Stp Timer-Factor - 3Com 5500-EI PWR Reference Manual

MSTP is capable of detecting link failures and automatically restoring redundant links to the forwarding
state. In CIST, switches use the max age parameter to judge whether or not a received configuration
BPDU times out. Spanning trees will be recalculated if a configuration BPDU received by a port times
out.
The max age is meaningless to MSTIs. The max age configured for the root bridge of the CIST applies
to all switches operating on the CIST, including the root bridge.
As for the configuration of the three time-related parameters (namely, the hello time, forward delay, and
max age parameters), the following formulas must be met to prevent frequent network jitter:
You are recommended to specify the network diameter of the switched network and the hello time
parameter by using the stp root primary or stp root secondary command. After that, the three proper
time-related parameters are automatically determined by MSTP.
Related commands: stp timer forward-delay, stp timer hello, stp bridge-diameter.
Examples
# Set the max age to 1,000 centiseconds.
<Sysname> system-view
System View: return to User View with Ctrl+Z.
[Sysname] stp timer max-age 1000

stp timer-factor

Syntax
stp timer-factor number
undo stp timer-factor
View
System view
Parameters
number: Hello time factor to be set, in the range of 1 to 10.
Description
Use the stp timer-factor command to set the timeout time of a switch in the form of a multiple of the
hello time.
Use the undo stp timer-factor command to restore the hello time factor to the default value.
By default, the hello time factor of the switch is 3.
A switch regularly sends protocol packets to its neighboring devices at the interval specified by the hello
time parameter to test the links. Generally, a switch regards its upstream switch faulty if the former does
receive any protocol packets from the latter in a period three times of the hello time and then initiates the
spanning tree recalculation process.
Spanning trees may be recalculated even in a steady network if an upstream switch is always busy. You
can configure the hello time factor to a larger number to avoid this problem. Normally, the timeout time
2 × (forward delay – 1 second) >= max age,
Max age >= 2 × (hello time + 1 second).
1-43