H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 80)

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The device detects whether a link failure has occurred with the hello time interval. The spanning
tree sends out a configuration BPDU every hello time interval. If the device receives no
configuration BPDUs within the hello time interval, it recalculates the spanning tree.
• Max age
In the CIST of an MSTP network, the device determines whether a configuration BPDU received by
a port has expires based on the max age timer. If yes, a new spanning tree calculation process
starts. The max age timer is ineffective for MSTIs.
To prevent network instability, make sure that the timer settings meet the following formulas:
• 2 × (forward delay – 1 second) ƒ max age
• Max age ƒ 2 × (hello time + 1 second)
H3C does not recommend you to manually set the spanning tree timers. Instead, you can specify the
network diameter and let spanning tree protocols automatically calculate the timers based on the
network diameter. If the network diameter uses the default value, the timers also use their default values.
Configure the timers on the root bridge only, and the timer settings on the root bridge apply to all the
devices on the entire switched network.
To configure the spanning tree timers:
Step Command Remarks
1. Enter system view. system-view N/A
2. Configure the forward delay
timer.
stp timer forward-delay time
Optional.
1500 centiseconds by default.
3. Configure the hello timer. stp timer hello time
Optional.
200 centiseconds by default.
4. Configure the max age timer. stp timer max-age time
Optional.
2000 centiseconds by default.
NOTE:
•
The length of the forward delay timer is related to the network diameter of the switched network. The
larger the network diameter is, the longer the forward delay time should be. If the forward delay timer
is too short, temporary redundant paths may be introduced. If the forward delay timer is too long, it may
take a long time for the network to converge. H3C recommends you to use the default setting.
• An appropriate hello time setting enables the device to timely detect link failures on the network without
using excessive network resources. If the hello time is too long, the device considers packet loss as a link
failure and trigger a new spanning tree calculation process. If the hello time is too short, the device
frequently sends the same configuration BPDUs, which add the device burden and waste network
resources. H3C recommends you to use the default setting.
• If the max age timer is too short, the device frequently launches spanning tree calculation and may
consider network congestion as a link failure. If the max age timer is too long, the device may fail to
timely detect link failures and launch spanning tree calculation, reducing the auto-sensing capability of
the network. H3C recommends you to use the default setting.