Introduction 27Spanning Tree Protocol FeaturesSpanning Tree Now Supports IEEE 802.1Q-2005This version of the IEEE Multiple Spanning Tree Protocol corrects problems associated with the previousversion, provides for faster transition-to-forwarding, and incorporates new features for a port (restrictedrole and restricted TCN).Spanning Tree Enhancements• Loop Guard — This feature prevents a port from erroneously transitioning from blocking state toforwarding when the port stops receiving BPDUs. The port is marked as being in loop-inconsistentstate. In this state, the port does not forward packets. The possible values are Enable or Disable.• TCN Guard — Enabling the TCN Guard feature restricts the port from propagating any topologychange information received through that port. This means that even if a port receives a BPDU withthe topology change flag set to true, the port will not flush its MAC address table and send out a BPDUwith a topology change flag set to true.• Auto Edge — Enabling the Auto Edge feature allows the port to become an edge port if it does not seeBPDUs for some duration.• BPDU Filter — When enabled, this feature filters the BPDU traffic on this port when STP is enabledon this port.• BPDU Flood — When enabled, the BPDU Flood feature floods the BPDU traffic arriving on this portwhen STP is disabled on this port.Spanning Tree Protocol (STP) per Switch802.1d STP is a standard requirement of Layer 2 switches that allows bridges to automatically preventand resolve L2 forwarding loops.For information about configuring Spanning Tree Protocol, see "Configuring the Spanning TreeProtocol."IEEE 802.1w Rapid Spanning TreeRapid Spanning Tree Protocol (RSTP) detects and uses network topologies to enable faster spanning treeconvergence after a topology change, without creating forwarding loops.For information about configuring Rapid Spanning Tree Protocol, see "Rapid Spanning Tree."Multiple Spanning TreeMultiple Spanning Tree (MSTP) operation maps VLANs to spanning tree instances. Packets assigned tovarious VLANs are transmitted along different paths within MSTP Regions (MST Regions). Regions areone or more interconnected MSTP bridges with identical MSTP settings. The MSTP standard letsadministrators assign VLAN traffic to unique paths.For information about configuring Multiple Spanning Tree, see "MSTP Settings."
