Dell PowerConnect 3524 Cli Reference Manual page 390

User Guidelines
Root guard can be enabled when the switch works in STP , RSTP and MSTP .
When root guard is enabled, if spanning-tree calculations cause a port to be selected as the root port, the
port transitions to the alternate state.
Example
The following example enable root guard on port e8.
Console(config)# interface ethernet 1/e8
Console(config-if)# spanning-tree guard root
390
Spanning-Tree Commands