Parameters Config
CIST Priority:
Specify the CIST priority of the switch. The valid values are from 0 to
61440, which are divisible by 4096.By default, it is 32768. The switch
with the lower value has the higher priority.
CIST priority is usually a parameter configured in MSTP, which
means the priority of a switch in CIST. The switch with the highest
priority will be elected as the root bridge in CIST.
In STP/RSTP, CIST priority means the priority of a switch in the
spanning tree. The switch with the highest priority is elected as the
root bridge.
Hello Time
Hello Time is 2 seconds, it’s the interval to send BPDUs.
Max Age:
Specify the maximum time the switch can wait without receiving a
BPDU before attempting to regenerate a spanning tree. The valid
values are from 6 to 40 in seconds, and the default value is 20.
Forward Delay:
Specify the time for the port to transit its state after the network
topology is changed. The valid values are from 4 to 30 in seconds,
and the default value is 15.
TxHoldCount:
Specify the maximum BPDU transmission rate of a port. The valid
values are from 1 to 20, and the default value is 5.
Max Hops:
Specify the maximum number of hops that occur in a specific region
before the BPDU is discarded. The valid values are from 1 to 40, and
the default value is 20.
Max Hops is a parameter configured in MSTP. You need not
configure it if the spanning tree mode is STP/RSTP.
Note:
1.
To prevent frequent network flapping, make sure that Hello Time, Forward Delay, and Max
Age conform to the formulas: 2*(Hello Time + 1) <= Max Age, 2*(Forward Delay - 1) >= Max
Age.
2.
The forward delay parameter and the network diameter are correlated. A too small forward
delay parameter may result in temporary loops. A too large forward delay may cause a
network unable to resume the normal state in time. The default value is recommended.
3.
A too small max age parameter may result in the switches regenerating spanning trees
frequently and cause network congestions to be falsely regarded as link problems. A too
large max age parameter result in the switches unable to find the link problems in time,
which in turn handicaps spanning trees being regenerated in time and makes the network
less adaptive. The default value is recommended.
4.
If the TxHold Count parameter is too large, the number of MSTP packets being sent in each
hello time may be increased with occupying too much network resources. The default
value is recommended.
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