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3Com Switch 7750 Series
Command Reference Guide – MSTP Chapter 1
MSTP Configuration Commands
1-43
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
prevent network jitter.
2 x (Forward delay – 1 second) >= Max age
Max age >= 2 x (Hello time + 1 second)
You are recommended to specify the network diameter of the switched network and the
Hello 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-view
System View: return to User View with Ctrl+Z.
[3Com] stp timer forward-delay 2000
1.1.41 stp timer hello
Syntax
stp timer hello centi-seconds
undo stp timer hello
View
System view
Parameter
centi-seconds: Hello time in centiseconds to be set. This argument ranges from 100 to
1,000 and defaults to 200.
Description
Use 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 existing
spanning trees. The Hello time is used to set the sending interval. When a switch
becomes a root bridge, it regularly sends BPDUs at the interval specified by the hello
time you have configured on it. While, the other none-root-bridge switches listen to the
BPDUs; if they do not receive a BPDU in a specific period, spanning trees will be
regenerated.