6.6.3.3 Setting RSTP Timers
Context
The following timers are used in spanning tree calculation:
l Forward Delay: specifies the delay before a state transition. After the topology of a ring
network changes, it takes some time to spread the new configuration BPDU throughout the
entire network. As a result, the original blocked port may be unblocked before a new port
is blocked. When this occurs, a loop exists on the network. You can set the Forward Delay
timer to prevent loops. When the topology changes, all ports will be temporarily blocked
during the Forward Delay.
l Hello Time: specifies the interval at which hello packets are sent. A switching device sends
configuration BPDUs at the specified interval to detect link failures. If the switching device
does not receive any BPDUs within an interval of Hello Time, the switching device
recalculates the spanning tree.
l Max Age: determines whether BPDUs expire. A switching device determines that a
received configuration BPDU times out when the Max Age expires.
Devices on a ring network must use the same values of Forward Delay, Hello Time, and Max
Age.
You are not advised to directly change the preceding three timers. The three parameters are
relevant to the network scale; therefore, it is recommended that you set the network diameter so
that the spanning tree protocol automatically adjusts these timers. When the default network
diameter is used, the three timers also retain their default values.
NOTICE
To prevent frequent network flapping, make sure that the Hello Time, Forward Delay, and Max
Age timer values conform to the following formulas:
l 2 x (Forward Delay - 1.0 second) >= Max Age
l Max Age >= 2 x (Hello Time + 1.0 second)
Procedure
Step 1 Run:
system-view
The system view is displayed.
Step 2 Set the Forward Delay, Hello Time, and Max Age timers.
1. Run:
stp timer forward-delay forward-delay
The Forward Delay timer is set for the switching device.
By default, the Forward Delay timer is 1500 centiseconds.
2. Run:
stp timer hello hello-time
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
6 STP/RSTP Configuration
Issue 01 (2014-11-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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