Difference between STP and RSTP

Difference between STP and RSTP

IEEE improved the 802.1d protocol with the definition of the Rapid Spanning Tree Protocol (RSTP), as defined in standard 802.1w.

RSTP works like STP in several ways:

* It elects the root switch using the same parameters and tiebreakers.

* It elects the root port on nonroot switches with the same rules.

* It elects designated ports on each LAN segment with the same rules.

* It places each port in either Forwarding or Blocking State, although RSTP calls the Blocking State the Discarding State.

RSTP can work alongside STP switches, with RSTP features working on switches that support it and STP working on switches that support only STP.

The main reason for the creation of RSTP was an issue of convergence.  STP takes 50 seconds with the default settings.  RSTP improves convergence.

RSTP improves convergence by eliminating or significantly reducing the waiting periods that STP needs to avoid loops during convergence.  STP waits MaxAge (Default 20 seconds) before reacting to some events, whereas RSTP only has to wait 3*Hello (default 6 seconds).  RSTP eliminates the forward delay (default 15 seconds) time in both Listening and Learning States.

RSTP convergence times are typically less than 10 seconds.  They can be as low as 1 to 2 seconds.