3.2. History of STP
Now that you understand the operation of 802.1d STP and its primary functions, it is time to take a look at the shortcomings of this original standard. Possibly the biggest problems arose around the amount of time it takes to converge the network, to move a port into forwarding state, and to allow a host to send traffic.
Another major issue arose when VLANs were included in the network topology. IEEE 802.1d STP operates at Layer 2. When the switch or bridge topology only had Layer 2 boundaries, 802.1d worked well. It did not have to deal with Layer 3 borders or the possibility of a different topology with each VLAN. Cisco saw many of these needs before an open standard change was made to the protocol.
Cisco saw the need to ...