Dell PowerConnect 5548 User Guide - Page 22

Fast Link STP can take 30-60 seconds to converge. During this time, STP detects possible loops, enabling time for status changes to propagate and for relevant devices to respond. This period of 30-60 seconds is considered too long a response time for many applications. The Fast Link option bypasses this delay, and can be used in network topologies, where forwarding loops do not occur. For more information on enabling Fast Link for ports and LAGs, see "STP Port Settings" on page 436 or "Static Addresses" on page 418. IEEE 802.1w Rapid Spanning Tree Spanning Tree takes 30-60 seconds for each host to decide whether its ports are actively forwarding traffic. Rapid Spanning Tree (RSTP) detects uses of network topologies to enable faster convergence, without creating forwarding loops. For more information, see "Spanning Tree" on page 428. IEEE 802.1s Multiple Spanning Tree Multiple Spanning Tree (MSTP) operation maps VLANs into STP instances. MSTP provides a different load balancing scenario. Packets assigned to various VLANs are transmitted along different paths within MSTP Regions (MST Regions). Regions are one or more MSTP bridges by which frames can be transmitted. The standard lets administrators assign VLAN traffic to unique paths. For more information, see "Spanning Tree" on page 428. STP BPDU Guard BPDU Guard is used as a security mechanism, to protect the network from invalid configurations. BPDU Guard is usually used either when fast link ports (ports connected to clients) are enabled or when the STP feature is disabled. When it is enabled on a port, the port is shut down if a BPDU message is received and an appropriate SNMP trap is generated. For more information, see "Spanning Tree" on page 428. 22 Dell PowerConnect 55xx Systems User Guide