H3C Technologies H3C S3100 Series Switches - Manual (Page 193)

Operation Manual – MSTP
H3C S3100-52P Ethernet Switch
Chapter 1 MSTP Configuration
1-18
Caution:
z
The forward delay parameter and the network diameter are correlated. Normally, a
large network diameter corresponds to a large forward delay. A too small forward
delay parameter may result in temporary redundant paths. And a too large forward
delay parameter may cause a network unable to resume the normal state in time
after changes occurred to the network. The default value is recommended.
z
An adequate hello time parameter enables a switch to detect link failures in time
without occupying too many network resources. And a too small hello time
parameter may result in duplicated configuration BPDUs being sent frequently,
which increases the work load of the switches and wastes network resources. The
default value is recommended.
z
As for the max age parameter, if it is too small, network congestion may be falsely
regarded as link failures, which results in frequent spanning tree recalculation. If it is
too large, link problems may be unable to be detected in time, which prevents
spanning trees being recalculated in time and makes the network less adaptive. The
default 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 prevent
frequent 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 determined automatically.
II. Configuration example
# Configure the forward delay parameter to be 1,600 centiseconds, the hello time
parameter to be 300 centiseconds, and the max age parameter to be 2,100
centiseconds (assuming that the current switch operates as the CIST root bridge).
system-view
[H3C] stp timer forward-delay 1600
[H3C] stp timer hello 300
[H3C] stp timer max-age 2100
1.2.10 Configuring the Timeout Time Factor
A switch regularly sends protocol packets to its neighboring devices at the interval
specified by the hello time parameter to test the link failures. Normally, a switch regards