Trunk issues

[David Hunt]

Hello friends,

I am in the process of swapping out an older 24 port Cisco catalyst 3525 POE switch running IOS 12.0(5) with a 48 port POE catalyst 3560 running ios 12.2(50)

The trunk port on the older switch (that currently works) is in port Gig0/1 with as basic of a trunk config as you might find…

    interface GigabitEthernet0/1

          switchport mode trunk

On the other end of this working trunk is another switch with these settings

          interface GigabitEthernet1/0/8

          switchport trunk encapsulation isl

          switchport mode trunk

Physically, the older switch, has a 1000BaseLX fiber Gbic connected that has a LC-LC fiber cable

From my understanding…

From a trunk to work, the settings need to match on both sides… correct?

So… in the new switch… I have the following configured…

interface GigabitEthernet0/1

switchport trunk encapsulation dot1q

switchport mode trunk

In the newer switch I have a 1000BaseSX SFP min gbic with a SC-LC fiber cable attached (8.3/125 – 15 meter

When I make the connections, I get no lights… no connection… am I missing something? Do I have the wrong hardware at all?

Any help is greatly appreaciated

[Reza Sharifi]

Hi David,

If you don't get link light at all, try to swap the fiber strands around on one side of the link to cross them. It maybe your are connecting tx to tx and not tx to rx. Usually, it is easier to swap the SC side because it is bigger.  Al though you can also swap the LC side, but just do it on one side.

HTH

[acampbell]

David,

A 1000BaseSX SFP is a MULTI-MODE Fibre interface.

A 8.3/125 – 15 meter cable is SINGLE MODE

These 2 are not compabatable.

The correct cable for an SX interface is either 50/125 or 62.5/125

Regards,
Alex.
Please rate useful posts.

[David Hunt]

morning Alex...

that makes perfect sense... So before I just go out an order a new cable... I have to ask... do we have the wrong fiber interface?

I ask becasue... the existing working setup has a single mode fiber cable going into a 1000BaseLX fiber connector.(single mode fiber gbic?).. which makes me wonder if GBICs are mode specific...

If the exisitg setup is single mode... do I need a single mode SFP fiber interface or is just ordering the correct cable good enough?

Thanks

David

[Reza Sharifi]

David,

Your cables need to match with your optics.  If your optics are LX (long haul) your cable need to be single mode.  If your optics are SX then you cable need to be multimode.

HTH

[David Hunt]

Yes, I understand the part about the cables, what I am atempting to clarify is

Will the SFP fiber connector I have.... which 1000BaseSX SFP mini gbic.... which from what you guys are saying is multimode.... work as long as I get the proper cable (multimode)

or

do I need to buy a different SFP fiber connecter that is specific to single mode fiber?

[David Hunt]

To clarify...

since the existing "setup" appears to be a single mode fiber setup... becasue it is working...

do I need to purchase this...

Cisco 1000BASE-LX/LH ShortWavelength Network Adapter

or

will the adapter that I have...

Cisco 1000BaseSX SFP adapter work

if I just get a MM cable?

[Reza Sharifi · Accepted solution]

Correct, If the existing working setup is single mode then you need 1000 base LX/LH.

1000 base SX will not work.  Basically, your optics has to be single mode to match your existing single mode cable.

HTH