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EDS-408A/405A Series User’s Manual Featured Functions
3-28
Enable STP per Port
Setting Description Factory Default
Enable/Disable
Select to enable the port as a node
on the Spanning Tree topology.
Disabled
NOTE
We suggest not enabling the Spanning Tree Protocol once the port is connected to a device (PLC,
RTU, etc.) as opposed to network equipment. The reason is that it will cause unnecessary
negotiation.
Port Priority
Setting Description Factory Default
Numerical value
selected by user
Increase this port’s priority as a
node on the Spanning Tree
topology by entering a lower
number.
128
Port Cost
Setting Description Factory Default
Numerical value
input by user
Input a higher cost to indicate that
this port is less suitable as a node
for the Spanning Tree topology.
200000
Port Status
This indicates the current Spanning Tree status of this port. The status values are Forwarding for
normal transmission, and Blocking to block transmission.
Configuration Limits of RSTP/STP
The Spanning Tree Algorithm places limits on three of the configuration items previously
described:
[Eq. 1]: 1 sec ≦ Hello Time ≦ 10 sec
[Eq. 2]: 6 sec ≦ Max. Age ≦ 40 sec
[Eq. 3]: 4 sec ≦ Forwarding Delay ≦ 30 sec
These three variables are further restricted by the following two inequalities:
[Eq. 4]: 2 * (Hello Time + 1 sec) ≦ Max. Age ≦ 2 * (Forwarding Delay – 1 sec)
MOXA EtherDevice Switch’s firmware will alert you immediately if any of these restrictions are
violated. For example, setting
Hello Time = 5 sec, Max. Age = 20 sec, and Forwarding Delay = 4 sec does not violate Eqs. 1
through 3, but does violate Eq. 4, since in this case,
2 * (Hello Time + 1 sec) = 12 sec, and 2 * (Forwarding Delay – 1 sec) = 6 sec.
You can remedy the situation in a multitude of ways. One solution is simply to increase the
Forwarding Delay to at least 11 sec.