C fiber connectivity issue


I would like to take the opportunity to express my tons of thanks to you for sharing imp. information with me.

I have some couple of doubt as you have raised some question

If i give , no shut command in interface mode .... why the status LED goes off which is amber before ?

I do not have fiber power meter ..

Anyway, I will check connecting back to back to my cat4k and will confirm that module is fine...

Re: S.T. to S.C fiber connectivity issue

A couple of questions:

1)  Is the optical transceiver module (GBIC) installed in your 4503 the same type as in the equipment at the other end of the fiber?

2)  Do you know what type of fiber, singlemode (SMF) or multimode (MMF) is connected to the ST connector coming into your local office?  What type of ST-SC jumper cable are you using?

3) Make sure you have the fibers connected to the correct port (Far end transmit port connects to near end receive port and vice-versa).

The following Cisco Troubleshooting Guide might help...


Let us know if you have additional questions.



New Member

Re: S.T. to S.C fiber connectivity issue

I only glanced at this, but something else to consider... Are you using short haul or long haul GBICs?  If the

end-node GBICs aren't the same, the link will not come up.