Top and basic 10 points regarding STP. STP: 1. Spanning Tree Protocol based on IEEE 802.1 D standards. 2. STP is a layer 2 link management protocol that provided path redundancy providing the loop prevention. 3. STP is mainly used for preventing looping or to avoid loops. Provided Network Redundancy so that the Layer 2 switched Network can get recover from failures without the intervention in a timely manner. 4. Uses STP Algorithm which calculates the best layer 2 path and also the best loop free path through a switched layer 2 network. 5. Root Switch is the key Switch in STP role. 6. Switched send and receive layer 2 frames which are called as BPDU (Bridge Protocol Data Units) at regular intervals. Communication is done with BPDU. 7. STP Multi cast address: 01-80-c2-00-00-00 8.Inferior information is discarded and Superior information is Propagated to the network. 9. Bridge ID = 8bytes. (6 - MAC address and 2 - Bridge priority). 10. STP States: a. Disabled -- Administratively Shut down. b. Blocking -- Port cannot received or transmit data and cannot add MAC Address to its table. c. Listening -- Here Switch is elected as Root Switch. d. Learning -- Populating CAM table. (Content Addressable Memory). e. Forwarding -- Sending / Receiving Users Data. There are other STP : PVST+, RPVST+ and MST. PVST+ : Per Vlan Spanning Tree | RPVST+ : Rapid Per Vlan Spanning Tree | MST : Multiple Spanning Tree. Regards, Raja Vuttham.