Serial Numbers are not getting populated in CMDB table using ServiceNow discovery

Shraddha Dube
Tera Contributor

‎05-28-2025 09:24 AM

Hello,

 

In Network Node class, for some records Serial number is missing in cmdb table using discovery.

Why it missing for few and others populating the serial numbers for IP Routers and IP switches?

Please help me to troubleshoot this issue  as I am new to Discovery Module.

 

Thanks in advance!!

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Selva Arun
Mega Sage
Mega Sage

‎05-28-2025 01:14 PM

Hi @Shraddha Dube ,

 

This is a common issue when working with ServiceNow Discovery, especially for network devices like routers and switches. Here are some possible reasons why serial numbers might be missing for some records but not others, along with troubleshooting steps:

Troubleshooting Steps for Missing Serial Numbers

A. Verify Credentials

B. Manually Query the Serial Number OID Using SNMP Tools

  • Use snmpwalk to check if the device returns a serial number.
  • Common OIDs for serial numbers:
    • For most vendors: 1.3.6.1.2.1.47.1.1.1.1.11
    • For Cisco: 1.3.6.1.4.1.9.3.6.3
  • Example command:
    snmpwalk -v2c -c <community> <device_ip> 1.3.6.1.2.1.47.1.1.1.1.11
  • If the serial number is not returned, the device may not expose it via SNMP.

C. Debug the Discovery Pattern and Check the Payload

  • Go to Discovery Patterns in ServiceNow.
  • Find and open the pattern used for the device class (e.g., Network Switch, IP Router).
  • Click Try Pattern or Debug Pattern (depending on your version).
  • Enter the IP address of the affected device and run the pattern in debug mode.
  • Step through the pattern to the SNMP step that retrieves the serial number.
  • Check the Variables panel to see if the serial number variable is populated.
  • At the end of the run, review the Payload tab to see if the serial number is included in the data sent to the sensor.
  • For more information on debugging patterns, see:
    https://docs.servicenow.com/bundle/utah-it-operations-management/page/product/discovery/task/debug-d...

D. Inspect the ECC Queue and Discovery Log

E. Validate Network Connectivity

  • Ensure SNMP (UDP 161) is open between the MID Server and the device.
  • Use snmpwalk from the MID Server to confirm connectivity.

F. Check Device Firmware and MIB Support

  • Some devices may use proprietary OIDs for serial numbers.
  • Consult the device documentation or vendor support for the correct OID.
  • If needed, add a custom step in the Discovery Pattern to retrieve the serial number from the correct OID.

Additional Resources

If you believe the solution provided has adequately addressed your query, could you please mark it as 'Helpful' and 'Accept it as a Solution'? This will help other community members who might have the same question find the answer more easily.

Thank you for your consideration.

 

Selva Arun

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