You can see an overview of all the environments in your catalog in the Overview tab. To open it, double-click on the root node of your catalog or click Options > Overview.
The overview tab displays a table for each environment where the rows are each one of its servers. In case there were servers that do not belong to any environment, they are displayed in a separated table. As the rest of tables, you can select which measures to monitor in each table and they will automatically refresh its content.
The servers that are unreachable are displayed as blurred rows.