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S12700 V200R010C00 Configuration Guide - Ethernet Switching

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 STP Timers

Setting STP Timers

Context

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. This creates a loop 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 when 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 for Forward Delay, Hello Time, and Max Age.

You are not advised to directly change the preceding three parameters as they are related 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 use 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 second) >= Max Age

  • Max Age >= 2 x (Hello Time + 1 second)

Procedure

  1. Run:

    system-view

    The system view is displayed.

  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 (15 seconds).

    2. Run:

      stp timer hello hello-time

      The Hello Time is set for the switching device.

      By default, the Hello Time is 200 centiseconds (2 seconds).

    3. Run:

      stp timer max-age max-age

      The Max Age timer is set for the switching device.

      By default, the Max Age timer is 2000 centiseconds (20 seconds).

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Updated: 2019-08-21

Document ID: EDOC1000142081

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