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Beginner

Issue with trunk port over media converter

Hello,

I have two Cisco devices setup to talk to each other on trunk ports. The devices are a Cisco 3560 and a Cosco 2950. I setup fastethernet 0/1 port on both to be the trunk port between the two. First I set them up both to be dynamic desireable, and I tested by running a straight through network cable between the two. It worked just fine and my vlans and everything was functioning as it should.

When I tried to move them to production I ran into an issue. the link between the two is via media converters/fiber. When I went to hook the two up, it did nothing. No ports would light up on either side. I tried making them both "trunk" ports (no dynamic) with dot1q encapsulation on the 3560. Still would not work. I also made sure both were no shutdown.

When I pulled the connection (media converter) from the 3560 and placed it back into the old 2950 it was originally in (old 2950-no trunk port to new 2950-trunk port on fe0/1) now the ports lit up and turned green. I do need the trunk coming from the 3560 working though.

I think I've narrowed down the issue to the 3560, but I'm not sure what it wrong. Can you help me get this working?

Thanks

6 REPLIES 6
Beginner

Issue with trunk port over media converter

Have you tried interchanging the wires in the  fiber converter.I think its a physical connectivity problem.

In the new cisco switches default encapsulation will be dot.1q,cisco no longer supports ISL trunking.

Beginner

Issue with trunk port over media converter

All of the wiring works good because the setup now (legacy setup that I need to change) works fine. Currently one end of the media converter link is hooked into a 2950 and the other end is going to a smaller Cisco switch. The end devices on that smaller Cisco switch communicate back fine, which rules out physical issues with the media converter or wiring.

And both ports on my test equipment work fine because I hooked up a straight through between ports and got a link (with good data).

Thank for the info on the trunking encapsulation info. That is definitely good to keep in mind.

Advisor

Re: Issue with trunk port over media converter

   You have cabling issues or issues with the 3560 or 2950 port speed and duplex setup.  Normally it takes a crossover cable not straight thru  between switches unless auto mdix is supported .  Auto mdix is supported on the 3560 but only if the port speed and duplex is set to auto  on the 3560. The 3560 will then auto correct for the incorrect cable.If you hardcode the port speed and duplex and you have the wrong cable it will just shutdown the port.   The 2950 does not support auto mdix so you have to have the correct cable when you plug into the media converter, so it may work betwetween the 2950 and the 3560 because the 3560 auto corrects for the wrong wiring but it may not work with the media converter. If you got no link on the 3560 side to the media converter verify port speed setting is at auto for speed and duplex , if you hard coded the port that may not work either.  Check media convertor specs on what the copper interface supports. The smaller cisco switch works ok because probably that supports the mdix function also.

Beginner

Issue with trunk port over media converter

1)Both the switches are working with RJ 47 cables.When its connected through fiber ,its not connecting.

2)Try to interchange the fiber cables as shown for part 2 and 3.when you have inserted the module,type the command "sh log" or "sh logging".

If any errors in supporting of the module or any other issues it will get highlighted

3)which is the current fiber module you are using (multimode or single mode).Are you using same type of fiber module on both end of new switches.

Beginner

Issue with trunk port over media converter

Hey guys,

Thanks for chiming in. Guru, I should have been more specific with the media converter definition in my case. sorry. The media converter that I am using is one that converts multimode fiber with ST connectors to copper RJ-45. I thought about using the Gb ports like in your picture but the fiber coming in has the ST and not the LC connectors needed.

Glen, that does make sense what you wrote. One question though, I did try to change out one of the copper cables over to a crossover cable coming off of the media converter. It still did not detect. Do I need to change both copper cables (on each end) over to crossover cables to have it correctly crossed over?

In the meantime I am going to look into the media converter specs if I can and also check the port settings. Thanks

Advisor

Re: Issue with trunk port over media converter

   the copper connection is local so when you get the cable correct the link light on the switch and convertor should go green .  I believe I have seen where one end or the other does not have a link the other end will not come up, that's a convertor setting usually that controls that . The 3560 end should be set to auto for speed and duplex  and enter the mdix auto on the port just to make sure it is turned on .

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