Overview

When scanning a range of computers on the network, GFI LanGuard does not perform a scan on all the machines specified in the network range. Some computers are missing from the Scan Results.

This article provides recommendations on how to properly set up your machines for scanning. 

Information

Environment

GFI LanGuard

Process

Below are the recommendations you can perform to address the issue.

Offline Computers 

By default, GFI LanGuard ignores all machines on a network which do not respond to several ICMP or NetBios requests. This means that the device is either switched off at the time of scanning or that the machine itself or the environment prevents the requests from being processed correctly.

1. Make sure all computers you wish to scan are powered on at the time the scan is performed.
2. Ensure that the appropriate scanner options in the Scanning Profile's Network Discovery properties are enabled:
   1. Open the GFI LanGuard console.
   2. Click Configuration.
   3. Expand Scanning Profiles and choose the appropriate profile.
   4. Go to Edit this Profile > Scanner Options.
      Ensure that only the required Network Discovery methods are enabled.
      For example, if the computer is not responsive to ICMP packets or ping, disable the Ping Sweep option.
3. Increase the Network Discovery Query Response Timeout:
   1. Open the GFI LanGuard console.
   2. Click Configuration.
   3. Expand Scanning Profiles and choose the appropriate profile.
   4. Go to Edit this Profile > Scanner Options.
   5. Under the Network Discovery Options section, increase the Network Discovery Query Responses Timeout value. The default is 500ms.

Licensing 

• When scanning a range of computers, it is essential that GFI LanGuard has sufficient licenses available to save all Scan Results in the database. If the scan has more computers than licenses available, GFI LanGuard will stop scanning as soon as all licenses are consumed.
• The current license status can be checked in the GFI LanGuard Console > General > Licensing
• NOTE: If the database already contains a previous Scan Result for a particular computer, an additional license is not required anymore for that computer during future scans.

IP Range Count

When providing GFI LanGuard with a text file containing IP address ranges to be scanned, GFI LanGuard interprets the ranges in the following manner:

IP address range: 172.16.2.1 - 172.16.3.50

GFI LanGuard interprets this as the next two ranges:

• 172.16.2.1-172.16.2.50
• 172.16.3.1-172.16.3.50

GFI LanGuard does not interpret this as the following two ranges:

• 172.16.2.1-172.16.2.254
• 172.16.3.1-172.16.3.50

NOTE: All machines outside the address range above are not scanned by GFI LanGuard.

Confirmation

Once all recommendations have been performed, GFI LanGuard should be able to scan all target machines specified in the network.

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