Lenovo RackSwitch G8264 Application Manual page 191

Port Priority
Root Guard
Loop Guard
© Copyright Lenovo 2016
The port priority helps determine which bridge port becomes the root port or the
designated port. The case for the root port is when two switches are connected using
a minimum of two links with the same path‐cost. The case for the designated port is
in a network topology that has multiple bridge ports with the same path‐cost
connected to a single segment, the port with the lowest port priority becomes the
designated port for the segment. Use the following command to configure the port
priority:
RS G8264(config­if)# spanning­tree stp <STG number or range> priority <port
priority>
where priority value is a number from 0 to 240, in increments of 16 (such as 0, 16, 32,
and so on). If the specified priority value is not evenly divisible by 16, the value will
be automatically rounded down to the nearest valid increment whenever manually
changed in the configuration, or whenever a configuration file from a release prior
to ENOS 6.5 is loaded.
The root guard feature provides a way to enforce the root bridge placement in the
network. It keeps a new device from becoming root and thereby forcing STP
re‐convergence. If a root‐guard enabled port detects a root device, that port will be
placed in a blocked state.
You can configure the root guard at the port level using the following commands:
RS G8264(config)# interface port <port number>
RS G8264(config­if)# spanning­tree guard root
The default state is "none", i.e. disabled.
In general, STP resolves redundant network topologies into loop‐free topologies.
The loop guard feature performs additional checking to detect loops that might not
be found using Spanning Tree. STP loop guard ensures that a non‐designated port
does not become a designated port.
To globally enable loop guard, enter the following command:
RS G8264(config)# spanning­tree loopguard
Note: The global loop guard command will be effective on a port only if the
port‐level loop guard command is set to default as shown below:
RS G8264(config)# interface port <port number>
RS G8264(config­if)# no spanning­tree guard
To enable loop guard at the port level, enter the following command:
RS G8264(config)# interface port <port number>
RS G8264(config­if)# spanning­tree guard loop
The default state is "none" (disabled).
Chapter 11: Spanning Tree Protocols
191