Spanning Tree Protocol (STP)

Spanning Tree Protocol (STP)

Spanning-Tree Port States

The ports on a bridge or switch running STP can transition through five different states:

Blocking A blocked port won’t forward frames; it just listens to BPDUs. The purpose of the

blocking state is to prevent the use of looped paths. All ports are in blocking state by default

when the switch is powered up.

Listening The port listens to BPDUs to make sure no loops occur on the network before passing

data frames. A port in listening state prepares to forward data frames without populating

the MAC address table.

Learning The switch port listens to BPDUs and learns all the paths in the switched network.

A port in learning state populates the MAC address table but doesn’t forward data frames.

Forwarding The port sends and receives all data frames on the bridged port. If the port is still

a designated or root port at the end of the Learning state, it enters this state.

Disabled A port in the disabled state (administratively) does not participate in the frame forwarding