TP-Link T2600G-18TSTL-SG3216 T2600G-18TSUN V1 Configuration Guide - Page 321

Configuring Spanning Tree Spanning Tree In RSTP/MSTP, the alternate port is the backup for the root port. It is blocked when the root port works normally. Once the root port fails, the alternate port will become the new root port. In STP, the alternate port is always blocked.  Backup Port If a port is not selected as the designated port for it receives better BPDUs from the switch it belongs to, it will become an backup port. In RSTP/MSTP, the backup port is the backup for the designated port. It is blocked when the designated port works normally. Once the root port fails, the backup port will become the new designated port. In STP, the backup port is always blocked.  Disable Port The disconnected port with spanning tree function enabled . Port Status Generally, in STP, the port status includes: Blocking, Listening, Learning, Forwarding and Disabled.  Blocking In this status, the port receives and sends BPDUs. The other packets are dropped.  Listening In this status, the port receives and sends BPDUs. The other packets are dropped.  Learning In this status, the port receives and sends BPDUs. It also receives the other user packets to update its MAC address table, but doesn't forward them.  Forwarding In this status, the port receives and sends BPDUs. It also receives the other user packets to update its MAC address table, and forwards them.  Disabled In this status, the port is not participating in the spanning tree, and drops all the packets it receives. In RSTP/MSTP, the port status includes: Discarding, Learning and Forwarding. The Discarding status is the grouping of STP's Blocking, Listening and Disabled, and the Configuration Guide 291