Subnet Scanning

The Subnet Scanner

Automatic subnet scanning is one of the methods by which OmniCenter can discover devices in your network. By providing the IP address of a seed device (typically a core router), OmniCenter learns the various subnets within your network that this device is connected to and then scans those subnets for other devices. Any additional subnets connected to those devices are then also scanned for devices, and so on, until OmniCenter learns your entire network. All detected devices are automatically added to OmniCenter for monitoring.

OmniCenter’s subnet scanner will always learn and catalog any subnets it discovers. However, automatic scanning for devices on those subnets can be switched on/off (on by default) both globally and for individual subnets.

When attempting to add a discovered device, OmniCenter tries to authenticate with the device using all authentication credentials added to any of your device templates until it finds a set of credentials that works. So be sure that you have configured correct sets of credentials in at least one device template. (Since device templates do not need to be assigned to any devices for OmniCenter to use their configured credentials, a good practice would be to configure a separate, complete set of device templates that contain only the authentication credentials OmniCenter may need.)

Remember to provide the read-only SNMP community string used for your devices, as well as any usernames and passwords to use for Windows servers (if applicable).

Autodiscovery Scheduling

The subnet scanner is run according to a schedule, which is set on the Auto Discover Schedule administration page (Administration → Add Device → Autodiscovery). By default, the subnet scanner is set to run 24 hours per day, 7 days a week. However, this can be changed to any schedule that works best for your network.

The Auto Discover Schedule administration page.

Auto Discover Schedule Panel

Here, you can create and edit the schedule that controls when OmniCenter scans for new devices. Along the top of the page is displayed the current schedule. This schedule repeats every week. To edit the schedule, click the edit icon in the top right corner of the Autodiscover Schedule panel. The time frames for scheduled autodiscover scans are configured based on the 24-hour clock and must be entered in the following format: 00:00-00:00 (numbers only, separated by colons and dashes, with no spaces), and cannot span multiple days. That is, an autodiscover schedule must begin and end within the 24-hour period of a single day. Like time frames, you may create multiple schedules within the same day, if desired. Simply include a carriage return to enter additional time frames.

Subnet Scanner Settings Panel

Below the schedule are the subnet scanner settings.

  • ENABLE SUBNET SCANNING
    This setting allows you to turn subnet scanning on or off globally, regardless of the schedule (if this setting is switched off the following settings will be hidden).
  • ENABLE AUTO SCANNING OF NEWLY DISCOVERED SUBNETS
    (This setting will be hidden if subnet scanning is switched off.) This setting allows you to prevent newly discovered subnets from being scanned while continuing to scan the subnets that were already known before this setting was switched to off. Be aware that once you return this switch to the ON position, all subnets will be scanned. However, fine control of which subnets are scanned is available in the Subnets panel below these settings.
  • MINIMUM CIDR PREFIX
    (This setting will be hidden if subnet scanning is switched off.) This setting allows you to specify the largest size subnet that OmniCenter will automatically scan for new devices. Discovered subnets that are larger than the size specified by the prefix value will not scan for devices automatically. However, these subnets will still appear in the subnet list and can have automatic scanning activated, if desired. (To understand this setting it’s helpful to remember that the smaller the CIDR prefix, the larger the subnet size. Thus, the minimum CIDR prefix value specifies the largest size subnet that will be scanned automatically.)

Subnets Panel

In the last panel is the list of subnets that OmniCenter currently knows about. Scanning for these subnets can be turned on/off by selecting the subnet(s) using the checkmarks on the left and clicking either the Enable Selected Subnets or Disable Selected Subnets buttons. A subnet’s address can be directly edited by clicking its edit icon in the ACTIONS column. Turning scanning on and off for a single subnet can also be done from within the edit dialog.

Note

Scanning a large range of network addresses can take a long time and generate significant network traffic. We recommend selecting times for your autodiscovery schedule when network traffic will be relatively low.

The Device Discovery Wizard

If it becomes necessary, the device discovery wizard (first run during OmniCenter installation) can be manually run by clicking the Device Discovery Wizard button at the top of the Auto Discover Schedule page or by clicking the edit icon in the Auto Discover Schedule panel and then clicking the Device Discovery Wizard button at the top of the pop-up dialog.

Updated on July 15, 2019

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