Global IT Troubleshooting Methodology
Step Phase Name Purpose Key Keywords Concrete Example
1 Problem Identification Define the symptom objectively symptom, error code, scope, impact
2 Information Gathering Collect technical evidence logs, user input, environment
3 Scope & Impact Analysis Measure blast radius single user, global, intermittent
4 Hypothesis Formation Form testable causes root cause, probability, OSI
5 Testing & Isolation Validate or eliminate causes test, rollback, isolate
6 Root Cause Identification Explain why failure occurred underlying cause, failure mechanism
7 Resolution Implementation Apply stable fix configuration, change control
8 Verification & Monitoring Confirm resolution durability monitoring, validation
9 Documentation Preserve organizational knowledge KB, incident record
10 Prevention & Improvement Reduce recurrence risk alerting, baseline, automation
Below is a clear, simplified explanation of ITSM, followed by how ServiceNow implements it, and how APM ties into ITIL processes. This is interview-ready and operational, not theoretical.
⭐ ITSM is a structured way to design, deliver, operate, and improve IT services so they support business needs, not just technology.
Key idea:
IT is treated as a service, not a collection of servers or tickets.
Example:
❌ “We fix computers.”
✅ “We provide a reliable workplace computing service with defined response times.”
ITSM answers four core questions:
⭐ What service is provided?
⭐ Who is responsible?
⭐ How issues are handled?
⭐ How quality is measured and improved?
1️⃣ ITIL
⭐ A framework of best practices
⭐ Explains what processes should exist
⭐ Not a tool, not software
2️⃣ ITSM
⭐ The operational implementation of those practices
⭐ Can exist with or without ITIL
3️⃣ ServiceNow
⭐ An ITSM platform
⭐ Implements ITIL concepts in a workflow-based system
Short interview sentence:
“ITIL defines best practices, ITSM applies them operationally, and ServiceNow is a platform that automates ITSM workflows.”
⭐ ServiceNow is a cloud-based ITSM platform that centralizes:
⭐ Tickets
⭐ Workflows
⭐ Automation
⭐ Reporting
⭐ Configuration data
It acts as the single source of truth for IT operations.
Think of it as:
⭐ Ticketing system +
⭐ Workflow engine +
⭐ CMDB +
⭐ Reporting dashboard
Purpose: Detect issues automatically.
How ServiceNow handles it:
⭐ Monitoring tools send alerts
⭐ Events are logged
⭐ Thresholds trigger actions
Example:
CPU usage > 90% → Event generated → Possible incident created.
Purpose: Restore service as fast as possible.
ServiceNow actions:
⭐ Incident ticket creation
⭐ Priority assignment (Impact × Urgency)
⭐ SLA tracking
Example:
User cannot access email → Incident → Resolved → Closed.
Important:
Incident Management focuses on speed, not deep analysis.
Purpose: Prevent recurrence.
ServiceNow actions:
⭐ Link incidents to a problem record
⭐ Root cause analysis (RCA)
⭐ Known Error Database (KEDB)
Example:
Multiple VPN incidents → One underlying firewall misconfiguration → Permanent fix.
Key distinction:
Incident = fire extinguisher
Problem = fire prevention system
Purpose: Control risk when modifying systems.
ServiceNow actions:
⭐ Change requests (Standard / Normal / Emergency)
⭐ Approval workflows
⭐ Change calendars
Example:
Firewall rule update requires approval before deployment.
This avoids:
“Fixing one issue and breaking five others.”
Purpose: Improve services over time.
ServiceNow enables:
⭐ Metrics (MTTR, incident volume)
⭐ Trend analysis
⭐ Improvement initiatives
Example:
Repeated Wi-Fi issues → Upgrade access points → Fewer incidents.
CSI turns data into decisions.
⭐ APM observes application health in real time
⭐ It feeds ITSM processes with objective data
APM → ITIL mapping:
⭐ Event Management → Detect anomalies
⭐ Incident Management → Auto-create incidents
⭐ Problem Management → Identify recurring patterns
⭐ Change Management → Validate post-change impact
⭐ CSI → Measure performance trends
In ServiceNow:
⭐ APM alerts can automatically open incidents
⭐ Metrics populate dashboards
⭐ Correlation reduces false positives
“ITSM is the structured management of IT services; ITIL defines the best practices, and ServiceNow operationalizes them by automating incident, problem, change, and improvement workflows, often fed by monitoring tools like APM.”
