Root Guard

Root Guard
Root Guard is meant to prevent the wrong switch from becoming the spanningtree
root. It is enabled on ports other than the root port and on switches other
than the root. If a Root Guard port receives a BPDU that causes it to become
a root port, the port is put into a “root-inconsistent” state and does not pass
traffic through it. If the port stops receiving these BPDUs, it automatically
re-enables itself.
Switch(config-if)#spanning-tree guard root
Switch#show spanning-tree inconsistentports