Giga Connexion KO

Unanswered Question
Aug 20th, 2010


As I mentioned in another thread, I am currently doing an apprenticeship program in a business with lots of Cisco switches and routers.

One of the employee, tried to connect 2 switches between each other using the Gigabit interfaces and using the module GLC-SX-MM for fiber. The result was no connection and the interfaces KO. As I am here to learn more about cisco... I set up 2 switches in lab to reproduce exactly the same situation.

1. 1x Switch 3750 and 1x Switch 2960.

2. I did the trunking using and ethernet cable and everything worked fine and could make the pings....

3. I then set up the modules GLC-SX-MM and inserted the fiber. At the point everything was KO. I tried again with the ethernet cable and it was OK.

4. The interfaces are up, the config is correct.... I tried with other modules and still KO.

5 What is interesting is that they have other 3750 and 2960 on their network and everything is OK.

Any ideas ?

thanks a lot.


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
rtjensen4 Fri, 08/20/2010 - 05:20

Did you cross your TX and RX fibers on the other switch? I've been burned by that before. Also, if the SFP ports are dual purpose (either RJ-45 or SFP), try to define the media type under the interface config. I believe the command is media-type rj45|sfp

emanjamin2002 Fri, 08/20/2010 - 06:41

Thanks a lot for your answer.

For the 2960 : the media type worked or I could say that I manage to run that command.

For the 3750 : this command doesn't exist. I did go into the config mode for the Interface Gigabit 1/0/1 but I can't run the media type ?

Thanks again.


rtjensen4 Fri, 08/20/2010 - 06:55

Yeah, that command only works if the ports are dual-purpose.

Did you verify that the TX fiber from one switch was going to RX on the other and vice versa?

emanjamin2002 Fri, 08/20/2010 - 07:15


Yes I checked the fiber to make sure it was fine on both end. I even tried it the other way aroun lol to see if I was doing it wrong. Well this is the WE here in France, so I am going out to take a walk and get my mind working for me.

thanks again and hopefully I will find the answer soon !!! and thanks for your advices again.


emanjamin2002 Fri, 08/20/2010 - 06:58

Me, again !! well I checked the interface and it is in SFP for the 3750 but still KO between both switches. I tried with the ethernet cable and it is OK. ??

I have to study more things it looks like. If anyone has more idea, it would be appreciated.

Thanks again.


emanjamin2002 Tue, 08/24/2010 - 01:51

Hello again,

So I manage to make it work with the module fiber. It was a problem with the configuration.

But now I have another question.

I want to order some GLC-SX-MM to use on the switches which will be enough for the distance... I have some spares here that I am using in lab for testing but they don't work ???? when I use the GLC-LH-SM, everything is fine. I thought that maybe the GLC-SX-MM was KO but I have 10 of them and I don't think that all of them are KO.

Is there a difference between them or something I should do on the switches ??? (except the differences in distance...). Weird as this is working with the LH-SM, so it should also work with the SX-MM ???




This Discussion