1️⃣ 802.1X (Network Access Control)
⭐ Access: Permission to connect to a network
⭐ Authentication: Identity verification process
⭐ Authorization: Granting network privileges
⭐ EAP: Authentication framework
⭐ RADIUS: Centralized authentication server
⭐ Supplicant: Device requesting access
⭐ Authenticator: Switch or AP enforcing access
⭐ Port-Based: Controls physical/logical ports
⭐ Secure: Prevents unauthorized connections
⭐ Enterprise: Common in corporate networks
2️⃣ Active Directory (AD)
⭐ Directory: Central identity database
⭐ Domain: Administrative boundary
⭐ Forest: Collection of domains
⭐ LDAP: Directory access protocol
⭐ Kerberos: Ticket-based authentication
⭐ GPO: Policy enforcement mechanism
⭐ Controller: Domain authentication server
⭐ User: Identity object
⭐ Computer: Managed endpoint
⭐ Trust: Relationship between domains
3️⃣ ARP (Address Resolution Protocol)
⭐ Resolution: IP-to-MAC mapping
⭐ IP Address: Logical network identifier
⭐ MAC Address: Hardware identifier
⭐ Broadcast: Network-wide request
⭐ Request: ARP query message
⭐ Reply: MAC address response
⭐ Cache: Stored mappings
⭐ Layer 2: Data link operation
⭐ Local: Same subnet only
⭐ Spoofing: ARP poisoning attack
4️⃣ Bridge (Layer-2 Device)
⭐ Connects: Network segments
⭐ Filters: Reduces traffic
⭐ MAC-Based: Uses hardware addresses
⭐ Forwarding: Sends frames selectively
⭐ Collision Domain: Reduced size
⭐ Learning: Builds MAC table
⭐ Transparent: No host changes required
⭐ Spanning Tree: Prevents loops
⭐ Legacy: Rarely used today
⭐ LAN: Local networks
5️⃣ CI/CD Pipeline
⭐ Integration: Frequent code merging
⭐ Delivery: Automated releases
⭐ Automation: Removes manual steps
⭐ Build: Compiling code
⭐ Test: Validation stage
⭐ Deploy: Release to environment
⭐ Pipeline: Sequential workflow
⭐ Repository: Source control system
⭐ Artifact: Build output
⭐ Feedback: Test/deploy results
6️⃣ CRM (Customer Relationship Management)
⭐ Customer: Client entity
⭐ Sales: Deal tracking
⭐ Marketing: Campaign automation
⭐ Support: Case management
⭐ Database: Customer records
⭐ Analytics: Insights generation
⭐ Automation: Workflow efficiency
⭐ Integration: Connects with ERP
⭐ Lifecycle: Customer journey
⭐ Retention: Relationship management
7️⃣ DDoS (Distributed Denial of Service)
⭐ Distributed: Multiple attack sources
⭐ Denial: Service disruption
⭐ Traffic: Malicious volume
⭐ Botnet: Compromised devices
⭐ Flooding: Resource exhaustion
⭐ Amplification: Attack magnification
⭐ Mitigation: Defensive measures
⭐ Bandwidth: Saturated capacity
⭐ Availability: Targeted principle
⭐ Protection: Rate limiting, scrubbing
8️⃣ DHCP (Dynamic Host Configuration Protocol)
⭐ Automatic: No manual IP assignment
⭐ IP Address: Network identifier
⭐ Lease: Time-bound assignment
⭐ Scope: IP range pool
⭐ Server: Address distributor
⭐ Client: Requesting device
⭐ Renewal: Lease extension
⭐ Reservation: Fixed IP assignment
⭐ Option: Additional config (DNS, GW)
⭐ Broadcast: Initial discovery
9️⃣ DMARC (Email Authentication Policy)
⭐ Domain: Email identity
⭐ Policy: Fail handling rules
⭐ Alignment: Header consistency
⭐ Reporting: Authentication feedback
⭐ Authentication: Sender verification
