H3C S5120-EI Series User Manual

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Enabling Root Guard
We recommend that you enable root guard on a designated port.
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the current legal root bridge will be superseded by another device, causing an undesired change of the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 from happening, MSTP provides the root guard function to protect the root
bridge. 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. Once 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, the port will revert to its original state.
Follow these steps to enable root guard:
To do... Use the command... Remarks
Enter system view
system-view
—
Enter 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.
Configurations made in
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
for the port(s)
stp root-protection
Required
Disabled by default
Enabling Loop Guard
We recommend that you enable loop guard on the root port or an alternate port of a device.

H3C S5120-EI Series Specifications

General

Brand	H3C
Model	S5120-EI Series
Category	Switch
Language	English