1.STP is used to avoid a data link layer protocol logic loops occur. Device running STP discover loops by exchanging information, by blocking specific ports will have to be modified to the network structure a loop-free tree structure. Moreover, when the network fails, STP can quickly find the failed link, quick to find another path for data transmission.
2. STP running on the switch by exchanging information of the BPDU (Bridge Protocol Data Unit), the root switch election, and then each non-root switch for selecting the root port in communication with the root switch, after which each select network to forward the data to the designated port root switch, the last remaining port is blocked.