When you decide to run Discovery and EM1 periodically, pay attention to the following:
To adjust the Discovery and EM1 settings:
If you have defined (additional) IP ranges and you want these ranges also being scanned periodically, check the Run discovery checkbox and define a time interval. The default scanning interval is 9 hours. Additional IP ranges are also scanned by EM1 if EM1 is enabled.
Note that if you want to make a one-time-only scan of one or more IP ranges in order to use the discovered nodes for building a new network map, leave the Run Discovery every checkbox unchecked! Go instead to the "Discovery / Discover IP nodes" window directly, define one or more ranges and run Discovery interactively.
We would like to remind you - perhaps unnecessarily – that if you leave the Run Discovery every checkbox unchecked and the Enable EM1 checkbox checked, EM1 will automatically scan the devices on the map every four hours. The time interval specified in the Discovery pane is not used by EM1!
If Discovery finds a new IP node, it tries to retrieve SNMP data from the node using the communities listed in the Communities to use listbox. The first six community strings in the list are system defaults that cannot be removed or modified.
Adding new communities to the list
Removing communities from the list
Defining EM1 Thresholds
Modifying EM1 thresholds is not recommended! The default settings have been determined by extensive testing.
Note that, if Discovery is running, some intrusion detection systems may start sending alerts in order to inform the network manager that someone is trying to connect to an abnormally high number of hosts with an abnormally high number of different community names, which may indicate that a network attack is under course.