Discovery is creating duplicate CI entries across multiple MID Servers

[SandeepKSingh]

We have multiple MID Servers across different data centers. During a Discovery run, the same Windows server is being discovered by multiple MID Servers, resulting in duplicate cmdb_ci_computer records in CMDB.
The CMDB health score is dropping, and reconciliation is failing because the same CI has different serial_number or fqdn attributes populated inconsistently.

How do we identify the root cause and fix it so that Discovery stops creating duplicate CIs?

[Ravi Gaurav · Accepted solution]

Hi @SandeepKSingh 

Please follow the below steps :-

Note: Below steps is From Servicenow Product documentaion and my analysis

1. Validate Identification Rules:
   Go to CI Class Manager → cmdb_ci_computer → Identification Rule.
   Check if the rule includes strong identifiers like:

   • Serial Number

   • Fully Qualified Domain Name (FQDN)

   • BIOS UUID
     If only IP address or hostname is used, duplicates are likely because multiple MID Servers may reach the same host with different IPs.

2. Check Discovery Behavior:

   • Open the Discovery logs in the Discovery Status record.

   • Confirm whether Discovery uses multiple IPs from different IP ranges to identify the same host.

   • If yes, consolidate subnets or assign Discovery ranges to specific MID Servers based on IP segmentation or location.

3. Review Identification and Reconciliation (I&R) Rules:

   • Ensure IRE (Identification and Reconciliation Engine) is active and properly configured.

   • If you’re on a newer release (Tokyo+), make sure I&R Definition Rules are not overridden.

   • Prioritize authoritative sources (like Discovery) over imports or integrations in the Reconciliation Definitions.

4. Remediation:

   • Clean up duplicate records using Duplicate CI Remediator or a manual merge rule.

   • Adjust Discovery Schedule to avoid overlapping IP ranges.

   • Modify Identification Rule to use a stronger combination (FQDN + Serial Number).

   • Re-run Discovery and validate no new duplicates appear.

[Ravi Gaurav · Accepted solution]

Hi @SandeepKSingh 

Please follow the below steps :-

Note: Below steps is From Servicenow Product documentaion and my analysis

1. Validate Identification Rules:
   Go to CI Class Manager → cmdb_ci_computer → Identification Rule.
   Check if the rule includes strong identifiers like:

   • Serial Number

   • Fully Qualified Domain Name (FQDN)

   • BIOS UUID
     If only IP address or hostname is used, duplicates are likely because multiple MID Servers may reach the same host with different IPs.

2. Check Discovery Behavior:

   • Open the Discovery logs in the Discovery Status record.

   • Confirm whether Discovery uses multiple IPs from different IP ranges to identify the same host.

   • If yes, consolidate subnets or assign Discovery ranges to specific MID Servers based on IP segmentation or location.

3. Review Identification and Reconciliation (I&R) Rules:

   • Ensure IRE (Identification and Reconciliation Engine) is active and properly configured.

   • If you’re on a newer release (Tokyo+), make sure I&R Definition Rules are not overridden.

   • Prioritize authoritative sources (like Discovery) over imports or integrations in the Reconciliation Definitions.

4. Remediation:

   • Clean up duplicate records using Duplicate CI Remediator or a manual merge rule.

   • Adjust Discovery Schedule to avoid overlapping IP ranges.

   • Modify Identification Rule to use a stronger combination (FQDN + Serial Number).

   • Re-run Discovery and validate no new duplicates appear.

[Ravi Gaurav · Accepted solution]

And Also Below support Article will also Help you 
https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0659176

[SandeepKSingh]

Thanks for the Quick Help !!