840 | Per-VLAN Spanning Tree Plusw w w . d e l l . c o m | s u p p o r t . d e l l . c o mModify Global PVST+ ParametersThe root bridge sets the values for forward-delay, and hello-time and overwrites the values set on otherPVST+ bridges.• Forward-delay is the amount of time an interface waits in the Listening State and the Learning Statebefore it transitions to the Forwarding State.• Hello-time is the time interval in which the bridge sends Bridge Protocol Data Units (BPDUs).• Max-age is the length of time the bridge maintains configuration information before it refreshes thatinformation by recomputing the PVST+ topology.To change PVST+ parameters, use the following commands on the root bridge:The values for global PVST+ parameters are given in the output of the command show spanning-tree pvst,as shown in Figure 40-4.Modify Interface PVST+ ParametersYou can adjust two interface parameters to increase or decrease the probability that a port becomes aforwarding port:• Port cost is a value that is based on the interface type. The greater the port cost, the less likely the portwill be selected to be a forwarding port.• Port priority influences the likelihood that a port will be selected to be a forwarding port in case thatseveral ports have the same port cost.Task Command Syntax Command ModeChange the forward-delay parameter.• Range: 4 to 30• Default: 15 secondsvlan forward-delay PROTOCOL PVSTChange the hello-time parameter.Note: With large configurations (especially those withmore ports) Dell Force10 recommends that you increasethe hello-time.Range: 1 to 10Default: 2 secondsvlan hello-time PROTOCOL PVSTChange the max-age parameter.Range: 6 to 40Default: 20 secondsvlan max-age PROTOCOL PVST
