The setting: two Catalyst switches. On each one of them I created two VLANs. A trunk between both switches is set up.
I shutdown the trunk port on side A:
No more VLANs are detected on the local trunk port:
However, side B’s trunk port is still untouched. And it shows a list of allowed VLANs on the trunk, as if nothing special has happened:
Even if the trunking seems to be OK on one switch, we should check the trunk on both sides of the switches.