Upgraded my old switch setup and lost a whole floor of connectivity

I swapped out a 10 year old 48 port switch at our office in Austin last month, figured it would be a simple lift and shift. Plugged everything in, watched the lights blink, and then half the conference room phones went dead. Turns out the new unit had a different default VLAN config and the old one had been running on a messed up trunk port for years. I learned to check the running config before touching anything, not just assume the new gear will match. Has anyone else had a switch upgrade expose messy legacy settings they had no idea about?

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shane_ross23d ago

Blame the vendor documentation on that one too. The new switch ships with VLAN 1 as the native on every port, and the old gear had been quietly forwarding untagged traffic on a trunk that someone set up back when Obama was president. I found six dead ports like that once because the old config had a vlan mapping that was never written down anywhere. Now I take a screenshot of the current switch state before I even pull the first cable, and I label every port with a Sharpie just in case. It's always the stuff nobody touched for years that bites you, not the stuff you actually changed.

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