Owners manual

DGS-1510 Series Gigabit Ethernet SmartPro Switch CLI Reference Guide
576
Interface Configuration Mode.
Command Default Level
Level: 12.
Usage Guideline
In the RSTP or STP-compatible mode, the administrative path cost is used by the single spanning-tree to
accumulate the path cost to reach the Root. In the MSTP mode, the administrative path cost is used by
the CIST regional root to accumulate the path cost to reach the CIST root.
Example
This example shows how to configure the port cost to 20000 for Ethernet interface eth1/0/7.
Switch# configure terminal
Switch(config)# interface eth1/0/7
Switch(config-if)# spanning-tree cost 20000
Switch(config-if)#
61-9 spanning-tree guard root
This command is used to enable the root guard mode. To return to the default settings, use the no form
of this command.
spanning-tree guard root
no spanning-tree guard root
Parameters
None.
Default
By default, this option is disabled.
Command Mode
Interface Configuration Mode.
Command Default Level
Level: 12.
Usage Guideline
BPDU guard prevents a port from becoming a root port. This feature is useful for the service provider to
prevent external bridges to a core region of the network influencing the spanning tree active topology,
possibly because those bridges are not under the full control of the administrator.
When a port is guarded from becoming a root port, the port will only play the role as a designated port. If
the port receives the configuration BPDU with a higher priority, the port will change to the alternate port,
which is in the blocking state. The received superior factor will not participate in the STP computation.
The port will listen for BPDUs on the link. If the port times out the received superior BPDU, it will change
to the designated port role.
When a port changes to the alternate port state, due to the root guard, a system message will be
generated. This configuration will take effect for all the spanning-tree versions.
Example
This example shows how to configure to prevent Ethernet interface eth3/0/1 from being a root port.