RSTP Link and Edge Types Port States Roles and Convergence

RSTP Link and Edge Types Port States Roles and Convergence

Rapid Spanning Tree Protocol (RSTP) is an evolution of the original Spanning Tree Protocol (STP) that provides faster convergence times and improved network efficiency. In RSTP, the network topology is represented as a spanning tree with the switches as nodes and the links between them as edges.

RSTP introduces two types of ports: edge ports and link-type ports. Edge ports are used for directly connecting end devices, such as computers or servers, to a switch. They are configured with PortFast or similar features, which bypass the STP listening and learning states to speed up the process of connecting devices to the network. Link-type ports are used for inter-switch connections and operate in one of three states: discarding, learning, or forwarding.

RSTP has three port states: discarding, learning, and forwarding. In the discarding state, a port does not forward frames but listens for BPDU frames from the root bridge. In the learning state, a port starts to learn MAC addresses and still does not forward frames. In the forwarding state, a port forwards frames and is fully operational.

RSTP also introduces the concept of roles for ports. The root port is the port that has the lowest path cost to the root bridge. The designated port is the port that has been selected as the forwarding port for a segment. The alternate port is a backup to the root port and the backup designated port is a backup to the designated port. RSTP uses several mechanisms to achieve faster convergence times than STP. One such mechanism is the Rapid Convergence feature, which detects topology changes and quickly transitions the network to a new topology. Another mechanism is the Backup Link feature, which provides an alternate path in case of a link failure.

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