Spanning-Tree Protocol is a link management protocol that provides path redundancy while  preventing undesirable loops in the network. For an Ethernet network to function properly， only one active path can exist between two stations. Multiple active paths between stations cause loops in the network. If a loop exists in the network topology， the potential exists for duplication of messages. When loops occur， some switches see stations appear on both sides of the switch. This condition confuses the forwarding algorithm and allows duplicate frames to be forwarded. To provide path redundancy， Spanning-Tree Protocol defines a tree that spans all switches in an extended network. Spanning-Tree Protocol forces certain redundant data paths into a standby （blocked） state. If one network segment in the Spanning-Tree Protocol becomes unreachable， or if Spanning-Tree Protocol costs change， the spanning-tree algorithm reconfigures the spanning-tree topology and reestablishes the link by activating the standby path. Spanning-Tree Protocol operation is transparent to end stations， which are unaware whether they are connected to a single LAN segment or a switched LAN of multiple segments.There is a lab about STP in Cisco CCNP 642-812 / 642- 892 exam. Requirements:  You will configure FastEthernet ports 0/12 through 0/24 for users who belong to VLAN 20. Also, all VLAN and VTP configurations are to be completed in global configuration mode as VLAN database mode is being deprecated by Cisco. You are required to accomplish the following tasks:  1. Ensure the switch does not participate in VTP but forwards VTP advertisements received on trunk ports.  2. Ensure all non-trunking interfaces (Fa0/1 to Fa0/24) transition immediately to the forwarding state of Spanning-Tree.  3. Ensure all FastEthernet interfaces are in a permanent non-trunking mode.  4. Place FastEthernet interfaces 0/12 through 0/24 in VLAN 20