Spanning Tree Protocol (IEEE Standard 802.1D) was made to prevent loops in switched networks

STP Port States

• Blocking - not forwarding to prevent a loop
• Listening - not forwarding and cleaning the MAC table
• Learning - not forwarding and adding to the MAC table
• Forwarding - data passes through and is fully operational

Ports

• Root - Interface that is ultimately connected to the network’s single Root Bridge
• Designated - Any other port that is not directly connected to the Root but can forward traffic
• Blocked - Ports that do not forward traffic

If an interface goes down, STP will reconfigure the ports on the network

RSTP (802.1w)

Rapid STP

Faster convergence: 30-50s -> 6s

• Faster recovery from failure

Backwards comparable with 802.1D STP