Switch automatically switching from General to Trunk mode

[ronni3]

We have a few CBS 250 series switches. Unsure why, but every once in a while (usually seems like after a reboot), but certain interfaces on the switch that are set to general mode will automatically switch itself over to trunk mode. Any ideas why this may happen?

[balaji.bandi]

maybe a bug, what version of the firmware it running?

[Richard Burts]

What device(s) are connected on these ports? Is it possible that the connected device has initiated negotiation for trunking and your switch negotiated the trunking more?

[ronni3]

3.0.0.61

[balaji.bandi]

thank you for the version information, can you also post-show run from the command level and tell us what port is that you referring to.

one of the post mentions, since these are smart ports, may be wroth remove no smart port config and test it.

[Karsten Iwen]

This is most likely the typical "works as designed but not as expected"-behaviour of the small-business switches. They have Auto-Smartports enabled by default and when a device reboots the link gets reevaluated and the matching macro is applied.

I always disable this functionality as one of the first actions when setting up one of these devices.

https://www.cisco.com/c/en/us/support/docs/smb/switches/Cisco-Business-Switching/kmgmt-2797-smartport-best-practices-CBS.html