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Discovery is the way by which OpenNMS finds nodes (devices with a network address). Discovery can be either automatic or manual, depending on your preference. For smaller networks, manual addition of nodes is feasible, but larger networks will benefit significantly from automatic discovery.

Automatic Discovery

Before starting OpenNMS, you configure OpenNMS with the relevant address ranges (typically one or more subnets, but the syntax is flexible). Optionally you can configure your local SNMP community strings, with significant flexibility in using different community strings for different address ranges or specific addresses.

Once configured, start OpenNMS, and your network will be automatically discovered. The Discovery daemon sends out ICMP pings to see if something responds on that IP address. If a response is received, a "New Suspect" event is generated and passed into the OpenNMS event system. The Capabilities daemon picks that event up and scans that IP address for available services that OpenNMS knows about. The node and it's services will be added to the OpenNMS database; monitoring and data collection will commence for that node.

Semi-automatic discovery

If full automatic discovery is not for you, OpenNMS will generate NewSuspect events for any unknown nodes that send the OpenNMS server an SNMP trap. This means that with OpenNMS running, you can configure your SNMP agent on the host to send traps to the public community on the OpenNMS server, restart the SNMP agent (which typically causes a "Cold Start" trap to be sent), and OpenNMS will discover that node and schedule a capabilities scan.

Manual discovery

For some who desire more control, or who only have small network, individual nodes can be manually added. There are two significant ways to add nodes manually:

  1. Via the web-interface, by entering the IP address, or
  2. Using the script to send a New Suspect event

In the second case for example, custom scripts can be written to obtain appropriate IP addresses from existing systems or databases, and feed these into OpenNMS

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