%CDP-4-DUPLEX_MISMATCH

This does mean, there is an Duplex Mismatch. Try to configure the port with a static duplex setting. Turn of autosensing. In my experience autosensing very often leads to problems with links. I had this on Gigabyte Ports. The port could not resolve this on his own, i had to setup a static setting to keep the port in a stable state.

You can turn of this messages also with:

no cdp log mismatch duplex

on a router or

turn of cdp on a switch with

no cdp run

either on the interface or globaly.

This could be necessary if you have a dumb device in between. For example connecting a no name switch with a cisco switch. Then the CDP does not discover the speed of the connecting device in the right way and complains about. You should check interface stats, to see if there are any errors on the link. If not, this is an cdp „error“

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