Configuration Restrictions And Guidelines; Configuration Procedure - HPE FlexFabric 5940 Series Configuration Manual

its state after a forward delay timer. This ensures that the state transition of the local port stays
synchronized with the peer.
•
Hello time—Interval at which the device sends configuration BPDUs to detect link failures. If
the device does not receive configuration BPDUs within the timeout period, it recalculates the
spanning tree. The formula for calculating the timeout period is timeout period = timeout factor ×
3 × hello time.
•
Max age—In the CIST of an MSTP network, the device uses the max age timer to determine
whether a configuration BPDU received by a port has expired. If it is expired, a new spanning
tree calculation process starts. The max age timer does not take effect on MSTIs.
To ensure a fast topology convergence, make sure the timer settings meet the following formulas:
•
2 × (forward delay – 1 second) ≥ max age
•
Max age ≥ 2 × (hello time + 1 second)
As a best practice, specify the network diameter and letting spanning tree protocols automatically
calculate the timers based on the network diameter instead of manually setting the spanning tree
timers. If the network diameter uses the default value, the timers also use their default values.
Set the timers only on the root bridge. The timer settings on the root bridge apply to all devices on the
entire switched network.

Configuration restrictions and guidelines

When you set spanning tree timers, follow these restrictions and guidelines:
•
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 time should be. As a best practice,
use the automatically calculated value because inappropriate forward delay setting might cause
temporary redundant paths or increase the network convergence time.
•
An appropriate hello time setting enables the device to promptly detect link failures on the
network without using excessive network resources. If the hello time is too long, the device
mistakes packet loss for a link failure and triggers a new spanning tree calculation process. If
the hello time is too short, the device frequently sends the same configuration BPDUs, which
wastes device and network resources. As a best practice, use the automatically calculated
value.
•
If the max age timer is too short, the device frequently begins spanning tree calculations and
might mistake network congestion as a link failure. If the max age timer is too long, the device
might fail to promptly detect link failures and quickly launch spanning tree calculations, reducing
the auto-sensing capability of the network. As a best practice, use the automatically calculated
value.

Configuration procedure

To set the spanning tree timers:
Step
Enter system view.
1.
Set the forward delay
2.
timer.
Command
system-view
•
In STP/RSTP/MSTP mode:
stp timer forward-delay time
•
In PVST mode:
stp vlan vlan-id-list timer
forward-delay time
110
Remarks
N/A
The default setting is 15 seconds.