For an Ethernet network to function properly, only one active path must exist between two stations. Multiple active paths between stations in a bridged network can cause loops in which Ethernet frames can endlessly circulate. STP can logically break such loops and prevent looping traffic from clogging the network. The dynamic control of the topology provides continued network operation in the presence of redundant or unintended looping paths.
Rapid spanning tree is a link management protocol that provides path redundancy while preventing undesirable loops in the network, such as multiple active paths between stations by forcing redundant paths into a standby or blocked state.PVRST+, which is supported in this release of the switch, is an enhancement of RSTP that works in conjunction with VLANs to provide better control over traffic in the network. A separate spanning tree is maintained for each active VLAN in the network, providing load balancing through multiple instances of the spanning tree, fault tolerance (because failure of one spanning tree instance does not affect other spanning trees), and rapid reconfiguration support through the RSTP.
Refer to the Sun Ethernet Fabric Operating System PVRST+ Administration Guide for more information about this feature.