3Com Switch 7750 SeriesCommand Reference Guide – MSTP Chapter 1 MSTP Configuration Commands1-43As 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 toprevent 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 automatically determined.Related command: stp timer hello, stp timer max-age, and stp bridge-diameter.Example# Set the Forward delay to 2,000 centiseconds.<3Com> system-viewSystem View: return to User View with Ctrl+Z.[3Com] stp timer forward-delay 20001.1.41 stp timer helloSyntaxstp timer hello centi-secondsundo stp timer helloViewSystem viewParametercenti-seconds: Hello time in centiseconds to be set. This argument ranges from 100 to1,000 and defaults to 200.DescriptionUse the stp timer hello command to set the Hello time of the switch.Use the undo stp timer hello command to revert to the default Hello time.A root bridge regularly sends out configuration BPDUs to maintain the existingspanning trees. The Hello time is used to set the sending interval. When a switchbecomes a root bridge, it regularly sends BPDUs at the interval specified by the hellotime you have configured on it. While, the other none-root-bridge switches listen to theBPDUs; if they do not receive a BPDU in a specific period, spanning trees will beregenerated.
