Allowed Nodes determines which individual nodes and Monitoring Groups the security row has access to.
If a Monitoring Group is selected, all nodes that are part of the Monitoring Group will be allowed.
Monitoring Groups are much more convenient, and saves you from clicking on many individual nodes.
Nodes also have a Node Mask (designed for those customers of ours who have in excess of 12,000 servers and devices).
The mask works just like the Users and Groups masks, and the Add button and Included sections also work in the same manner.
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