UMN:CLI
User Manual
V8102
386
9.4.9
Root Guard
The standard STP does not allow the administrator to enforce the position of the root
bridge, as any bridge in the network with lower bridge ID will take the role of the root
bridge. Root guard feature is designed to provide a way to enforce the root bridge place-
ment in the network. Even if the administrator sets the root bridge priority to zero in an ef-
fort to secure the root bridge position, there is still no guarantee against bridge with priori-
ty zero and a lower MAC address.
Fig. 9.35
Root Guard
Software-based bridge applications launched on PCs or other switches connected by a
customer to a service-provider network can be elected as root switches. If the priority of
bridge B is zero or any value lower than that of the root bridge, device B will be elected as
a root bridge for this VLAN. As a result, network topology could be changed. This may
lead to sub-optimal switching. But, by configuring root guard on switch A, no switches be-
hind the port connecting to switch A can be elected as a root for the service provider
’
s
switch network. In which case, switch A will block the port connecting switch B.
To configure Root-Guard, use the following command.
Command
Mode
Description
spanning-tree guard root
Interface
[XE/GE]
Configures Root Guard on the network.
To delete a configured Root-Guard of specified port, use the following command.
Command
Mode
Description
spanning-tree guard none
Interface
[XE/GE]
Disables Root Guard function.
no spanning-tree guard
Deletes a configured Root Guard, returns to default
configurations.
