Subnet Scanner Management

See also, Auto-Discovery

The Subnet Scanner

Automatic subnet scanning is one method by which Netreo can discover devices in your network. By providing the IP address of a seed device (typically a core router), Netreo 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 Netreo learns your entire network. All detected devices are automatically added to Netreo for monitoring.

Netreo'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, Netreo 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 the correct sets of credentials in at least one device template. (Since device templates do not need to be assigned to any devices for Netreo 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 Netreo may need.)

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

Scan Period

It is important to understand that the subnet scanner does not continuously scan for new devices.

The subnet scanner attempts to scan each subnet in your network (one at a time, in sequence) a maximum of once per day in accordance with the restrictions of the auto-discover schedule (below). However, depending on the size of the environment and the number of devices to be monitored, it may take several days to complete a scan of all of the subnets in your network.

So, under optimal conditions, each subnet is scanned once per day. However, in a large network, each subnet may only be scanned once every several days. This means that there could be a considerable delay between the time when a device is added to your network and the time when it is discovered by Netreo.

Autodiscovery Scheduling

Subnet scanning can be resource intensive, so the scanner may be restricted to run only during certain periods (such as non-working hours) using a schedule set on the Auto Discover Schedule administration page (Administration > Add Device > Autodiscovery). By default, the subnet scanner is allowed to run at any time of day, every day of the week. However, this can be changed to best suit your needs.

Auto Discover Schedule Panel

Here, you can edit the schedule that controls when Netreo may scan for new devices. To edit the schedule, click the edit icon in the top right corner of the panel.

Time frames within a schedule are configured based on the 24-hour clock. They include a start and end time and must be entered in the following format: 00:00-00:00 (numbers only, separated by colons and dashes with no spaces).

A time frame may not span multiple days. That is, it must begin and end within the 24-hour period of the day it is scheduled to occur. You can, however, create multiple time frames within the schedule of a single day if desired. Simply include a carriage return after a time frame while editing to enter the next time frame for that day.

Subnet Scanning 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, control over which subnets are scanned is still 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 Netreo 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 Netreo 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.

The address of a subnet may be edited directly by selecting 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.

The Device Discovery Wizard

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