RSTP

Rapid Spanning Tree Protocol:

• Faster Convergence than STP
• Can respond to changes within 6 seconds. This is done by detecting root switch failure - or failure of 3 hello times
  
• Edge ports are considered if they have no more LAN's that have no other bridge attached. These go to forwarding state, RSTP monitors the port for BDPU's in case a new bridge is connected, when one is connected the once edge port is no longer a edge port.
• RSTP responds to BPDU's sent from root bridge, STP does not do this. The best RSTP bridge will become the root bridge by means of this proposal, in inferior RSTP bridge will recieve this information and set its ports to discard. An Agreement is sent after this, and the new bridge can now rapidly transition the port to forwarding instead of listening/learning. This cascades up the stack away from the root bridge until the RSTP topology is created.
  
• Backup details of discarded ports, thus creating an avoidance of timeouts
• BPDUs are used in to make a calculation with STA (Spanning Tree Algorithm) to determine the role of a port

Bridge port roles:

• Root - The best port that becomes the forwarder, spawned from nonroot to root
  
• Designated - Forwarding port
  
• Alternate - Different path to root, not the root port
• Backup - Redundant path to segment where another bridge port connects
• Disabled - Not turned on, not necessarily a part of STP

Port states:

• Discarding
• Learning
• Forwarding