19             Discovery of Network Elements (Pro Edition)

With MIB Explorer, SNMPv1/v2c/v3 command responder, generators and other network elements can be discovered in a Local Area Network (LAN) by using broadcast targets and other targets (e.g. routers or bridges) as seeds. To perform a discovery you need to specify at least one seed target. That target should use a community or SNMPv3 user common to most (possible) targets in your network.

Besides active discovery, source addresses of notifications are also covered by the discovery process.

To Discover Network Elements

1.   Choose the Discovery tab from the Tools panel.

2.   If you have not yet defined targets to be used as seeds, choose Discov­ery Preferences () from the toolbar. A configuration dialog with three tabs will be opened:

• In the first tab you specify the seed targets, by adding them to to right list of the shuffle lists.

• The refresh interval and the scan interval in seconds are specified in the second tab. The refresh interval defines the number of seconds MIB Explorer will wait until it refreshes the state of each discovered network element. The scan interval must be less or equal to the refresh interval. The scan interval defines the number of seconds MIB Explorer will scanning for new network elements and updating exist­ing ones.

• With the third tab additional variables may be defined that should be collected by the discovery process. The given OIDs will be added to the GET request sent to discovered network elements. The default variables requested are:  

ifNumber.0, sysName.0, sysUpTime.0, sysLocation.0, sysContact.0, sysDescr.0, sysObjectID.0, and sysSer­vices.0

19.1            Toolbar

Figure 16:                             Discovery toolbar.

• Start

Starts the discovery process. All items in the discovery table will be removed and newly discovered network elements will be added to the table in background.

• Stop

Stops the discovery process. This may take a few seconds.

• Refresh

Discovers agents using the selected target and add them to the result table. Already discovered targets will be updated. A GET PDU is send to the IP address and UDP port specified in the discovery target. The PDU's variable bindings are. If a target responds with an error status other than 0 (no error), the target will not be displayed in the result table. Instead, the error counter will be incremented by one and dis­played in the Status Bar.

•  Add Selected Network Elements to Target Configuration

Adds the selected targets to MIB Explorer's configuration. Each target will be named by its discovered system name (sysName.0). The selected targets will be contacted with the configured seed target secu­rity information (by order of their position in the seed configuration list). The new target gets the configuration of the first seed whose security information results in a successful contact.

• Discovery Preferences

Opens the target configuration window, where you can make adjust­ments to any target, in particular discovery targets. The target selected in the configuration when you save your changes using the Save but­ton will become the next discovery target.

19.2            Table of Discovered Network Elements

The table of discovered network elements may contain SNMP command responder (typically agents) as well as simple network addresses discovered from notifications and routers. If a network element has been discovered through evaluation of a system's address table then that source system's IP address will be displayed in the Source Address column.

The Last Contact column shows the the time of the last update of the discovered variables of the network element. If there is not any time shown, then no variables has been discovered for the network element and it could not be contacted with a ping. The refresh interval for the variables can be configured with the Discovery Preferences.