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Configuration Guide - Ethernet Switching

S1720, S2700, S5700, and S6720 V200R012(C00 and C20)

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, and Layer 2 protocol transparent transmission.
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Configuring STP Timers

Configuring STP Timers


There are three timers used in spanning tree calculation: Forward Delay, Hello Time, and Max Age. These timers can be configured to affect STP convergence. However, you are not advised to directly change these timers. Instead, it is recommended that you set the network diameter so that the spanning tree protocol automatically adjusts these timers in accordance with the network scale.

The following describes the timers 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 an interval of Hello Time, the device recalculates the spanning tree.
  • Max Age: determines whether a BPDU has timed out. A 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.

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. 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 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 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 device.

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

Updated: 2018-12-24

Document ID: EDOC1100038339

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