⭐ SPF: Sender IP validation
⭐ DKIM: Message integrity
⭐ Phishing: Fraud prevention
⭐ Enforcement: Reject/quarantine actions
⭐ DNS: Policy publication
🔟 DNS (Domain Name System)
⭐ Resolution: Name-to-IP translation
⭐ Domain: Namespace segment
⭐ Query: Lookup request
⭐ Server: Resolver/authoritative
⭐ Record: A, AAAA, MX, TXT
⭐ Zone: Administrative portion
⭐ Cache: Performance optimization
⭐ Hierarchy: Root → TLD → Domain
⭐ TTL: Cache duration
⭐ Availability: Critical infrastructure
1️⃣1️⃣ DNSSEC (DNS Security Extensions)
⭐ Security: Spoofing prevention
⭐ Signature: Cryptographic proof
⭐ Validation: Authenticity check
⭐ Key: Cryptographic material
⭐ Trust Chain: Root to domain
⭐ Zone: Signed namespace
⭐ Integrity: Data protection
⭐ Authenticity: Verified origin
⭐ Record: DNSSEC-specific entries
⭐ Protection: Cache poisoning defense
1️⃣2️⃣ EDR (Endpoint Detection & Response)
⭐ Endpoint: User device
⭐ Detection: Threat identification
⭐ Response: Automated remediation
⭐ Monitoring: Continuous visibility
⭐ Behavior: Activity analysis
⭐ Threat: Malicious action
⭐ Forensics: Incident investigation
⭐ Automation: Rapid containment
⭐ Telemetry: Endpoint data
⭐ Integration: SIEM/XDR
1️⃣3️⃣ ERP (Enterprise Resource Planning)
⭐ Enterprise: Organization-wide scope
⭐ Resources: Assets and processes
⭐ Integration: Unified platform
⭐ Finance: Accounting module
⭐ HR: Workforce management
⭐ Supply Chain: Logistics tracking
⭐ Database: Centralized data
⭐ Automation: Process efficiency
⭐ Reporting: Business intelligence
⭐ Scalability: Organizational growth
1️⃣4️⃣ Firewall
⭐ Filtering: Traffic control
⭐ Rules: Allow/deny logic
⭐ Packet: Network data unit
⭐ Stateful: Connection tracking
⭐ Inspection: Payload analysis
⭐ Port: Communication endpoint
⭐ Zone: Trust boundary
⭐ NAT: Address translation
⭐ Security: Perimeter defense
⭐ Policy: Enforcement logic
1️⃣5️⃣ HTTP / HTTPS
⭐ Protocol: Web communication
⭐ Request: Client call
⭐ Response: Server reply
⭐ Stateless: No session memory
⭐ Header: Metadata container
⭐ Method: GET, POST, PUT
⭐ Port: 80 / 443
⭐ TLS: Encryption layer
⭐ Secure: HTTPS protection
⭐ Web: Application transport
1️⃣6️⃣ IaC (Infrastructure as Code)
⭐ Infrastructure: IT resources
⭐ Code: Declarative definitions
⭐ Automation: Provisioning logic
⭐ Version Control: Change tracking
⭐ Template: Reusable configs
⭐ Consistency: Environment parity
⭐ Deployment: Apply changes
⭐ Scalability: Elastic growth
⭐ Tooling: Terraform, Ansible
⭐ Auditable: Traceable changes
1️⃣7️⃣ IP Addressing
⭐ Logical: Software-assigned
⭐ IPv4: 32-bit format
⭐ IPv6: 128-bit format
⭐ Public: Internet-routable
⭐ Private: Internal-only
⭐ Static: Manual assignment
⭐ Dynamic: DHCP-based
⭐ Subnet: Network segmentation
⭐ Gateway: Exit route
⭐ Host: Device identifier
1️⃣8️⃣ IP Spoofing
⭐ Spoofing: Identity falsification
⭐ Source: Fake sender IP
⭐ Packet: Forged headers
⭐ Attack: Trust exploitation
⭐ DDoS: Common technique
⭐ Detection: Anomaly analysis
⭐ Filtering: Ingress rules
⭐ Firewall: Blocking spoofed traffic
⭐ Authentication: Source validation
⭐ Prevention: Network hygiene
1️⃣9️⃣ ITIL (IT Service Management Framework)
