Spanning Tree Port States

Rapid Spanning Tree 802.1w reduced the number of port states from 5 down to 3 this short blog post details the 5 STP port states for Spanning Tree 802.1d and then Rapid Spanning Tree – as always these posts are purely my study notes which I hope can be of use to somebody else and provides an easy way for me to find them again. i.e I just google Spanning Tree Port States and I can find it again wherever I am!

Spanning Tree 802.1d

1. Disabled – A port in the disabled state does not participate in frame forwarding and is considered non-operational
2. Blocking – During blocking state, the port is listening to and processing BPDUs After 20 seconds, the switch port changes from the blocking state to the listening state.
3. Listening – After blocking, a root port or a designated port will move to a listening state. During the listening state the port discards frames received from the attached network segment it also discards frames switched from other ports for forwarding.  At this state, the port receives BPDUs from the network segment and directs them to the switch system module for processing. After 15 seconds, the switch port moves from the listening state to the learning state.
4. Learning – A port moves into the learning state after the listening state. During the learning state, the port is listening for and processing BPDUs. In the listening state, the port starts to process user frames and starts updating the MAC address table. User frames are not forwarded to the destination. After 15 seconds, the switch port moves from learning to forwarding.
5. Forwarding – Once in the forwarding state the port sends traffic. In a forwarding state, the port will process BPDUs, update its MAC Address table with frames that it receives, and forward user traffic through the port. Forwarding State is the normal operational state.

Spanning Tree 802.1W – reduced the number of port states from 5 to 3 and changed Disabled, Blocking & Listening to Discarding

STP Port State    –   RSTP State
Disabled                         Discarding
Blocking                         Discarding
Listening                        Discarding
Learning                         Learning
Forwarding                   Forwarding

To learn more about Rapid Spanning Tree and the Spanning Tree Port States Cisco’s website is the place to go

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml