1. Insufficiency of STP
Although the STP protocol can solve the loop problem, the convergence of the network topology is slow. If the topology structure in the network changes frequently, the network will frequently lose reachability, resulting in frequent communication interruptions.
Insufficient point 1 : STP does not distinguish between port status and port role in detail.
From the user's point of view , there is no difference between Listening, Learning, and Blocking states, and user traffic is not forwarded in the same way.
From the perspective of data configuration , the most essential difference between ports is not the status of the ports, but the role of the ports. Because the root port and the designated port can both be in the Listening state or both in the Forwarding state.
Disadvantage 2 : The STP algorithm is a passive algorithm, relying on timers to wait for topology changes to be judged, and the convergence speed is slow.
Disadvantage 3 : The STP algorithm requires that in a stable topology, the root bridge actively sends out a configuration BPDU message, and other devices process the configuration BPDU after receiving it, and then pass it to the entire STP network. This is also one of the main reasons for slow topology convergence.
2. The improvement of RSTP to STP:
1. Refinement of port roles:
Compared with STP, RSTP adds two types of port roles, and there are four types in total: root port, designated port, alternate port, and backup port.
The description of Alternate port and Backup port is as follows:
① From the perspective of configuring BPDU message sending:
The alternate port is the port that is blocked due to learning configuration BPDU packets sent by other bridges.
The backup port is the port that is blocked because it learns the configuration BPDU message sent by itself.