[c-nsp] switch port "shutdown" and "no shutdown"- what exactly happens?

[Ryan Wilkins]

On Jun 2, 2011, at 6:07 AM, Martin T wrote:

> Hi,
> rather stupid subject, but the thing is, that I have one Cisco
> WS-C2950-24 switch, which has one Motorola radio device connected to
> one of fast-ethernet ports:
> 
> WS-C2950-24[Fa0/1] <-> [eth]Motorola_radio_device
> 
> Problem is, that about once every 24h this connection stops forwarding
> traffic. I have changed the fast-ethernet ports in WS-C2950-24 switch
> and even replaced the switch with a new one, I have replaced the
> Motorola_radio_device, there are no interface flaps and errors on
> switch port, nothing interesting in the Motorola_radio_device log
> file. Both devices are behind the proper UPS. Once the traffic between
> those two devices stops, simple "shutdown" and "no shutdown" to the
> switch port helps. Cat5e cable between the devices is 75m(246 feet)
> long. One might suspect the cable/connectors, but on the other hand
> there really are no errors on the switch port. What might cause the
> issue where reinitialization of the Ethernet port reallows traffic
> forwarding? Might there be a possibility to reproduce such situation
> in the lab?

Have you noticed if the port goes into a "err-disable" state?
Also, have you checked spanning-tree to see if it's blocking the port for some reason?
What radio are you running?  I've got a couple pairs of Motorola PTP 800 radios and a couple pairs of BridgeWave FlexPort 80 radios on my switches (3560G) with no real issues.  Some of the radios have a feature built in where they'll momentarily drop the Ethernet link if there is a perceived problem with the radio link, although you'd think it'd log if it did this.  I'm just wondering if the port detects a loop and shuts down.
As others have suggested, you may have RF leaking back into your switch.  RFI can cause all sorts of strange problems.  Are there other transmitters near by yours that may possibly be causing problems?

Regards,
Ryan Wilkins