Once the Root Bridge (Switch) is elected, every other Switch in the network must select a single port on it to reach the Root Bridge (Switch). The single selected port on a Switch with least Path Cost to the Root Bridge is called the Root Port. Root Bridge (Switch) will never have a Root Port. Root Bridge is at the Root and therefore there is no need of a Root Port to reach the root.

The above layout of Switches shows that Switch 4 has two ports to reach the Root Bridge. If there are multiple ports present in a Switch to reach the Root Bridge (Switch) Spanning Tree Algorithm must select the best port from them to reach the Root Bridge. Here the port with least path cost (4+4=8) is marked as Root Port.

 

Related Topics...

• What is Broadcast Storm

• What is Layer 2 Switching loop

• What is Spanning Tree Protocol (STP)

• What is Bridge Protocol Data Unit (BPDU) frame

• Bridge Protocol Data Unit (BPDU) Frame Format

• What is a Root Bridge (Switch)

• What are Port Cost, Port Priority and Path Cost Values

• How Spanning Tree Protocol (STP) select Root Port

• What is a Designated Port

• How Spanning Tree Protocol (STP) select Designated Port

• Difference between Root Port and Designated Port

• Spanning Tree Port States

• Topology Changes in Spanning Tree Protocol (STP)

• Spanning Tree Protocol (STP) Convergence

• What is Spanning Tree Protocol (STP) PortFast

• How to configure and verify Spanning Tree Protocol (STP) PortFast

• How to enable or disable Spanning Tree Protocol (STP)

• What is Rapid Spanning Tree Protocol (RSTP)

• Difference between Spanning Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP)

• Per-VLAN Spanning Tree (PVST) and Per-VLAN Spanning Tree Plus (PVST+)