⭐ Framework: Best practices
⭐ Service: Value delivery
⭐ Incident: Service disruption
⭐ Problem: Root cause
⭐ Change: Controlled modification
⭐ Release: Deployment planning
⭐ Asset: Configuration item
⭐ Continual Improvement: Optimization cycle
⭐ SLA: Service commitments
⭐ Governance: Process oversight
2️⃣0️⃣ ITSM (IT Service Management)
⭐ Service: User-facing IT
⭐ Support: Helpdesk operations
⭐ Delivery: Service execution
⭐ Incident: User issue
⭐ Problem: Recurring faults
⭐ Change: Controlled updates
⭐ Asset: Hardware/software tracking
⭐ Request: User demand
⭐ Workflow: Process automation
⭐ Customer: End user
2️⃣1️⃣ Load Balancing
⭐ Load: Incoming requests
⭐ Distribution: Traffic spreading
⭐ Algorithm: Round-robin, least-conn
⭐ Server: Backend node
⭐ Availability: Uptime assurance
⭐ Redundancy: Failover design
⭐ Health Check: Node monitoring
⭐ Scalability: Horizontal growth
⭐ Performance: Response optimization
⭐ Resilience: Fault tolerance
2️⃣2️⃣ Malware (General Category)
⭐ Malicious: Harmful intent
⭐ Virus: Host-dependent
⭐ Worm: Self-propagating
⭐ Trojan: Disguised payload
⭐ Ransomware: Encrypted extortion
⭐ Spyware: Data theft
⭐ Adware: Unwanted advertising
⭐ Payload: Malicious code
⭐ Detection: AV/EDR tools
⭐ Prevention: Patching, awareness
2️⃣3️⃣ Phishing
⭐ Social Engineering: Human exploitation
⭐ Email: Primary vector
⭐ Spoofing: Fake sender
⭐ Link: Malicious URL
⭐ Attachment: Infected file
⭐ Credentials: Targeted data
⭐ Awareness: User training
⭐ Filtering: Email gateways
⭐ Reporting: Incident response
⭐ Simulation: Training campaigns
2️⃣4️⃣ Ransomware
⭐ Encryption: Data locking
⭐ Ransom: Payment demand
⭐ Cryptocurrency: Payment method
⭐ Attack Vector: Phishing, RDP
⭐ Backup: Recovery mechanism
⭐ Decryption: Key release
⭐ Downtime: Business impact
⭐ Prevention: Security controls
⭐ Response: Incident handling
⭐ Recovery: System restoration
2️⃣5️⃣ SIEM (Security Information & Event Management)
⭐ Logs: Collected events
⭐ Correlation: Pattern detection
⭐ Alerting: Threat notification
⭐ Dashboard: Security visibility
⭐ Compliance: Regulatory support
⭐ Retention: Log storage
⭐ Analytics: Threat analysis
⭐ Automation: SOAR integration
⭐ Integration: Multiple sources
⭐ Monitoring: Central oversight
2️⃣6️⃣ SSL / TLS
⭐ Encryption: Data protection
⭐ Certificate: Identity proof
⭐ CA: Certificate authority
⭐ Handshake: Secure setup
⭐ Asymmetric: Key exchange
⭐ Symmetric: Session encryption
⭐ Authentication: Server verification
⭐ Integrity: Data protection
⭐ HTTPS: Secure web traffic
⭐ Trust: PKI model
2️⃣7️⃣ Subnetting
⭐ Segmentation: Network division
⭐ Mask: Address boundary
⭐ CIDR: Notation standard
⭐ Broadcast: Subnet-wide traffic
⭐ Range: IP allocation
⭐ Isolation: Traffic control
⭐ Routing: Inter-subnet paths
⭐ Efficiency: Address optimization
⭐ Design: Network planning
⭐ Security: Reduced exposure
2️⃣8️⃣ VPN (Remote & Site-to-Site)
⭐ Tunnel: Encrypted channel
⭐ Encryption: Data security
⭐ Authentication: Identity verification
⭐ Remote Access: User connectivity
⭐ Site-to-Site: Network linking
⭐ IPSec: Secure protocol
⭐ SSL: Application-layer VPN
⭐ Gateway: Tunnel endpoint
⭐ Routing: Private traffic flow
