Netgear GS748TPS Switch not communicating with network over fibre

For the last couple of months we have had a Netgear GS748TPS happily communicating with our core switch via a fibre link.

After a powerdown of all our equipment it stopped working properly.

The port with the Fibre module lights up green and and flashes away to show that it is communicting with the core switch (Netgear GSM7328FS), but it is not pingable and any client plugged into the GS758TPS switch cannot contact anything else on the network.

If I remove the fibre connection and try a Cat5e connection, the switch becomes pingable and the clients attached can communicate with the rest of the network.  This only happens when connecting with the Fibre.

Things we have tried:

* Factory reset the switch and set it up from scratch
* Update Firmware
* Change the switch for another brand new identical switch (we have a few at the moment as we are refreshing a lot of our equipment)
* Plugging the switch directly (with a 2m fibre patch cable) into the core switch

Whatever I try, the same thing seems to happen.....the lights flash either end to show communication, but the switch or any of the clients connected cannot communicate with the rest of the network.

If I change the fibre uplink or cat5, it works fine.

As we have changed the switch, it makes me thing that it is a setting on the GSM7328FS core switch, but I dont know what this might be as it has been working fine for the last couple of months.

Any help appreciated!
stalbansschoolAsked:
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TimotiStDatacenter TechnicianCommented:
I'd guess one of the SFP transceivers burned out. I had cases where the link LED came online, only it wasn't passing traffic, or only at ~4Mbps with lots of errors.

Tamas
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stalbansschoolAuthor Commented:
Sorry, forgot to say that we also have a load of SFP tranceivers and we have tried replacing those as well
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stalbansschoolAuthor Commented:
Some more experimenting seems to also suggest that connecting via CAT5 does NOT work on the core switch as I incorreclty said in my first post.

However, if I connect via CAT5 to a different switch further down the chain, this does work.
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stalbansschoolAuthor Commented:
As a side peice of information which is probably not relevant, I cannot seem to save the 'local' time on the switch.

If I try to configure the time and apply it, it resets back to its default date (sometime in 2008) after the switch reboots.

Not sure if this is relevant...
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TimotiStDatacenter TechnicianCommented:
Idea: maybe it's a spanning tree issue? Check the STP status on the relevant ports, with and without another switch in-between.
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Khandakar Ashfaqur RahmanExpert/ConsultantCommented:
Switch off the fiber module.

Then install Packet Analyzer into a pc like wireshark.Mirror your switchport and start PKT monitoring.
http://www.wireshark.org/download.html

Now you turn on Fiber module.Analyze wireshark pkt.
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stalbansschoolAuthor Commented:
Yes! Thank you!

By disablling STP on the switch, it is now working correctly.

Great suggestion, thanks!
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TimotiStDatacenter TechnicianCommented:
While this may be a good temporary solution, if you had STP issues, there might be a loop or something in your network.
You should check everywhere for rogue switches/connections/whatever, and fix your network so it works again with STP. It's a good protocol to safeguard against problems.

Tamas
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