User tags are derived from ordinary SNMP variables, in most cases, implementing special calculations to obtain performance indicators based on raw SNMP data.

User Tags List

There are three columns in the tag list view:

Enable: Indicates if the tag is active to server scan.

tag Name: Name that will be used by the server to publish this variable.

tag Description: An explain text for the tag.

To manually add a User tag, you can use the Add tag button on the top toolbar. Alternatively, you can right-click any empty space in tag View and select Add tag from the context menu.

Tag Properties Toolbar

You can edit properties of a particular tag by either selecting it on the list and clicking on the tag Properties button on the top toolbar or right-clicking the tagand choosing tag Properties from the context menu.

Both options (adding or editing a User tag item) will display a detailed tag configuration dialog box.

The User Tag Properties Dialog

You can customize the following item settings:
 

tag Name: The name of the tag.

Description: A textual description of the displayed value of the tag.

Expression: The expression used to calculate this tag. You can edit this field clicking on Edit Expression button.

1st Order Filter: Check to create an additional tag (with "_Filtered" in the name) that applies a low pass filter in this item. This is only available for numerical variables.

To edit the Expression, click on Edit Expression button.

The Expression Wizard will open. In the first step, define the expression using variables, in example you see the utilization formula:

utilization = ( ( 8 * ( delta(a) + delta(b) ) ) * c ) * 100

You can use up to eight variables to construct your own expression. Note that latin characters are not allowed to variable names.

It is possible to use the four basic operations - addition( + ), subtraction( - ), multiplication( * ) and division( / ) - and the delta function. This function calculate the delta of the specified variable:

delta(x) - calculate the difference between the current x value and the last saved value.

You can group expression parts using parentheses, simplifying the human reading and changing the formula interpretation: a + b / c is different from (a + b) / c.

During expression edit, a validator will be executed below the expression box. If "The expression is invalid" text is show, an error was found and the formula needs to be revised.

Then, in step two, define the SNMP OID for each variable. Note that each variable is associated with a SNMP OID, so if device MIB Tree changes, all User tags must be checked for changes too.

You can search for a tag in tag List in the right of the dialog. This list is loaded from RAW tags List, so it's recommended that you scan the device for MIB-II OIDs before creating/editing User tags.
 

To simplify the search task, you can use the Look for filter at top of the tag List. Type a match expression for SNMP MIB column and all tags will be filtered. Then drag-and- drop the selected tag to the specified variable.

Calculation Expression Wizard

To change the SNMP OID of a variable, drag a new OID to it.

To finish this Wizard and save the new expression, click on the Finish button.

Notice that you must enable and configure your SNMP device before setting up traps in the server.

After editing or adding the tag, click on the OK button to close the User tag Properties dialog and update the item settings. If you want to discard all changes, just click the Cancel button to close the dialog.