⭐ Confidentiality: Data privacy
2️⃣9️⃣ XDR (Extended Detection & Response)
⭐ Extended: Multi-layer scope
⭐ Endpoint: Device telemetry
⭐ Network: Traffic analysis
⭐ Cloud: SaaS/IaaS coverage
⭐ Detection: Threat discovery
⭐ Response: Automated actions
⭐ Correlation: Cross-domain events
⭐ Analytics: Advanced insights
⭐ Automation: Rapid mitigation
⭐ Visibility: Unified security view
⭐ Active Directory — Central identity store
⭐ LDAP — Directory query protocol
⭐ Kerberos — Ticket-based authentication
⭐ SSO / OAuth — Token-based access
⭐ 802.1X — Network access enforcement
Rule: If identity fails, stop here.
⭐ IP Addressing — Logical device identity
⭐ Subnetting — Network segmentation
⭐ ARP — IP → MAC resolution
⭐ Routing — Path selection
⭐ NAT — Private ↔ Public translation
Rule: No IP path = no application.
⭐ DNS / DNSSEC — Name resolution + trust
⭐ DHCP — IP assignment
⭐ NTP — Time synchronization
Rule: Time + DNS failures mimic “random bugs.”
⭐ HTTP / HTTPS — Web transport
⭐ SMB — File sharing
⭐ RDP — Remote access
⭐ CRM / ERP — Business systems
Rule: Apps are symptoms, not roots.
⭐ Load Balancing — Traffic distribution
⭐ Health Checks — Node validation
⭐ Redundancy — Failure tolerance
Rule: Users notice uptime before security.
⭐ IaC — Infrastructure as code
⭐ CI/CD — Automated delivery
⭐ VPC — Isolated cloud network
Rule: Misconfigurations scale instantly.
⭐ Phishing — Credential theft
⭐ Malware — Malicious code
⭐ Ransomware — Encrypted extortion
⭐ DDoS — Service flooding
⭐ IP Spoofing — Identity forgery
Rule: Most attacks start with humans.
⭐ Event Logs — Raw signals
⭐ SIEM — Correlation engine
⭐ EDR — Endpoint defense
⭐ XDR — Cross-domain visibility
Rule: Security = patterns over time.
⭐ ITIL — Best-practice framework
⭐ ITSM — Operational execution
⭐ Incident / Problem / Change
Rule: Process prevents repeat outages.
Symptoms:
⭐ VPN connects successfully
⭐ Login fails immediately
Correct reasoning path:
⭐ VPN OK → Network OK
⭐ Authentication failure → AD / Kerberos
⭐ Check time sync (NTP)
⭐ Check domain trust
Interview-grade answer:
“I would verify NTP synchronization first, then validate Kerberos ticket issuance in Active Directory.”
Symptoms:
⭐ Page loads intermittently
⭐ No error messages
Reasoning path:
⭐ DNS resolves
⭐ HTTP works
⭐ Suspect load balancer health checks
⭐ Check backend saturation
Key concept tested: Availability ≠ functionality
Symptoms:
⭐ Password resets don’t help
Reasoning path:
⭐ Possible phishing
⭐ SIEM login anomaly correlation
⭐ Disable sessions
⭐ Enforce credential reset
Key concept tested: Security incident recognition
Symptoms:
⭐ Ransom note
⭐ Shared drives affected
Reasoning path:
⭐ Isolate endpoint (EDR)
⭐ Disable SMB shares
⭐ Restore from backups
⭐ Trigger incident process
Key concept tested: Containment over curiosity
Symptoms:
⭐ Outbound emails rejected
Reasoning path:
⭐ Check SPF record
⭐ Validate DKIM signature
⭐ Review DMARC policy
Key concept tested: Email trust chain
Below is a professional troubleshooting methodology, used in ITIL-aligned environments, explained step by step, with concrete examples, common mistakes, and language improvements.
