Allied Telesis AT-FS970M Series - Manual (Page 852)

Chapter 56: Multiple Spanning Tree Protocol
852
MSTP Root Guard
The Root Guard feature enforces the root bridge placement in a network.
It ensures the port that you have configured with the Root Guard feature is
a designated port. Normally, root bridge ports are all designated ports,
unless two or more ports of the root bridge are connected.
If the bridge receives a superior BPDU on a root-designated port, the Root
Guard feature changes the state of the port to a “root inconsistent” STP
state. This state varies depending on the spanning tree designation. For
MSTP, this is a discarding state. For more information about this
command, see “SPANNING-TREE GUARD ROOT” on page 867.
Note
This feature is also supported in STP and RSTP.