Configuring The Timeout Factor - HP 5820X series Configuration Manual

To configure the timers of MSTP:
To do...
1. Enter system view
2. Configure the forward delay
timer
3. Configure the hello timer
4. Configure the max age timer
The length of the forward delay is related to the network diameter of the switched network. The larger the
network diameter is, the longer the forward delay should be. If the forward delay is too short, temporary
redundant paths can be introduced. If the forward delay is too long, it may take a long time for the
network to converge. HP recommends that you use the default setting.
An appropriate hello time enables the device to timely detect link failures on the network without using
excessive network resources. If the hello time is set too long, the device will take packet loss as a link
failure and trigger a new spanning tree calculation process. If the hello time is set too short, the device
will send repeated configuration BPDUs frequently, which adds to the device burden and causes waste of
network resources. HP recommends that you use the default setting.
If the max age time is too short, the network devices will frequently launch spanning tree calculations and
may take network congestion as a link failure. If the max age is too long, the network may fail to timely
detect link failures and fail to timely launch spanning tree calculations, reducing the auto-sensing
capability of the network. HP recommends that you use the default setting.

Configuring the timeout factor

The timeout factor is a parameter used to decide the timeout time in the following formula: Timeout time =
timeout factor × 3 × hello time.
After the network topology is stabilized, each non-root-bridge device forwards configuration BPDUs to the
downstream devices at the interval of hello time to check whether any link is faulty. If a device does not
receive a BPDU from the upstream device within nine times the hello time, it assumes that the upstream
device has failed and starts a new spanning tree calculation process.
Sometimes a device may fail to receive a BPDU from the upstream device because the upstream device is
busy. If a spanning tree calculation occurs, the calculation can fail and also waste the network resources.
In a very stable network, you can avoid such unwanted spanning tree calculations by setting the timeout
factor to 5, 6, or 7.
To configure the timeout factor:
To do...
1. Enter system view
2. Configure the timeout factor of the device
Use the command...
system-view
stp timer forward-delay time
stp timer hello time
stp timer max-age time
Use the command...
system-view
stp timer-factor factor
76
Remarks
—
Optional
1500 centiseconds (15 seconds)
by default
Optional
200 centiseconds (2 seconds) by
default
Optional
2000 centiseconds (20 seconds)
by default
Remarks
—
Required
3 by default