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UDLD and Fibre/Copper Media Converters

We have a remote site connecting with two 100Mbps LAN-extension services, where the Telco provides a fibre/copper media converter at each end of the dark fibre link. One of these links developed a fault where one of the pairs of fibres became disconnected and resulted in a unidirectional link. Consequently, this caused a spanning tree issue and affected network stability. Would UDLD work in this scenario where the switch ports are on copper (which connect to the media converter), as opposed to direct fibre ports on the switch?

Is it likely that this instability (caused by a STP loop) could have caused HSRP instability in other VLANs?


Re: UDLD and Fibre/Copper Media Converters

I think if you enable UDLD on the switches attached to the media converters, it will be disabled on the copper ports by default. It's only enabled by default on fiber interfaces. It is something you can turn on or off per-port, though. This should detect that there's something wrong with the link if you run into another down strand resulting in a UDL: failure of the acknowledgement echoes to come back into that port should shut the port down, whether the interface is directly connected to the media or converted.

Some media converters have the ability to shut down their copper interface if the fiber is not working properly. Only when both copper and fiber are plugged in properly does the converter pass link and data traffic through. (Transition Networks is one company whose products do this; we use these exclusively.) UDLD would not be necessary with these.

Would need to know more about your network design in order to comment specifically on whether the STP problem caused the HSRP instability; but it is a possibility.

Hope this helps.

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