About the Spanning Tree ProtocolThe Spanning Tree Protocol (STP) is used to detect and break circular traffic patterns, or loops. Loops can cause exponential traffic replication resulting in severe network congestion. The GS2000 line card implements the IEEE 802.1D Spanning Tree Protocol. The line card does not interoperate with DEC LANbridge 100 STP. STP eliminates loops by selecting one of the redundant bridges as the primary or root bridge, and maintaining secondary bridges as backups. The root bridge is selected, in part, based on a priority value you can assign to each bridge. STP then selects a root port on each secondary bridge. The root port is selected based on the relative priority of each port, and which port provides access to the root bridge at the least cost. The bridge then enables all root ports for forwarding, and disables other ports to prevent loops. The Spanning Tree Protocol algorithm runs automatically for each VSD you create. Therefore, multiple spanning trees are supported on the bridge. The STP parameters you set, as described in this section, affect all instances of STP. You cannot configure different values for each instance of STP. For more information on Virtual LANs (VLANs), see Chapter 9 of the DIGITAL GIGAswitch GS2000 Line Card Management guide. You can enable and disable STP on a port. You can also set certain parameters that influence selection of the root bridge, the root port, and the frequency with which changes in network topology are detected. For a more detailed discussion of STP concepts, see the DIGITAL VNswitch 900 Series Technical Overview. |