3Com 2816-SFP Plus (3C16485) User Manual

Also see for Baseline 2816: Product guide Datasheet Datasheet Datasheet Datasheet

3Com 2816-SFP Plus (3C16485) User Manual Manual pdf 35 page image

Spanning TreeThis administrative tool supports the configuration of the Switchto forward, or block and discard 802.1D spanning tree BPDUpackets.Spanning tree is a bridge-based system for providing faulttolerance on networks and can be used to detect and disablenetwork loops. The spanning tree ensures that the optimal pathis maintained between spanning tree-compliant networkeddevices by:■ Disabling redundant paths when the main paths areoperational.■ Enabling redundant paths if the main paths fail.Spanning tree uses a distributed algorithm to select a bridgingdevice that serves as the root of the spanning tree network. Thebridging device known as the Root Bridge generates BPDUs(Bridge Protocol Data Units) on all ports at a regular intervalknown as the Hello Time. All other spanning tree-compliantdevices on the network have a designated Root Port. This is thePort nearest the Root Bridge and it is used for receiving theBPDUs initiated by the Root Bridge. If a bridge does not get aHello BPDU after a predetermined interval, the bridge assumesthat the link to the Root Bridge is down. This bridge will theninitiate negotiations with other bridges to reconfigure thenetwork to reestablish a valid network topology.After all the bridges on the network have determined theconfiguration of their ports, each bridge only forwards trafficbetween the Root Port and the ports that are the DesignatedBridge Ports for each network segment. All other ports areblocked, which means that they are prevented from forwardingtraffic.Figure 26 Spanning Tree Screen■ Forward — Spanning tree BPDU packets received on a portare forwarded to all other ports.■ Block and Discard — Spanning tree BPDUs received on a portare dropped. The Switch does not forward BPDUs to otherports.The Switch does not participate as a bridge node in the spanningtree, it can only be configured to forward or block spanning treeBPDUs. If the Switch is connected to other bridging devices, suchas switches, that are part of the spanning tree network, set theSwitch to "Forward." If the Switch is connected only toworkstations, it can be set to "Block and Discard."