STP - RSTP prerequisites for immediate move to forward state

When employing RSTP as the type of Spanning Tree Protocol (STP), a port will move immediately to the forwarding state only if certain prerequisites are met.

Rapid spanning tree can only put interfaces in the forwarding state really fast on edge ports (portfast) or if the link type is point-to-point.

There are only two link types:

  • Point-to-point (full duplex)
  • Shared (half duplex)

Normally we are using switches, and all our interfaces are configured as full duplex, rapid spanning tree sees these interfaces as point-to-point. If we introduce a hub to our network, we’ll have half duplex, which is seen as a shared interface to rapid spanning tree.