Spanning-Tree Operation802.1D Spanning-Tree Protocol (STP)You can also include STP general parameters in this command. See “Reconfiguring General STP Operation on the Switch” on page 6-26.For example, the following configures ports C5 and C6 to a path cost of 15, apriority of 100, and fast mode:HPswitch(config)# spanning-tree c5-c6 path-cost 15 priority 100 mode fasSTP Fast ModeFor standard STP operation, when a network connection is established on adevice that is running STP, the port used for the connection goes through asequence of states (Listening and Learning) before getting to its final state(Forwarding or Blocking, as determined by the STP negotiation). Thissequence takes two times the forward delay value configured for the switch.The default is 15 seconds on HP switches, per the IEEE 802.1D standardrecommendation, resulting in a total STP negotiation time of 30 seconds. Eachswitch port goes through this start-up sequence whenever the network connection is established on the port. This includes, for example, when the switchor connected device is powered up, or the network cable is connected.A problem can arise from this long STP start-up sequence because some endnodes are configured to automatically try to access a network server when-ever the end node detects a network connection. Typical server accessincludes to Novell servers, DHCP servers, and X terminal servers. If the serveraccess is attempted during the time that the switch port is negotiating its STPstate, the server access will fail. To provide support for this end node behavior,the switches covered by this manual offer a configuration mode, called “FastMode”, that causes the switch port to skip the standard STP start-up sequenceand put the port directly into the “Forwarding” state, thus allowing the serveraccess request to be forwarded when the end node needs it.If you encounter end nodes that repeatedly indicate server access failure whenattempting to bring up their network connection, and you have enabled STPon the switch, try changing the configuration of the switch ports associatedwith those end nodes to STP Fast Mode.C a u t i o n The Fast Mode configuration should be used only on switch ports connectedto end nodes. Changing the Mode to Fast on ports connected to hubs, switches,or routers may cause loops in your network that STP may not be able toimmediately detect, in all cases. This will cause temporary loops in yournetwork. After the fast start-up sequence, though, the switch ports operateaccording to the STP standard, and will adjust their state to eliminate continuing network loops.6-28
