🚀 ServiceNow Discovery & CMDB Interview Questions and Answers (2025)

[Ravi Gaurav]

Hello ServiceNow Family, this is Ravi and I am back with great article of 2025 related to ServiceNow ITOM

Are you preparing for a ServiceNow ITOM (Discovery/CMDB) interview? Understanding how Discovery and the Configuration Management Database (CMDB) work is key to managing IT infrastructure efficiently. Below are the most frequently asked questions from real-world interviews, curated with clear and updated answers.

🔖 Note: These answers are framed based on personal knowledge and real-time interview experiences over the past year. The wording may vary depending on individual understanding.

✅ Q1: What is Discovery? What are the types of Discovery in ServiceNow?

Answer:
Discovery is the process of identifying IT assets (servers, applications, network devices, etc.) and populating them into the CMDB.
Types:

• Horizontal Discovery: Identifies infrastructure components like servers, routers, switches.

• Top-Down Discovery (Service Mapping): Maps business services and the relationships between their components.

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✅ Q2: Explain the phases of Discovery.

Answer:

1. Scanning – Detects live IP addresses and open ports.

2. Classification – Determines the type of device (Linux, Windows, etc.).

3. Identification – Checks if a CI already exists or creates a new one.

4. Exploration – Gathers detailed info about the device.

5. Dependency Mapping – Identifies relationships between CIs.

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✅ Q3: What is Scheduled Discovery?

Answer:
Scheduled Discovery allows Discovery jobs to run automatically at defined intervals, ensuring the CMDB remains updated consistently.

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✅ Q4: What are the types of Horizontal Discovery?

Answer:

• Infrastructure Discovery: Identifies physical/virtual servers, storage, network hardware.

• Application Discovery: Discovers applications and software services running on the devices.

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✅ Q5: Explain MID Server configuration.

Answer:
MID (Management, Instrumentation, and Discovery) Server is a lightweight Java application installed behind the firewall to facilitate communication between ServiceNow and target systems.
Configuration includes:

• Installing on a Windows/Linux server.

• Registering with instance.

• Assigning capabilities (Discovery, Orchestration, etc.).

• Defining IP ranges and credentials.

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✅ Q6: What if there's an issue in the scanning phase?

Answer:

• Check MID Server logs.

• Validate IP ranges and credentials.

• Ensure firewall is not blocking required ports.

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✅ Q7: Where do you troubleshoot Discovery issues?

Answer:

• ECC Queue: For communication errors.

• MID Server logs: To analyze command execution.

• Discovery Log: Review Discovery status and phase failures.

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✅ Q8: How do you check the MID Server status?

Answer:
Navigate to: MID Server > Servers
Look for statuses like Up, Down, Validated, or Validating.

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✅ Q9: What are probes, sensors, and patterns?

Answer:

• Probes: Scripts that collect data.

• Sensors: Process probe results and populate CMDB.

• Patterns: Declarative models for Discovery and Service Mapping without needing scripts.

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✅ Q10: What is “Help the Help Desk”?

Answer:
A feature that gives IT support teams quick access to relevant CI details for faster incident resolution.

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✅ Q11: How is communication done between MID Server and Discovery?

Answer:
Through the ECC Queue.

• ServiceNow sends instructions (input) → MID Server

• MID executes probes and returns results (output) → ServiceNow

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✅ Q12: What does the ECC Queue contain?

Answer:

• Input: Tasks sent to MID Server.

• Output: Results returned from MID Server.

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✅ Q13: What credentials are used for devices?

Answer:

• Windows: WMI

• Linux/Unix: SSH

• Network devices: SNMP

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✅ Q14: How to discover network devices using Network Configuration Manager?

Answer:

• Add devices to Discovery Schedule.

• Assign SNMP credentials.

• Run Discovery job to fetch config via SNMP.

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✅ Q15: What is Knowledge Discovery?

Answer:
It refers to the process of generating insights from data in CMDB—like relationships, usage, trends.

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✅ Q16: What ports must be open for SSH and WMI Discovery?

Answer:

• SSH: Port 22

• WMI (Windows): Ports 135, 445, and dynamic ports (1024–65535)

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✅ Q17: What are Discovery behaviors?

Answer:
Behaviors define how Discovery interacts with devices using protocols like SSH, SNMP, WMI, etc.

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✅ Q18: If a device supports both SSH and SNMP, which is used?

Answer:
Depends on Discovery behavior configuration. Typically:

• SNMP: For network devices.

• SSH: For Linux/Unix servers.

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✅ Q19: Can a Windows MID Server discover Linux machines?

Answer:
Yes. It can use SSH to discover Linux/Unix machines.

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✅ Q20: What is MID Server Clustering?

Answer:
A group of MID Servers acting together for load balancing and failover support.

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✅ Q21: Difference between Discovery and Service Mapping?

Answer:

• Discovery: Finds infrastructure and populates CMDB.

• Service Mapping: Identifies application dependencies and maps complete services.

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✅ Q22: What are the various phases in Discovery?

Answer:

1. Scanning

2. Classification

3. Identification

4. Exploration

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✅ Q23: Difference between TCP and UDP?

Answer:

• TCP: Reliable, error-checked, slower.

• UDP: Faster, but no guarantee of delivery.

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✅ Q24: How to find IP address on UNIX?

Answer:

• ifconfig (Unix)

• ip a or hostname -I (Linux)

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💡 Other Common CMDB Questions

✅ What are the base CMDB tables?

• cmdb: Core CMDB table

• cmdb_ci: Base CI table

• cmdb_rel_ci: Stores CI relationships

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✅ Tables that extend cmdb_ci_server?

Examples:

• cmdb_ci_linux_server

• cmdb_ci_win_server

• cmdb_ci_virtualization_server

• cmdb_ci_mainframe, cmdb_ci_osx_server, etc.

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✅ Where is data center info stored?

Answer:
In table: cmdb_ci_datacenter

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✅ How to test CMDB health?

Use CMDB Dashboard and configure KPIs:

• Completeness

• Correctness

• Compliance

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✅ What are Identification Rules?

Rules used to determine if a CI is unique and already exists in the CMDB using:

• Unique attributes (e.g., serial number)

• Required attributes (e.g., name, company)

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✅ What are Reconciliation Rules?

Define which data source can update CMDB records and attribute precedence when multiple sources exist.

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✅ What roles are required to manage CMDB?

Role	Description
sn_cmdb_admin	Full CMDB admin rights
sn_cmdb_editor	Edit access
sn_cmdb_user	Read-only
cmdb_import_api_admin	Import set REST access
cmdb_query_builder	Build CMDB queries

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✅ Have you implemented Discovery?

Tip: Share:

• MID installation/config steps

• Issues faced and resolved

• Tools integrated (e.g., SCCM, Tanium, TADDM)

• Volume and scale (e.g., number of CIs discovered)

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✅ Best Practices for CMDB Implementation

• Use OOB CI Classes

• Avoid heavy customizations

• Leverage CMDB Health Dashboard

• Use Identification & Reconciliation rules

• Assign CI ownership

• Automate population using Discovery & Integrations
  

[Ravi Gaurav]

Thanks @Everyone for Liking this Article. Many more to come

[sagargurram]

Good

[KarthikeyaM007]

Very helpful. Thanks Ravi

[sagargurram]

Thanks Ravi

[Deep_delhi]

Very helpful Thank you so much 

[Rajeswari R]

Very helpful! Thanks Ravi

[Ziad Elawar2]

Excellent thank you for sharing and prepapring these questions

[srujank11067885]

Thanks for sharing, It's very helpful!