Hello,
i Install The Dude (very difficult because missing the information in documentation that work well ONLY if connect to a Read Only account on routers, not with Admin account, no problem) and select to connect to computers on the network (bi-directional firewall full access between Dude and Servers).
The Dude it is capable to connect to SNMP to 20 servers but failed SNMP to 2 servers.
I triple check the SNMP settings and firewall rules and it simply does not want to access SNMP on this 2 machines.
I install another software on neighbor IP and scan al servers and it is working very well on SNMP on ALL servers.
I exhausted my idea of investigation this.
the servers I was talking about is Windows, Firewall is Setup correctly allowing access from Dude IP, SNMP service is setup correctly, identical like others 20 servers.
In Firewall it was created a rule placed Very First on Top allowing Dude Problems Servers.
nothing bring results.
Same time other SNMP Monitoring Software have no problem to connect to ALL Servers, including the two not readable by Dude.
Quite crazy situation.
it will seem strange to you, but if all work but two not:
- delete the servers in the dude and recreate them
or - it depends on the servers (or for something between RouterBOARD and the servers) for some reason not related to RouterOS
Thank you for your advice !
I done this but SNMP not working.
I also install a new DUDE server in the same SUBNET with the Servers who does not work .. and the same ! I check again the settings on this 2 servers and are identical with other servers who work: SNMP Access List basically.
Other Software are able to access via SNMP ALL servers, but Dude only 95 % of the servers, 2 of them are not readable by DUDE 
really crazy.
any more suggestions ?
From RouterOS point of view… none…
1.Try to downgrade the SNMP version to v1 for these two servers.
2.Try using another device with ROS as the agent dude.
3. Try creating a new dude base and add only these two servers to it.
Or give more details.
Have you checked the firewall on the servers?
Can you just for the sake of testing temporarily disable any firewalls in the path?
from 2 servers it remain only 1 because 1 of them it was need to be reinstalled meantime.
Interesting that reinstalling it fix the issue.
this server who remain it is TIME server and it is very delicate to be reinstalled, so not jumping to reinstall a DC and TIME server same time.
I stop firewall. I create another DUDE server on the same SUBNET ! It simply does not want that DUDE to read his SNMP.
In server on SNMP service I setup access from the DUDE IP specially !
I’m study now to see if there is any way to REINITIALIZE Firewall from scratch on server.