STP Interface Settings

The STP Interface Settings page enables you to configure STP on a per-port basis, and to view the information learned by the protocol, such as the designated bridge.

The defined configuration entered is valid for all flavors of the STP protocol.

To configure STP on an interface, follow these steps:

Procedure

Step 1

Click Spanning Tree > STP Interface Settings.

  • Port Role-Displays the port or LAG role, per port or LAG per instance, assigned by the MSTP algorithm to provide STP path.

    • Root-Forwarding packets through this interface provides the lowest cost path for forwarding packets to the root device.

    • Designated-The interface through which the bridge is connected to the LAN, which provides the lowest root path cost from the LAN to the Root Bridge for the MST instance.

    • Disable-The interface doesn’t participate in the Spanning Tree.

Step 2

Select an interface and click Edit.

Step 3

Enter the parameters

Interface

Select the Port or LAG on which Spanning Tree is configured.

STP

Enables or disables STP on the port.

Edge Port

Enables or disables Fast Link on the port. If Fast Link mode is enabled on a port, the port is automatically set to Forwarding state when the port link is up. Fast Link optimizes the STP protocol convergence. The options are:

  • Enable—Enables Fast Link immediately

  • Auto—Enables Fast Link a few seconds after the interface becomes active. This allows STP to resolve loops before enabling Fast Link

  • Disable—Disables Fast Link

    Note

    It’s recommended to set the value to Auto so that the device sets 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. Edge Port isn’t operational in MSTP mode.

Root Guard

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

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 can’t 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 by selecting Use Default or User Defined and enter a range from 1 - 200000000.

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 0–240, and must be a multiple of 16.

Port State

Displays the current STP state of a port.

  • Disabled—STP is currently disabled on the port. The port forwards traffic while learning MAC addresses.

  • Blocking—The port is currently blocked, and can’t forward traffic (except for BPDU data) or learn MAC addresses.

  • Listening—The port is in Listening mode. The port can’t forward traffic, and can’t learn MAC addresses.

  • Learning—The port is in Learning mode. The port can’t forward traffic, but it can learn new MAC addresses.

  • Forwarding—The port is in Forwarding mode. The port can forward traffic and learn new MAC addresses.

Designated Bridge ID

Displays the bridge priority and the MAC address of the designated bridge

Designated Port ID

Displays the priority and interface of the selected port.

Designated Cost

Displays the cost of the port participating in the STP topology. Ports with a lower cost are less likely to be blocked if STP detects loops.

Forward Transitions

Displays the number of times the port has changed from the Blocking state to Forwarding state.

Speed

Displays the speed of the port.

LAG

Displays the LAG to which the port belongs. If a port is a member of a LAG, the LAG settings override the port settings.

Step 4

Click Apply. The interface settings are written to the Running Configuration file.