H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 196)

20-38
ports as non-edge ports and start a new spanning tree calculation process. This will cause 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, network instability
will occur.
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 will close
these ports and notify the NMS that these ports have been closed by MSTP. Those ports closed thereby
can be restored only by the network administers.
It is recommended that you enable the BPDU guard on your device.
Follow these steps to enable BPDU guard:
To do... Use the command... Remarks
Enter system view system-view —
Enable the BPDU guard function
on the device
stp bpdu-protection
Required
Disabled by default
Enabling Root Guard
The root bridge and secondary root bridge of a panning tree should be located in the same MST region.
Especially for the CIST, the root bridge and secondary root bridge are generally put in a high-bandwidth
core region during network design. However, due to possible configuration errors or malicious attacks in
the network, the legal root bridge may receive a configuration BPDU with a higher priority. In this case,
the current, legal root bridge will be superseded by another device, causing undesired change of the
network topology. As a result of this kind of illegal topology change, the traffic that should go over
high-speed links is drawn to low-speed links, resulting in network congestion.
To prevent this situation from happening, MSTP provides the root guard function to protect the root
bridge. If the root guard function is enabled on a port, this port will keep playing the role of designated
port on all MST instances. Once this port receives a configuration BPDU with a higher priority from an
MST instance, it immediately sets that instance port to the listening state, without forwarding the packet
(this is equivalent to disconnecting the link connected with this port). If the port receives no BPDUs with
a higher priority within twice the forwarding delay, the port will revert to its original state.
It is recommended that you enable the root guard feature on your device.
Follow these steps to enable root guard: