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Configuration Guide - Ethernet Switching

S7700 and S9700 V200R011C10

This document describes the configuration of Ethernet services, including configuring link aggregation, VLANs, Voice VLAN, VLAN mapping, QinQ, GVRP, MAC table, STP/RSTP/MSTP, SEP, and so on.
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Setting the Values of MSTP Timers

Setting the Values of MSTP Timers


The following timers are used in spanning tree calculation:
  • 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.
  • Hello Time: specifies the interval at which hello packets are sent. A device sends configuration BPDUs at the specified interval to detect link failures. If the switching device does not receive any BPDUs within the timeout period (timeout period = Hello Time x 3 x Timer Factor), the device recalculates the spanning tree.
  • 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.

To prevent frequent network flapping, make sure that the Hello Time, Forward Delay, and Max Age timer values conform to the following formulas:

  • 2 x (Forward Delay - 1.0 second) ≥ Max Age

  • Max Age ≥ 2 x (Hello Time + 1.0 second)


  1. Run system-view

    The system view is displayed.

  2. (Optional) Run stp process process-id

    The MSTP process view is displayed.


    Skip this step if you perform configurations in the MSTP process 0.

  3. Set Forward Delay, Hello Time, and Max Age.
    1. Run stp timer forward-delay forward-delay

      The value of Forward Delay of the switch is set.

      By default, the value of Forward Delay of the switch is 1500 centiseconds.

    2. Run stp timer hello hello-time

      The value of Hello Time of the switch is set.

      By default, the value of Hello Time of the switch is 200 centiseconds.

    3. Run stp timer max-age max-age

      The value of Max Age of the switch is set.

      By default, the value of Max Age of the switch is 2000 centiseconds.

Updated: 2019-10-18

Document ID: EDOC1000178310

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