3Com Switch 8800 Configuration Guide Chapter 38 MSTP Region-configuration38-24I. Configuration in system viewPerform the following configuration in system view.Table 38-15 Configure the path cost of a portOperation CommandConfigure the path cost of a port. stp interface interface-list [ instanceinstance-id ] cost costRestore the default path cost of a port. undo stp interface interface-list[ instance instance-id ] costII. Configuration in Ethernet port viewPerform the following configuration in Ethernet port view.Table 38-16 Configure the path cost of a portOperation CommandConfigure the path cost of a port stp [ instance instance-id ] cost costRestore the default path cost of a port. undo stp [ instance instance-id ] costYou can configure the path cost of a port with either of the earlier-mentioned measures.Upon the change of path cost of a port, MSTP will recalculate the port role and transitthe state. When instance-id takes 0, it indicates to set the path cost on the CIST.By default, MSTP is responsible for calculating the path cost of a port.38.2.12 STP Path Cost Calculation Standards on STP portThe Switch 8800 uses its own legacy path calculation but both DOT1T andDOT1D-1998 path cost calculation can be used, as well. By default, the DOT1T isapplied.The port rate must be obtained first before calculating the path cost of a port as the pathcost is associated with the port rate. The three standards use their own way to work outthe port rate, based on which each standard calculates the path cost of the by certainalgorithm.I. DOT1T calculation standard1) Calculating the ratez Aggregation portThe rate of either a primary or a secondary port in an aggregation port group is the sumof the port rates in the group. If a port is down, the rate is 0.z Non-aggregation port
