As I understood and also simulated, I got that RSTP isn't so rapid unless applying (spanning-tree portfast) and as anyone may knows portfast is the port that ignoring STP easily and so leading to Loops, My question is how in this case loop doesn't happen, is it because the portfast is in inactive (alternate or blocking) state? Any more explanation, It's confusing me.
Thanks in advance
spanning-tree portfast brings an RSTP port into edge mode. In that case, it will not ignore bpdu's but return to the appropriate forwarding, alternate, or blocking state if the port receives a BPDU. RSTP isn't going to be quick in transitioning a port connected to a host very quickly unless it is designated to be an edge port by placing it into portfast. The reason why is because RSTP is backward compatible with STP. When the port comes up and sends RSTP it expects responses. No responses makes RSTP believe it can connected to an STP only switch.