Overriding Spanning Tree Configurations

About this task

To configure the port channel's spanning tree configuration:

Procedure

  1. Select the Spanning Tree tab.
    Click to expand in new window
    Port Channels - Spanning Tree Screen
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  2. Define or override the following PortFast parameters for the port channel‘s MSTP configuration:

    Enable PortFast

    Select this option to enable drop-down menus for the Enable PortFast BPDU Filter and Enable PortFast BPDU Guard options.

    PortFast reduces the time required for a port to complete a MSTP state change from Blocked to Forward. PortFast must only be enabled on ports on the wireless controller directly connected to a server/workstation and not another hub or controller. PortFast can be left unconfigured on an access point.

    This option is disabled by default.

    Enable PortFast BPDU Filter

    Enable PortFast to invoke a BPDU filter for this portfast enabled port channel. Enabling the BPDU filter feature ensures this port channel does not transmit or receive any BPDUs. The options are: Default, Enable and Disable.

    • Default — This is the default setting. This option makes the bridge BPDU filter value to take effect.

    • Enable — Enables BPDU filtering.

    • Disable — Disables BPDU filtering.

    Enable PortFast BPDU Guard

    Enable PortFast to invoke a BPDU guard for this portfast enabled port channel. Enabling the BPDU guard feature means this port will shutdown on receiving a BPDU. Hence no BPDUs are processed. The options are:

    • Default — This is the default setting. This option makes the bridge BPDU guard value to take effect.

    • Enable — Enables shutting down of port.

    • Disable — Disables shutting down of port.
  3. Set or override the following MSTP Configuration parameters for the port channel:

    Link Type

    Select either Point-to-Point or Shared. When Point-to-Point is selected, the port is treated as connected to a point-to-point link. Selecting Shared means this port should be treated as having a shared connection.

    Note:

    A port connected to a hub is on a Shared link. Whereas, a port connected to a controller or service platform is a Point-to-Point link.

    The default setting is Point-to-Point.

    Cisco MSTP Interoperability

    Enable or Disable interoperability with Cisco‘s version of MSTP over the port. Cisco's version of MSTP is incompatible with standard MSTP. This setting is disabled by default.

    Force Protocol Version

    Set the protocol version to either STP(0), Not Supported(1), RSTP(2), or MSTP(3). MSTP(3) is the default setting.

    Guard

    Determines whether the port channel enforces root bridge placement. Setting the guard to Root ensures the port is a designated port. Typically, each guard root port is a designated port, unless two or more ports (within the root bridge) are connected together. If the bridge receives superior (BPDUs) on a guard root-enabled port, the guard root moves the port to a root-inconsistent STP state. This state is equivalent to a listening state. No data is forwarded across the port. Thus, the guard root enforces the root bridge position.
  4. Refer to the Spanning Tree Port Cost table.

    Define or override an Instance Index using the spinner control, and set its corresponding cost in the Cost column. The default path cost depends on the user defined port speed. The cost helps determine the role of the port channel in the MSTP network.

    The designated cost is the cost for a packet to travel from this port to the root in the MSTP configuration. The slower the media, higher the cost.

    Table 1. Spanning Tree Port Cost

    Speed

    Default Path Cost

    <=100,000 bits/sec

    200000000

    <=1,000,000 bits/sec

    20000000

    <=10,000,000 bits/sec

    2000000

    <=100,000,000 bits/sec

    200000

    <=1,000,000,000 bits/sec

    20000

    <=10,000,000,000 bits/sec

    2000

    <=100,000,000,000 bits/sec

    200

    <=1,000,000,000,000 bits/sec

    20

    >1,000,000,000,000 bits/sec

    2

    Select + Add Row as needed to include additional indexes.

  5. Refer to the Spanning Tree Port Priority table.

    Define or override an Instance Index using the spinner control, then set the Priority. The lower the priority, the greater likelihood of the port becoming a designated port.

    Select + Add Row as needed to include additional indexes.

  6. Click OK to save the changes and overrides made to the Ethernet port's Spanning Tree configuration.

    Click Reset to revert to the last saved configuration.

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