H3C Technologies H3C S10500 Series Switches - Manual (Page 93)

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• Max age
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 a port receives a
configuration BPDU that has expired, that MSTI must be re-calculated. The max age timer is ineffective for
MSTIs.
To avoid frequent network changes, be sure that the settings of the hello time, forward delay and max
age timers 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 devices
on the entire switched network.
Follow these steps to configure the spanning tree timers:
To do... Use the command... Remarks
Enter system view system-view —
Configure the forward delay timer
(in STP/RSTP/MSTP mode)
stp timer forward-delay time
Configure the forward delay timer
(in PVST mode) stp vlan vlan-list timer forward-delay
time
Optional
Use either command.
1500 centiseconds by
default.
Configure the hello timer (in
STP/RSTP/MSTP mode)
stp timer hello time
Configure the hello timer (in PVST
mode)
stp vlan vlan-list timer hello time
Optional
Use either command.
200 centiseconds by default.
Configure the max age timer (in
STP/RSTP/MSTP mode)
stp timer max-age time
Configure the max age timer (in
PVST mode)
stp vlan vlan-list timer max-age time
Optional
Use either command.
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 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 quickly 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 adds the device burden and wastes network
resources. H3C recommends you to use the default setting.
• If the max age timer is too short, the device will frequently begin spanning tree calculation and might
mistake network congestion as a link failure. If the max age timer is too long, the device might fail to
quickly detect link failures and begin spanning tree calculations, reducing the auto-sensing capability of
the network. H3C recommends you to use the default setting.