DES-3550 Layer 2 Fast Ethernet Switch User’s Guide
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RSTP is capable of more rapid transition to a forwarding state; it no longer relies on timer
configurations. RSTP compliant bridges are sensitive to feedback from other RSTP compliant
bridge links. Ports do not need to wait for the topology to stabilize before transitioning to a
forwarding state. In order to allow this rapid transition, the protocol introduces two new
variables: the edge port and the point-to-point (P2P) port.
Edge Port
The edge port is a configurable designation used for a port that is directly connected to a
segment where a loop cannot be created. An example would be a port connected directly to a
single workstation. Ports that are designated as edge ports transition to a forwarding state
immediately without going through the listening and learning states. An edge port loses its
status if it receives a BPDU packet, immediately becoming a normal spanning tree port.
P2P Port
A P2P port is also capable of rapid transition. P2P ports may be used to connect to other
bridges. Under RSTP, all ports operating in full-duplex mode are considered to be P2P ports,
unless manually overridden through configuration.
802.1d/802.1w Compatibility
RSTP can interoperate with legacy equipment and is capable of automatically adjusting
BPDU packets to 802.1d format when necessary. However, any segment using 802.1 STP will
not benefit from the rapid transition and rapid topology change detection of RSTP. The
protocol also provides for a variable used for migration in the event that legacy equipment on
a segment is updated to use RSTP.
STP Switch Settings
The Spanning Tree Protocol (STP) operates on two levels. On the switch level, the settings are
globally implemented. On the port level, the settings are implemented on a per user-defined
group of ports basis. To open the following window, open the Spanning Tree folder in the
Configuration menu and click the STP Switch Settings link.
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