As the Internet grew exponentially in the early 1990s, the size of routing tables maintained by Internet routers grew under IP address. Therefore, IETF introduced CIDR in RFC 1517 in 1993.
Standard Spanning Tree Protocol (802.1D) is a protocol specific to Cisco Switches and was developed to prevent loops that occur on the network. In the link or the cable failure that occurs on the network configured the Spanning Tree Protocol, it is calculated the routes for the packet outgoing to the destination.
The STP protocol OSI model was developed to block Loops in layer 2. STP UplinkFast were developed that STP convergence takes much time.
When a computer or server is connected to a Switch port, it can access the network and communicate with other devices. Layer 2 Switches cause network Loops, which can be prevented by the STP protocol.