You can have multiple "Preferred APs"in the list. They will be prioritized in the same order that they are provisioned. For example, considering your case.
SM has AP1 as first "Preferred AP"in the list, and AP2 as the second "Preferred AP"in the list.
Case 1: If AP1 is active and AP2 is not active, SM associates with AP1.
Case 2: If both AP1 and AP2 are active and the SM detects them both during the scanning procedure, SM will associate with AP1, as it is provisioned first in the "Preferred AP" list.
Case 3: If AP1 is not active and AP2 is active, SM will associate with AP2.
Notice that currently, in Case 3 above, there is no procedure in the software for the SM to identify if AP1 is back active. So even if AP1 is back in active state, SM will remain associated with AP2 until the next time the SM goes into scanning mode (for example, due to a forced deregistration or a unexpected link disconnect).
Suppose we have a network of 100 towers each with 4 AP (we're WISP). So we have a total of 400 APs Suppose now that the SM is hooked on the AP1 using the PreferredAP.
After 6 months the SM is removed (because the client has ended the relationship with our company) The SM must be installed in another geographic point and needs to connect to the AP #350
It will never connect? Right? And I would not give access to the SM at the installer (for safety reasons), but he access only by my Web centralized Platform, that query the SM for signal, AP, distance and all he need to install it well.
PreferredAP is useful but I need that associate in case of failure of the preferred AP.
Correct. If you have defined a list of Preferred APs in the SM, the SM will look to connect to only the APs in the list. It won't connect to any other APs, even if the SM can see the APs during the scanning procedure.
Is possible to implement a "checkBox" that if selected, SM can connect on AP that are not present in PreferredAP.
In Mikrotik this is the "Default Authentication" check box
So the behaviuor should be:
1 - try before to connect to thePreferredAPs (like now)
2 - if none of these islinkable, try to connect other AP using the only default criteria (Like WPA password) and this only if "Default Authenticate" is checked