Thursday, March 7, 2019

Switchport dark, cabling is good... what is going on?

So we are trying to connect a dumb/unmanaged switch (TrendNet) to our 2960x (for reasons), and the port flashes green briefly then goes dark, and stays dark. The interface says down/down (notconnect).

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No indication in the logs that the interface is even coming up at all. If we take the Trendnet switch out of the equation the network device comes up right away.

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The only configuration is 'switchport mode access' and a description. I've tried trunking, I've tried turning off mdix auto, I've tried turning off PoE, all sorts of stuff.

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I've checked port security, spanning tree, using a crossover cable, not using a crossover cable... no blocked or err-disabled ports, just nothing.

Tested the run end to end, no cabling errors. You can plug a laptop in and get local connectivity. I think the port lights up on a spare Cisco 3750 that we tested that's out of production so we can't just throw it online.

Do you have any idea what is going on? It's frustrating and I feel like I'm missing something really stupid. Is there something with the 2960x's that does not want an unmanaged switch attached?



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