Topology Change and Topology Change Detection
Set Spanning Tree Compatibility to STP
Restore Spanning Tree Compatibility
Restore the Default Bridge Priority
Configuring the STP Port Priority
Port Priority Configuration Topology Example
Restore the Default Port Priority
Configuring the Spanning Tree Link Type
Spanning Tree Link Type Overview
Configure the Interface Link Type
Restore the Default Interface Link Type
Configuring the Spanning Tree Portfast Port
Spanning Tree Portfast Port Overview
Restore the Default Portfast Port
Configuring Spanning Tree Timers
Restore the Default Timer Values
Configuring the Pseudo Root ID
Display Spanning Tree Information for Active Ports
Display Detailed Spanning Tree Information
Display the Spanning Tree Port-Specification Configuration
Display a Summary of the Spanning Tree Information for the Configuration
Specify MST Forward Time, Hello Time, and Max Age
Set the Spanning Tree Operating Mode
Specify MST Mode Configurations
Configuring the Spanning Tree Switch Priority
Configure the Spanning Tree Switch Priority
Restore the Default Spanning Tree Priority
Configure MST Properties of an Interface
Restore the Default MSTP Priority
Configuring the Interval Between Generation of Configuration Messages
Configure the MST Interval Between Generation of Configuration Messages
Restore the Default Interval Between Generation of Configuration Messages
Configuring the Maximum Hop Count
Configure the Maximum Hop Count
Restore the Default Maximum Hop Count
Configuring the Pseudo Root ID
Configuring Features Common to RSTP and MSTP
Clear Spanning Tree MSTP Counters
Configuring the Transit Hold Count
Configure the Transmit Hold Count
Restore the Default Transmit Hold Count Value
Configuring the Dynamic Path Cost
Dynamic Path Cost Topology Example
Configure the Dynamic Path Cost
Configure the Dynamic Path Cost in an Aggregate Port
Disable the Dynamic Path Cost Calculation
Configure the Dynamic Path Cost Lag Speed in an Aggregate Port
Disable the Dynamic Path Cost Lag Speed Calculation
Enable Spanning Tree Loop Guard
Show Spanning Tree Performance Data
Configuring Automatic Detection of Edge Devices or Bridges
Configure Automatic Detection of Edge Devices or Bridges
Disable Automatic Detection of Edge Devices or Bridges
Configuring the Restricted Role
Configuring the Topology Change
Restart the Protocol Migration Process
Configuring the Spanning Tree BPDU Receive Status
Configure the Spanning Tree BPDU Receive Status
Disable the Spanning Tree BPDU Receive Status
Configuring the Spanning Tree BPDU Transmit Status
Configure the Spanning Tree BPDU Transmit Status
Disable the Spanning Tree BPDU Transmit Status
Configuring the Spanning Tree L2GP Status
Configure the Spanning Tree L2GP Status
Display the Spanning Port Information
Display the MST Configuration and Status
Topology After Configuring the Bridge Priority and Port Path Cost in RSTP
In the spanning tree algorithm, a port selected as a designated port waits for 2 x forward-delay (2 x 15) seconds before transitioning to the forwarding state. In RSTP, this port corresponds to a designated role and blocking state.
P0 - Designated port
P1 - New root port
P2 - Alternate port
P3 - Designated port
P4 - Edge port
If a new link is created between root and switch 1, both ports go into a designated blocking state until they receive a BPDU from their counterpart. The proposal bit on the BPDUs is set and sent out only when a designated port is in discarding or learning state. This process occurs for port P0 of the root bridge. Because switch 1 receives superior information, switch 1 immediately knows that port P1 is the new root port. Switch 1 then ensures that all of the ports are in sync with this new information.
A port is in sync only if the port meets one of the following criteria:
The port is in the blocking state.
The port is an edge port.
If an alternate port P2, a designated forwarding port P3, and an edge port P4 exist on switch 1, P2 and P4 already meet one of the listed criteria. To be in sync, switch 1 must block port P3, assigning it the discarding state. If all ports are in sync, switch 1 can unblock its newly selected root port P1 and reply to the root by sending an agreement message. This message is a copy of the proposal BPDU with the agreement bit set instead of the proposal bit. This copy ensures that port P0 knows exactly which proposal that the agreement it receives corresponds to.
When port P0 receives the agreement, port P0 can immediately transition to forwarding. Port P3, which was left in a designated discarding state after the sync, is in exactly the same state as port P0 before receiving the agreement. Port P0 then starts proposing to its neighbor, attempting to quickly transition to forwarding. This handshake mechanism propagates quickly towards the edge of the network, and quickly restores connectivity after a change in the topology.