Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

3750 SFP Issues

I am currently using a 3750 switch using an SFP connector.GLC-LH-SM. I have this connecting to a tfoca using a 1m lc to sc connector. It is then transfered over SM fiber for approx 300 meters. The issue is now that we can get transmission for about one minute but the the link-flap error occurs and closes the port. We have disable the port shutting command so it keeps the link alive after 30 seconds. This works like I said for appox 1 minute. Then the port still shuts down. We have tried this for 2 300m reels of tactical fiber but no link lights ever show up. I know that the GLC-LC-SM is capable of MMF but am wondering if this is automatic depending on which fiber you are using. Any help on this would be greatly appriciated.

SSgt Jared M Johnson



Re: 3750 SFP Issues


From your post I am not sure which sort of tfoca you are using. If it is singlemode, you should be O.K. But for connection of GLC-LH-SM module to MMF (and your post perhaps mentions this) you need special so called mode-conditioning patchcord otherwise you will not succeed.

Best regards,


New Member

Re: 3750 SFP Issues


thank you for the reply. We found the solution this morning so life is good. We ended up getting rid of the TFoca box altogether and just using a pigtail straight from the tactical fiber to the LC connection and everything worked perfectly. Thank you for your response, and I'll defenitely ask more questions if any problems come up. Thanks for the help.


New Member

Re: 3750 SFP Issues

This documents describes what would be needed to connect to MM fiber. Cisco suggest you use a mode conditioning cable for this connection. I have seen it work without the cable but it is not recommended by Cisco.

I worked on a tactical network for the last year and we had a setup much like you descibed and it worked fine with the TFOCA cables. I would be glad to discuss specifics if needed. Just email me.