Configuring The Timeout Factor - HP A5830 Configuration Manual

Configure the timers on the root bridge only, and the timer settings on the root bridge apply to all devices
on the entire switched network.
To configure the spanning tree timers:
Step...
1. Enter system view
2. Configure the forward delay
timer (in STP/RSTP/MSTP
mode)
3. Configure the forward delay
timer (in PVST mode)
4. Configure the hello timer (in
STP/RSTP/MSTP mode)
5. Configure the hello timer (in
PVST mode)
6. Configure the max age timer
(in STP/RSTP/MSTP mode)
7. Configure the max age timer
(in PVST mode)
The length of the forward delay timer is related to the network diameter of the switched network. The
larger the network diameter is, the longer the forward delay time should be. If the forward delay timer is
too short, temporary redundant paths can occur. If the forward delay timer is too long, network
convergence can take a long time. HP recommends you use the default setting.
An appropriate hello time setting enables the device to quickly detect link failures on the network without
using excessive network resources. If the hello time is too long, the device will mistake packet loss as a
link failure and trigger a new spanning tree calculation process. If the hello time is too short, the device
will frequently send the same configuration BPDUs, which adds the device burden and wastes network
resources. HP recommends you use the default setting.
If the max age timer is too short, the device will frequently begin spanning tree calculation and can
mistake network congestion as a link failure. If the max age timer is too long, the device can fail to
quickly detect link failures and begin spanning tree calculations, reducing the auto-sensing capability of
the network. HP recommends 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 determine 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 fails 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 network resources. In a
stable network, prevent undesired spanning tree calculations by setting the timeout factor to 5, 6, or 7.
Command...
system-view
stp timer forward-delay time
stp vlan vlan-list timer forward-delay
time
stp timer hello time
stp vlan vlan-list timer hello time
stp timer max-age time
stp vlan vlan-list timer max-age time
68
Remarks
—
Optional
Use either command
1500 centiseconds by
default
Optional
Use either command
200 centiseconds by default
Optional
Use either command
2000 centiseconds by
default