Operation Manual – MSTPH3C S3100 Series Ethernet Switches Chapter 1 MSTP Configuration1-29Caution:z The forward delay parameter and the network diameter are correlated. Normally, alarge network diameter corresponds to a large forward delay. A too small forwarddelay parameter may result in temporary redundant paths. And a too large forwarddelay parameter may cause a network unable to resume the normal state in timeafter changes occurred to the network. The default value is recommended.z An adequate hello time parameter enables a switch to detect link failures in timewithout occupying too many network resources. And a too small hello timeparameter may result in duplicated configuration BPDUs being sent frequently,which increases the work load of the switches and wastes network resources. Thedefault value is recommended.z As for the max age parameter, if it is too small, network congestion may be falselyregarded as link failures, which results in frequent spanning tree recalculation. If it istoo large, link problems may be unable to be detected in time, which preventsspanning trees being recalculated in time and makes the network less adaptive. Thedefault value is recommended.As for the configuration of the three time-related parameters (that is, the hello time,forward delay, and max age parameters), the following formulas must be met to preventfrequent network jitter.2 x (forward delay – 1 second) >= max ageMax age >= 2 x (hello time + 1 second)You are recommended to specify the network diameter of the switched network and thehello time by using the stp root primary or stp root secondary command. After that,the three proper time-related parameters are determined automatically.II. Configuration example# Configure the forward delay parameter to be 1,600 centiseconds, the hello timeparameter to be 300 centiseconds, and the max age parameter to be 2,100centiseconds (assuming that the current switch operates as the CIST root bridge). system-view[Sysname] stp timer forward-delay 1600[Sysname] stp timer hello 300[Sysname] stp timer max-age 21001.3.10 Configuring the Timeout Time FactorWhen the network topology is stable, a non-root-bridge switch regularly forwardsBPDUs received from the root bridge to its neighboring devices at the interval specified
