max age - how long the configuration is valid (default timer=20 seconds),.hello time - how often BPDUs are going to be sent/relayed (default timer=2 seconds),.Root bridge will impose the timers that other switches will use such as: It will be the reference point from which the loop free topology is computed. Root bridge is the switch that has all ports working in the designated role. Those frames contain multiple parameters that switches are going to process in order to create and maintain loop free topology. I will use both terms interchangeably.Īs soon as you familiarize yourself with STP port roles and port states, it is time to explain how Spanning-Tree Protocol works.Īll switches communicate with one another using special frames called BPDU. Also, the port will process all incoming Ethernet frames and will actively learn MAC addresses from the arriving traffic.īridges and switches are functionally the same devices. Forwarding - The port in this state will forward all Ethernet frames as per switch operation.

This helps avoid too much flooding when the port transition to the forwarding state. If the port transitions to this state (learning), it can stay in this state for 15 seconds by default (forward_delay). It will be learning MAC addresses from the frames arriving at the port in order to populate MAC address table. However, the port will not forward any Ethernet frames yet. Learning - The port in this state already knows its role (root port or designated port ) in the STP domain.The computation of loop free topology takes place in this state. If the port transitions to this state (listening), it can stay in this state for 15 seconds by default (forward_delay). However, the port in this state does NOT learn any MAC addresses, and does NOT forward or process incoming frames either. Listening - The port in this state CAN send and receive the BPDU frames.If the port transitions to this state (blocking), it can stay blocked for 20 seconds by default (max_age). However, the port DOES process BPDU frames received from neighbor switches.

Blocking - The port does NOT forward any Ethernet frames, does NOT accept any Ethernet frames (discards arriving frames), does NOT learn any MAC addresses.

Disabled - The port in this state does not participate in the STP operation (it is shut down).

Packet tracer labs spanning tree