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As said, changing the MTU on a SFP interface of a WS-12-250-DC crashes the switch. I had to manually cut the power to it to regain access. The switch boots with the old config.

Tried on 1.5.5 and 1.5.14, and with 2000 and 9600 MTU. Changing MTU on the electric ports works OK.

Please tell me if I can provide more info. I have attached the edited config at https://pastebin.com/iYYvMZTR

Screenshot at https://imgur.com/a/BySxGRi

Thanks

I think the problem you're seeing is the SFP port goes down and doesn't come back up.

I've experienced this myself with adding vlans.

A few of us have reported this as a bug already.

You said you had to manually cut the power... It's interesting the switch didn't revert the config on it's own. Did you wait longer than the Revert Timer and see if the switch came back online with the old config on it's own?

Did we ever resolve this? I too am seeing this behavior on SFP ports. The switch will eventually revert the configuration, but the port remains in an inop state until you manually unplug and replug in the media.

OK this is more than likely due to an incompatible SFP module.

The reason it reverts to old config is because it lost connection to you because the SFP port did not come back up and the switch could not talk to you so it reverts to old configuration as the switch thinks since it can no longer talk to you the config was a mistake.

See these OLD post discussing SFP modules:

viewtopic.php?f=6&t=293&p=36438&hilit=compatible+sfp#p36438

viewtopic.php?f=17&t=7375&p=36471&hilit=compatible+sfp#p36471