H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 93)

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Configuration prerequisites
Configure the spanning tree feature correctly 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 start 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 becomes instable.
The spanning tree protocol 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,
the system closes these ports and notifies the NMS that these ports have been closed by the spanning tree
protocol. The closed ports are re-activated by the device after a detection interval. For more information
about this detection interval, see Fundamentals Configuration Guide.
Make this configuration on a device with edge ports configured.
To enable BPDU guard:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enable the BPDU guard
function for the device.
stp bpdu-protection Disabled by default.
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, due to possible configuration errors or malicious attacks in the
network, the legal root bridge may receive a configuration BPDU with a higher priority. The current legal
root bridge is superseded by another device, causing an undesired change of the network topology. As
a result, the traffic that should go over high-speed links is switched to low-speed links, resulting in network
congestion.
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 keeps playing the role of designated port on all MSTIs. Once this port
receives a configuration BPDU with a higher priority from an MSTI, it immediately sets that port to
listening state in the MSTI, without forwarding the packet (this is equivalent to disconnecting the link
connected with this port in the MSTI). If the port receives no BPDUs with a higher priority within twice the
forwarding delay, it reverts to its original state.
Make this configuration on a designated port.
To enable root guard:
Step Command Remarks
1. Enter system view. system-view N/A