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

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.

✅ Q2: Explain the phases of Discovery.

Answer:

Scanning – Detects live IP addresses and open ports.
Classification – Determines the type of device (Linux, Windows, etc.).
Identification – Checks if a CI already exists or creates a new one.
Exploration – Gathers detailed info about the device.
Dependency Mapping – Identifies relationships between CIs.

✅ Q3: What is Scheduled Discovery?

Answer:

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

✅ 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.

✅ 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.

✅ 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.

✅ 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.

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

Answer:

Navigate to: MID Server > Servers

Look for statuses like Up, Down, Validated, or Validating.

✅ 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.

✅ 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.

✅ 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

✅ Q12: What does the ECC Queue contain?

Answer:

Input: Tasks sent to MID Server.
Output: Results returned from MID Server.

✅ Q13: What credentials are used for devices?

Answer:

Windows: WMI
Linux/Unix: SSH
Network devices: SNMP

✅ 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.

✅ Q15: What is Knowledge Discovery?

Answer:

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

✅ 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)

✅ Q17: What are Discovery behaviors?

Answer:

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

✅ 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.

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

Answer:

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

✅ Q20: What is MID Server Clustering?

Answer:

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

✅ Q21: Difference between Discovery and Service Mapping?

Answer:

Discovery: Finds infrastructure and populates CMDB.
Service Mapping: Identifies application dependencies and maps complete services.

✅ Q22: What are the various phases in Discovery?

Answer:

Scanning
Classification
Identification
Exploration

✅ Q23: Difference between TCP and UDP?

Answer:

TCP: Reliable, error-checked, slower.
UDP: Faster, but no guarantee of delivery.

✅ Q24: How to find IP address on UNIX?

Answer:

ifconfig (Unix)
ip a or hostname -I (Linux)

💡 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

✅ 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.

✅ Where is data center info stored?

Answer:

In table: cmdb_ci_datacenter

✅ How to test CMDB health?

Use CMDB Dashboard and configure KPIs:

Completeness
Correctness
Compliance

✅ 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)

✅ What are Reconciliation Rules?

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

✅ 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

✅ 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)

✅ 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

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

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

✅ Q2: Explain the phases of Discovery.

✅ Q3: What is Scheduled Discovery?

✅ Q4: What are the types of Horizontal Discovery?

✅ Q5: Explain MID Server configuration.

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

✅ Q7: Where do you troubleshoot Discovery issues?

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

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

✅ Q10: What is “Help the Help Desk”?

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

✅ Q12: What does the ECC Queue contain?

✅ Q13: What credentials are used for devices?

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

✅ Q15: What is Knowledge Discovery?

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

✅ Q17: What are Discovery behaviors?

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

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

✅ Q20: What is MID Server Clustering?

✅ Q21: Difference between Discovery and Service Mapping?

✅ Q22: What are the various phases in Discovery?

✅ Q23: Difference between TCP and UDP?

✅ Q24: How to find IP address on UNIX?

💡 Other Common CMDB Questions

✅ What are the base CMDB tables?

✅ Tables that extend cmdb_ci_server?

✅ Where is data center info stored?

✅ How to test CMDB health?

✅ What are Identification Rules?

✅ What are Reconciliation Rules?

✅ What roles are required to manage CMDB?

✅ Have you implemented Discovery?

✅ Best Practices for CMDB Implementation

✅ Tables that extend `cmdb_ci_server`?