Rstp Features

RSTP Features RSTP (Rapid Spanning Tree Protocol) is a high-frequency exam topic within Network Access (20%) — expect multiple choice questions on port roles, port states, and how RSTP converges faster than classic STP. --- ## Why RSTP Exists Classic 802.1D Spanning Tree Protocol (STP) was designed in the 1980s when network convergence speed was not a priority. When a topology change occurred, ports moved through a series of states that could take 30–50 seconds before traffic could flow again. In modern networks, that delay is unacceptable. RSTP (802.1w) was introduced to solve this problem. It converges in seconds rather than tens of seconds by using smarter port roles, active negotiation between switches, and fewer transitional states. Cisco's Rapid PVST+ is the default STP mode on modern Cisco switches and runs a separate instance of RSTP for each VLAN — combining the fast convergence of 802.1w with the per-VLAN flexibility Cisco networks rely on. --- ## RSTP Port Roles RSTP defines five port roles, compared to the simpler role set in classic STP: | Port Role | Description | |---|---| | Root Port | Best path toward the Root Bridge (one per non-root switch) | | Designated Port | Best port on a segment; forwards traffic toward downstream switches | | Alternate Port | Backup path to the Root Bridge; takes over if Root Port fails | | Backup Port | Redundant path on the same shared segment as another designated port on the same switch | | Disabled Port | Administratively shut down; not participating in STP | The Alternate Port is the key innovation for fast convergence. It already knows it is the second-best path to the…