24-Port Managed Gigabit Switch
6. 802.1w Rapid Spanning Tree
The Rapid Spanning Tree Protocol (RSTP) is an IEEE standard,
802.1w, that is interoperable with 802.1d and an extension to it.
With RSTP, there are only three port states: discarding, learning
and forwarding. RSTP can operate with legacy equipment
implementing IEEE 802.1d; however the advantages of using RSTP
will be lost. RSTP was developed in order to overcome some
limitations of STP that impede the function of some recent
Switching innovations, in particular, certain Layer 3 functions that
are increasingly handled by Ethernet Switches. The basic function
and much of the terminology is the same as STP. Most of the
settings configured for STP are also used for RSTP. With RSTP,
there are still root and designated ports, performing the same roles
as those in 802.1d. However, RSTP adds two additional port types:
alternate ports and backup ports. An alternate port is port that has
an alternative path or paths to root but is currently in a discarding
state. A backup port is a port on a segment that could be used to
reach the root switch, but there is already an active designated port
for segment. The best way to look at this is that an alternate port is
a secondary, unused root port, and a backup port is a secondary,
unused designated port. Another feature introduced in 802.1w is
rapid transition. Rapid transition can only take place in RSTP for
edge ports and links that are point-to-point.
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