Fibre linking 2 cabs

I need to connect two network cabinets together, call them Cab A and Cab B with B needing to connect to the server via A. The cabs are in different buildings, but on the same site. There is already a fibre link in place but it was decommissioned and now the school want to restore the link.

Both cabs still have the racks in them at either end of the link. I have installed a media converter into Cab A and have connected it up to the fibre rack, and then to the switch. I have installed a switch in Cab B with a fibre module. So if this works, I should be able to plug a computer into the switch in Cab B, get an IP, and be able to ping the server. But I can't.

When I plug the media convertor into Cab A, all the lights are on showing that their is a valid fibre link and the network cable is sending and receiving. In Cab B, the light on the switch for the fibre module is off. However, this fibre module is a "3COM" one and it's a netgear switch, it fits fine and when the module is in place without the cable in it, there is light coming through the port so I don't know if that's an issue.

Only thing I can think of is to purchase another media convertor to put into Cab B? Other than that, I can only say there is a problem with the fibre cable.

Any help would be appreciated.

A quick possibility - have you tried reversing the fibre pair? I have had this problem a couple of times and (with certain connectors) it's possible to have the pair reversed at one end. I have successfully linked 3com and Netgear switches in the way you're describing, so that should be OK.

Have you any other fibres available between the cabinets to try? If you can visually test the fibre with a light source to prove it's OK, then you may well be best off with two matched media converters at each end. When using MCs, I've found they're happiest when a matched pair is used.

A lot of switch vendors are very fussy about brand - HP will only work with HP, Juniper will only work with Juniper etc... so may well be that. Not really a way of telling without buying a new one though, and they're not cheap.

Another possibility, though, is that you just need to explicitly state the connection on the switches at either end - tell them to run at 1000 Full Duplex instead of letting them autonegotiate. I'm all 3COM/HP3COM switches here and even then some of them won't autonegotiate.

I did try reversing the pair and had no joy. One thing I noticed was that when plugging the fibre pair into the rack, the light on the media convertor would come on when the red was plugged into the rack even if the black wasn't. And that the light didn't come on when just the black was in.

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Originally Posted by sonofsanta

Juniper will only work with Juniper

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I know it was an example, but to avoid confusion, Juniper will work with other vendors fibre modules, however if you have a problem Juniper support will require you to be using Juniper modules for them to help you. I use a few of my D-Link modules in my Juniper EX-4500 and SSG-320M without any issues.

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Originally Posted by Kineas

I did try reversing the pair and had no joy. One thing I noticed was that when plugging the fibre pair into the rack, the light on the media convertor would come on when the red was plugged into the rack even if the black wasn't. And that the light didn't come on when just the black was in.

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I've noticed this sort of behaviour before; I have an odd recollection that I managed to 'solve' something like this by rebooting both switches (in a particular order!) after connecting the fibres. But that's a hazy memory of an odd procedure I stumbled across, I'm afraid...!

Media converters are sometimes proprietary, they aren't always using the standard formats for fibre modules. You usually have to have the same media converter on both ends.

We have HP going to CISCO and it works fine, we do however have some weird media converters which only work together and have to be converted back to CAT5 before they can interface with the switches!

The school paid for someone to come in and sort this all out because my experience with fibre is minimal. But basically they left without it being sorted, dumped it all on my lap giving me a list of things to purchase which only included 1 media convertor and told me what to plug in where. This being a waste of time and money as I've done what they've said and it doesn't work.

So am I right in saying that if I was to purchase another media convertor, the exact same as I already have in place in Cab A, that the likelyhood is that it will work? I just don't want to be wasting more money.

Yeah 2 media converters of the same brand.

Check out the page for the media converter and just double check in case the fibre lines are knackered.

Its what we had to do anyway :)

We have used it for linking the CCTV cabs together, otherwise we have used switch to switch GBICs which works interbrand in ours fine.

Ok cool, thanks for your help.

Also check you have the right type of patch leads! We had a company come in and install a fibre link but left the wrong type of patch leads, when questioned the engineer didn't seem to understand why i was asking about the patch leads.

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Originally Posted by dave.81

Also check you have the right type of patch leads! We had a company come in and install a fibre link but left the wrong type of patch leads, when questioned the engineer didn't seem to understand why i was asking about the patch leads.

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Incorrect gauge on the patch leads should still work, it'll just be degraded performance. If it's incorrect connectors then the contractor should be banned from working with fibre, but it seems unlikely to be that wrong!

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Originally Posted by dave.81

Also check you have the right type of patch leads! We had a company come in and install a fibre link but left the wrong type of patch leads, when questioned the engineer didn't seem to understand why i was asking about the patch leads.

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I presume the patch lead is fine as the end with the media convertor is getting activity, it's the other end with just fibre into a module on the switch that isn't getting any activity.

It struck me last night that we have another fibre link in the school to connect to the annex building that we have, so I checked it out. Both ends have a media convertor! I am now 99.9% confident that another media convertor, the exact same as in Cab A, will make this connection work.

Yet more annoyance at this guy that we paid to do this job, didn't even leave me with a full list of items that would be required. To add to this, we host our website through him on his 1&1 web space. The website has been throwing a 404 since last week and can't get hold of him. Very professional.

To me it sounds like the media converter. I've never had a fibre module work with a media converter, or got 2 different models of media converter to connect very well. Often different switch fibre modules dont work together - especially the Cisco ones in my experience.

Also 50/125 fibre might work down a 62.5/125 cable but not the other way round. Like Dave.81 says, check the size of the patch leads match the fibre linking the buildings. Size should be written on the cable coming out of the back of the fibre patch panel.