When you have a native VLAN mismatch on a configured trunk, which protocol will alert you to the issue?

A. VTP
B. CDP
C. 802.1Q
D. ISL

B. Cisco Discovery Protocol (CDP) will alert you to a native VLAN mismatch. You will receive the error:

%CDP-4- NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered…

when a trunk is configured, the native VLAN is always used for CDP exchanges.