User`s manual

EDS-P510 Series Featured Functions
3-40
Max. Age (sec.)
Setting Description Factory Default
Numerical value input
by user
If this device is not the root, and it has not received a hello
message from the root in an amount of time equal to “Max.
Age,” then this device will reconfigure itself as a root. Once two
or more devices on the network are recognized as a root, the
devices will renegotiate to set up a new Spanning Tree
topology.
20
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
Indicates the current Spanning Tree status of this port. “Forwarding” for normal transmission, or “Blocking” to
block transmission.
Configuration Limits of RSTP/STP
The Spanning Tree Algorithm places limits on three of the configuration items described previously:
[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 EDS-P510’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 many ways. One solution is simply to increase the Forwarding Delay value to
at least 11 sec.
HINT: Perform the following steps to avoid guessing:
Step 1: Assign a value to “Hello Time” and then calculate the left most part of Eq. 4 to get the lower limit of
“Max. Age.”