How to Prevent Supernet Creation in ITMS Using the InvalidSubnets Core Setting

Products

• IT Management Suite

Issue/Introduction

In some IT Management Suite (ITMS) environments, administrators observe that unexpected supernets (large subnet ranges such as /8, /14, or /16) appear under Sites and Subnets in the SMP Console.

These supernets may cause:

• Clients downloading packages from incorrect package servers

• Unexpected cross-site traffic

• Performance issues when agents connect to remote infrastructure

• Administrative overhead because deleted supernets reappear after inventory synchronization

Administrators often attempt to remove these entries manually or disable scheduled tasks, but the supernets may still be recreated during subnet synchronization.

Environment

ITMS 8.7.x, 8.8.x

Cause

Supernets appear due to automatic subnet creation mechanisms in ITMS.

The most common sources include:

Source	Behavior
Basic Inventory	Agents report TCP/IP configuration which includes subnet information. The platform may generate subnet resources from this data.
Manual “Re-Synchronize Subnets”	Rebuilds subnet resources based on discovered network data.
Subnet Resource Creation Schedule	Scheduled task that creates subnet resources from inventory data.

When large masks such as /8, /14, or /16 are reported, the system may create overlapping supernets, which can cause site mapping conflicts.

Resolution

ITMS can automatically create subnet resources based on network information reported by agents. When inventory reports include large subnet masks (for example /8 or /16), ITMS may generate supernet entries that overlap with existing site subnet mappings.

To control this behavior, administrators can create (see Updating Core Settings in ITMS 8.5 and later) a Notification Server Core Setting called:

InvalidSubnets

This setting allows administrators to define a Regex filter. Any subnet that matches the pattern is blocked from being created in the SMP Console. This approach prevents undesirable supernets from being generated while still allowing normal subnet discovery.

The recommended solution is to configure the InvalidSubnets Core Setting to filter out undesired subnet masks.

This prevents the creation of large supernets while still allowing normal subnet discovery.

Table of Contents

• Step 1 – Open SMP Core Settings
• Step 2 – Create the InvalidSubnets Setting
• Step 3 – Remove Existing Supernets
• Step 4 – Validate the Configuration
  • Option A – Manual Sync
  • Option B – Direct Delete
  • Important Behavior Notes
  • Verification
  • Troubleshooting

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Step 1 – Open SMP Core Settings

1. Open the SMP Console.

2. Navigate to:

Settings > Notification Server > Core Settings

3. Click + (Add) to create a new core setting.

4. Call it: InvalidSubnets
   
   
    

Step 2 – Create the InvalidSubnets Setting

Configure the following values:

Setting	Value
Name	InvalidSubnets
Type	String
Value	Regex pattern matching subnet masks you want to block

The value must be a Regular Expression (Regex) pattern.

If a subnet matches the pattern, the platform will not create the subnet resource.

Example use case:

Goal	Regex Behavior	Example Value
Prevent supernets smaller than /24	Match subnet masks like /8, /14, /16, etc.	[^\/]+\/([0-9]|1[0-9]|2[0-3])$

Step 3 – Remove Existing Supernets

If supernets already exist:

1. Go to:

Manage > Sites > Subnets

2. Identify supernet entries such as:

   • /8

   • /14

   • /16

3. Delete the unwanted subnet resources.

After the InvalidSubnets setting is active, those entries should not be recreated during subnet synchronization.

Step 4 – Validate the Configuration

Run a subnet synchronization process to verify the filter works.

Option A – Manual Sync

• On the SMP Console, go to 'Settings > Notification Server > Site Server Settings' menu
• Expand 'Subnets' in the left panel
• Push 'Re-Synchronize Subnets' button
  
  
  
  
• Check the "Delete non-managed subnets" check-box



Option B – Direct Delete

• On the SMP Console, go to 'Settings > Notification Server > Site Server Settings' menu
• Expand 'Subnets' in the left panel
• Find all the supernets that you don't want to keep. 
• Select the supernet > right-click > Delete

Expected behavior:

Scenario	Result
Subnet matches InvalidSubnets regex	Subnet is NOT created
Subnet does not match regex	Subnet is created normally

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Important Behavior Notes

Scenario	Result
Basic Inventory generated subnets	Filtered by InvalidSubnets
Manual subnet synchronization	Filtered by InvalidSubnets
Subnet Resource Creation Schedule	Filtered by InvalidSubnets
Active Directory Import	Not filtered (AD subnets will still be created). This occurs because AD Import directly creates subnet resources defined in Active Directory, bypassing this filter.

 

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Verification

To confirm the configuration is working:

1. Run Re-Synchronize Subnets.

2. Check:

Manage > Sites > Subnets

3. Confirm that:

• Large masks such as /8, /14, /16 are not recreated

• Only valid subnet ranges appear.

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Troubleshooting

Symptom	Possible Cause	Action
Supernets still appear	Regex pattern incorrect	Verify regex syntax
Supernets reappear after AD Import	AD subnets bypass filter	Review subnet definitions in Active Directory
Correct subnets not appearing	Regex too restrictive	Adjust pattern to allow required subnet masks

Additional Information

Cleaning up unused subnets from your SMP Server

Subnets are being created from Inventory which causes problems with Site assignment and package download