LC-SC between 2960G and 3548LX

Unanswered Question
May 7th, 2008

Hi all,

For the life of me, I cannot get a fiber connection to work between a Catalyst 2960G with SFP ports, and the 3548XL gigabit ports...what am I missing?

I thought the fiber might be the problem, as I was originally using Single-mode. But I tried Multi-mode as well and still no luck.

Both ports are "no shut", and a Show Int on both shows that they recognize the gigabit modules.

The 2960G is going to be the "core" switch that the 3548XL's use.

Let me know if you need more information from me.



I have this problem too.
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mwall1 Sat, 05/10/2008 - 08:45


Thanks for the suggestion. dice.

Both switches recognize the correct modules installed, but both say "disconnect". Really strange behavior.

andrew.butterworth Sat, 05/10/2008 - 09:15

You are using the same type of 1000BaseX modules aren't you? i.e. 1000BaseSX or 1000BaseLX/LH, you can't interconnect a 1000BaseSX to a 1000BaseLX/LH. If you type 'show interface GigabitEthernetX/X' on both devices it should tell you the type of SFP or GBIC installed.


dbroder Sat, 05/10/2008 - 09:20

Bad cable/GBIC/SFP perhaps? Use spares one at a time to test layer 1.


Sushil Kumar Katre Sun, 05/11/2008 - 09:38

Hi Mike,

Can you let us know what fiber standard are you using on both the switches [1000base-SX, ZX, LX/LX] and the cable information whether its Multinode or single mode.

Also include th part number of the SFP and GBIC.

-> Sushil

mwall1 Mon, 05/19/2008 - 12:57

Hi all,

Thanks for the responses so far.

I was thinking this was a problem between the modules, but both turned out to be SX. (The SFP in the 2960G is a generic module...not much identifying information on it other than "1000BASE-SX SFP)

The GBIC is Cisco (pretty sure legit), model WS-G5484 1000BASE-SX.

I've tried both single and multi-mode fiber with no luck.

Thanks again,


dbroder Mon, 05/19/2008 - 18:36

Do you have a Cisco SFP? If you end up taking this up with Cisco TAC, the first thing they'll do is have you use legit Cisco modules on both sides.

Have you swapped out the fiber cables?


Sushil Kumar Katre Mon, 05/19/2008 - 19:53

Hi Mike,

As far as I know Third Party/Generic GBICs/SFPs are not supported by Cisco Switches. This might be the reason why the connectivity is not coming up. - states-

"Note Because of interoperability issues, Cisco does not support GBICs purchased from third-party vendors."

Look for the following errors on the switch where you are using generic switch -

%SYS-4-PORT_GBICBADEEPROM: port bad gbic eeprom checksum

%SYS-4-PORT_GBICNOTSUPP: port gbic not supported

Suggestion : Purchase a Cisco SFP for 2960G switch.

-> Sushil

mwall1 Tue, 05/20/2008 - 07:50

True, the 3rd-party modules are NOT supported by Cisco, but that is in regards to a TAC request. The hardware itself is generally recognized by the switch, and gives no errors. I've used plenty of 3rd-party GBICs that have worked since Day 1.

In this case, the 2960G isn't reporting any errors on the port, and on a Show int command says "media type is 1000BaseSX SFP", rather than "media type is Not Present".

However, I just read here that the minimum cable length for an SFP module is 6.5 feet.

The cable I had been testing with is only 6 feet (Tripp-Lite N316-02M), so I'm off to find a longer one. Will report back on whether or not it made a difference.


mwall1 Wed, 05/21/2008 - 12:06


It turned out that what I read WAS the problem...the cable was not long enough. I used a 10 foot fiber cable instead, and it now works.

The other cable was only off by 6 inches, but I guess that made a big enough difference!

Thanks to all that responded.


kelly.rosal Sun, 08/31/2008 - 11:08

LC-SC Cable for 2960G.

Hello, So are you saying that the total length of the fiber connector needs to be 6', or you need a total of 6' before the adapter cable. (mine are only a 1' in length)

I'm also not getting any light on my switches SFP port, and when I do a show only my 24 ports ethernet ports are listed.

Thank you,


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