H3C Technologies H3C WX5500E Series Access Controllers - Manual (Page 87)

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In the CIST of an MSTP network or each VLAN of a PVST network, the device uses the max age
parameter to determine whether a configuration BPDU received by a port has expired. If it has, a
new spanning tree calculation process starts. The max age timer is ineffective for MSTIs.
To prevent network instability, make sure that your timer settings meet the following formulas:
{
2 × (forward delay – 1 second) ≥ max age
{
Max age ≥ 2 × (hello time + 1 second)
H3C does not recommend manually setting the spanning tree timers. Instead, H3C recommends
that you specify the network diameter and use the automatically calculated timers based on the
network diameter. If the network diameter uses the default value, the timers also use their default
values.
Configure timers on the root bridge only. The timer settings on the root bridge apply to all devices
on the entire switched network.
Configuration restrictions and guidelines
• The length of the forward delay timer is related to the network diameter of the switched network. The
larger the network diameter, the longer the forward delay time should be. If the forward delay timer
is too short, temporary redundant paths might occur. If the forward delay timer is too long, network
convergence might take a long time. H3C recommends you to use the default setting.
• An appropriate hello time setting enables the device to promptly detect link failures on the network
without using excessive network resources. If the hello time is too long, the device will mistake
packet loss as a link failure and trigger a new spanning tree calculation process. If the hello time is
too short, the device will frequently send 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 will frequently launch spanning tree calculation and
may mistake network congestion as a link failure. If the max age timer is too long, the device may
fail to detect link failures and launch spanning tree calculations promptly, reducing the auto-sensing
capability of the network. H3C recommends you to use the default setting.
Configuration procedure
To configure the spanning tree timers:
Step Command Remarks
1. Enter system view. system-view N/A
2. Configure the forward
delay timer.
• In STP/RSTP/MSTP mode:
stp timer forward-delay time
• In PVST mode:
stp vlan vlan-list timer forward-delay
time
Optional.
Use one of the commands.
The default setting is 15
seconds.
3. Configure the hello timer.
• In STP/RSTP/MSTP mode:
stp timer hello time
• In PVST mode:
stp vlan vlan-list timer hello time
Optional.
Use one of the commands.
The default setting is 2
seconds.
4. Configure the max age
timer.
• In STP/RSTP/MSTP mode:
stp timer max-age time
• In PVST mode:
stp vlan vlan-list timer max-age time
Optional.
Use one of the commands.
The default setting is 20
seconds.