Cisco 500 Series Administration Manual page 302

Spanning Tree
Spanning Tree Interface Settings
Cisco 500 Series Managed Switch Administration Guide
It is recommended to set the value to Auto so that the device sets
NOTE
the port to fast link mode if a host is connected to it, or sets it as a regular
STP port if connected to another device. This helps avoid loops.
• Root Guard—Enables or disables Root Guard on the device. The Root
Guard option provides a way to enforce the root bridge placement in the
network.
Root Guard ensures that the port on which this feature is enabled is the
designated port. Normally, all root bridge ports are designated ports, unless
two or more ports of the root bridge are connected. If the bridge receives
superior BPDUs on a Root Guard-enabled port, Root Guard moves this port
to a root-inconsistent STP state. This root-inconsistent state is effectively
equal to a listening state. No traffic is forwarded across this port. In this way,
Root Guard enforces the position of the root bridge.
• BPDU Guard—Enables or disables the Bridge Protocol Data Unit (BPDU)
Guard feature on the port.
The BPDU Guard enables you to enforce the STP domain borders and keep
the active topology predictable. The devices behind the ports that have
BPDU Guard enabled cannot influence the STP topology. At the reception of
BPDUs, the BPDU guard operation disables the port that has BPDU
configured. In this case, a BPDU message is received, and an appropriate
SNMP trap is generated.
• BPDU Handling—Select how BPDU packets are managed when STP is
disabled on the port or the device. BPDUs are used to transmit spanning tree
information.
- Use Global Settings—Select to use the settings defined in the STP
Status and Global Settings page.
- Filtering—Filters BPDU packets when Spanning Tree is disabled on an
interface.
- Flooding—Floods BPDU packets when Spanning Tree is disabled on an
interface.
• Path Cost—Set the port contribution to the root path cost or use the default
cost generated by the system.
• Priority—Set the priority value of the port. The priority value influences the
port choice when a bridge has two ports connected in a loop. The priority is
a value from 0 to 240, set in increments of 16.
• Port State—Displays the current STP state of a port.
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