H3C Technologies H3C S10500 Series Switches - Manual (Page 107)

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To do... Use the command... Remarks
Enable the BPDU guard function for the
device
stp bpdu-protection
Required
Disabled by default.
NOTE:
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, due to 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 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 plays the role of designated port on all MSTIs. After this port receives a
configuration BPDU with a higher priority from an MSTI, it immediately sets that port to the 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.
Configure root guard on a designated port.
Follow these steps to enable root guard:
To do... Use the command... Remarks
Enter system view system-view —
Enter Layer 2 Ethernet
interface view or Layer 2
aggregate interface view
interface interface-type
interface-number
Enter interface
view or port
group view
Enter port group view
port-group manual
port-group-name
Required
Use either command.
Enable the root guard function for the port(s) stp root-protection
Required
Disabled by default.
NOTE:
You cannot configure root guard and loop guard on a port at the same time.
Enabling loop guard
A device that keeps receiving BPDUs from the upstream device can maintain the state of the root port and
blocked ports. However, link congestion or unidirectional link failures might cause these ports to fail to
receive BPDUs from the upstream devices. The device will reselect the port roles: Those ports in
forwarding state that failed to receive upstream BPDUs will become designated ports, and the blocked
ports will transition to the forwarding state, resulting in loops in the switched network. The loop guard
function can suppress the occurrence of such loops.
The initial state of a loop guard-enabled port is discarding in every MSTI. When the port receives BPDUs,
its state transitions normally. Otherwise, it stays in the discarding state to prevent temporary loops.