3Com SuperStack 4 Configuration Manual page 230

242 C 10: RSTP C
HAPTER
Implement RSTP on the
Switch
ONFIGURATION
designated port begin to send data again. That is, the root port and designated
port should undergo a transitional state for a period of Forward Delay before they
enter the forwarding state.
The Switch implements the Rapid Spanning Tree Protocol (RSTP), an enhanced
form of STP. The Forward Delay for the root ports and designated ports to enter
forwarding state is greatly reduced in certain conditions, thereby shortening the
time period for stabilizing the network topology.
To achieve the rapid transition of the root port state, the following requirement
should be met: The old root port on this Switch has stopped data forwarding and
the designated port in the upstream has begun forwarding data.
The conditions for rapid state transition of the designated port are:
The port is an edge port that does not connect with any Switch directly or
■
indirectly. If the designated port is an edge port, it can Switch to forwarding
state directly without immediately forwarding data.
The port is connected with the point-to-point link, that is, it is the master port
■
in aggregation ports or full duplex port. It is feasible to configure a
point-to-point connection. However, errors may occur and therefore this
configuration is not recommended. If the designated port is connected with
the point-to-point link, it can enter the forwarding state right after
handshaking with the downstream Switch and receiving the response.
The Switch that uses RSTP is compatible with the one using STP. Both protocol
packets can be identified by the Switch running RSTP and used in spanning tree
calculation.
In a Switch equipped with the XRN feature, RSTP has the following characteristics:
1) Processing the whole Fabric as a node;
2) Participation of all ports except those used as Fabric ports in role selection;
3) A single root port and bridge id for the whole Fabric;
4) Distributed saving of RSTP port information