H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – MSTP
H3C S7500E Series Ethernet Switches Chapter 1 MSTP Configuration
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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.
 Note:
It is recommended that you enable the root guard feature on your device.
Follow these steps to enable root guard:
To do... Use the command... Remarks
Enter system view
system-view
—
Enter
Ethernet
interface
view
interface interface-type
interface-number
Enter
Ethernet
interface
view or port
group view
Enter port
group view
port-group { manual
port-group-name |
aggregation agg-id }
Required
Use either command.
Configurations made in
Ethernet interface view
will take effect on the
current port only;
configurations made in
port group view will take
effect on all ports in the
port group.
Enable the root guard
function on the port(s)
stp root-protection
Required
Disabled by default
1.8.4 Enabling Loop Guard
By keeping receiving BPDUs from the upstream device, a device can maintain the state
of the root port and other blocked ports. However, due to link congestion or
unidirectional link failures, these ports may fail to receive BPDUs from the upstream
device. In this case, the downstream device will reselect the port roles: those ports
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.
If a loop guard–enabled port fails to receive BPDUs from the upstream device, and if
the port took part in STP calculation, all the instances on the port, no matter what roles
they play, will be set to, and stay in, the Discarding state.