Configuring protection functions
An MSTP-enabled device supports the following protection functions:
MSTP has been correctly configured on the device.
Enabling BPDU guard
For access layer devices, the access ports can directly connect to the user terminals (such as PCs) or file
servers. The access ports are configured as edge ports to allow rapid transition. When these ports
receive configuration BPDUs, the system automatically sets these ports as non-edge ports and starts a
new spanning tree calculation process. This causes a change of network topology. Under normal
conditions, these ports should not receive configuration BPDUs. However, if someone forges
configuration BPDUs maliciously to attack the devices, the network will become unstable.
MSTP provides the BPDU guard function to protect the system against such attacks. With the BPDU guard
function enabled on the devices, when edge ports receive configuration BPDUs, MSTP closes these ports
and notifies the NMS that these ports have been closed by MSTP. The device will reactivate the closed
ports after a detection interval. For more information about this detection interval, see the Fundamentals
Make this configuration on a device with edge ports configured.
Follow these steps to enable BPDU guard:
Enter system view
Enable the BPDU guard function for
BPDU guard does not take effect on loopback testing-enabled ports. For more information about loopback
testing, see the chapter "Ethernet interface configuration."
Enabling root guard
The root bridge and secondary root bridge of a spanning tree should be located in the same MST region.
Especially for the CIST, the root bridge and secondary root bridge are put in a high-bandwidth core
region during network design. However, because of possible configuration errors or malicious attacks in
the network, the legal root bridge might receive a configuration BPDU with a higher priority. Another
device will supersede the current legal root bridge, causing an undesired change of the network topology.
The traffic that should go over high-speed links is switched to low-speed links, resulting in network
To prevent this situation, MSTP provides the root guard function. If the root guard function is enabled on
a port of a root bridge, this port will keep playing the role of designated port on all MSTIs. After this port
Use the command...
Disabled by default.