This is exactly what interviewers expect you to implicitly follow when you answer scenario questions.
⭐ Goal: Understand the issue without guessing
What to do:
⭐ Listen actively to the user
⭐ Capture exact symptoms, not interpretations
⭐ Identify scope: single user, multiple users, entire service
⭐ Determine timing: when it started, what changed
Bad example (user statement):
❌ “The network is down.”
Your correction (professional reframing):
✅ “The user cannot access internal resources after connecting to VPN.”
Concrete questions:
⭐ What error message is displayed?
⭐ Does it affect others?
⭐ Did anything change (update, password, device)?
⚠️ Common mistake:
Jumping to solutions before defining the problem.
Language tip (English):
Replace vague verbs like “doesn’t work” with observable actions:
⭐ fails to authenticate
⭐ times out
⭐ cannot resolve hostname
⭐ Goal: Form hypotheses based on evidence
Use layered logic, not intuition:
⭐ Identity layer (login, credentials, MFA)
⭐ Network layer (IP, DNS, routing)
⭐ Application layer (service availability)
Example:
⭐ VPN connects successfully
⭐ Login to internal app fails
Correct theory:
✅ Network connectivity exists → suspect authentication or authorization
Wrong theory:
❌ “Internet problem”
⚠️ Common mistake:
Blaming “the network” when identity or DNS is failing.
Interview phrasing upgrade:
❌ “It might be a server issue.”
✅ “Since connectivity is established, I would investigate authentication services next.”
⭐ Goal: Confirm or disprove the hypothesis safely
Start with low-risk tests:
⭐ Ping (connectivity)
⭐ nslookup / dig (DNS resolution)
⭐ Login test with known-good account
⭐ Check system time (NTP)
Example:
⭐ User cannot log in
⭐ Check system clock
⭐ Time drift found → Kerberos fails
Theory confirmed.
⚠️ Common mistake:
⭐ Making changes before validating cause
⭐ Restarting services blindly
Keyboard shortcuts (Windows):
⭐ Win + R → eventvwr.msc
⭐ Win + X → Event Viewer / PowerShell
⭐ Ctrl + Shift + Esc → Task Manager
⭐ Goal: Fix with minimal impact
Plan includes:
⭐ What will be changed
⭐ Expected outcome
⭐ Rollback plan
Example:
⭐ Action: Sync system time with domain controller
⭐ Expected: Kerberos authentication succeeds
⭐ Rollback: Revert time source if sync fails
Professional wording:
✅ “I would apply a targeted fix and monitor authentication logs.”
⚠️ Common mistake:
Fixing symptoms instead of root cause.
⭐ Goal: Execute precisely, document implicitly
Actions:
⭐ Apply fix
⭐ Monitor immediately
⭐ Avoid unrelated changes
Example:
⭐ Force NTP sync
⭐ User logs in successfully
⚠️ Common mistake:
Applying multiple fixes at once → no root cause clarity.
⭐ Goal: Ensure the issue is fully resolved
Check:
⭐ Original symptom resolved
⭐ No side effects
⭐ Related services still work
Example:
⭐ Login works
⭐ Access to file shares verified
⭐ VPN stable
Interview phrasing:
✅ “I would confirm the issue is resolved and validate dependent services.”
⭐ Goal: Turn incident into knowledge
Document:
⭐ Root cause
⭐ Resolution
⭐ Preventive action
Example:
⭐ Root cause: Time drift on endpoint
⭐ Prevention: Enforce NTP via GPO
Why interviewers love this step:
⭐ Shows maturity
⭐ Shows process awareness
⭐ Shows long-term thinking
Never troubleshoot from the top (application) before validating the bottom (identity, DNS, time, IP).
Below is a global IT troubleshooting methodology, deliberately vendor-neutral and aligned with ITIL / real-world helpdesk practice. Each step explains what, why, and how, with concrete examples. This is the mental algorithm senior analysts actually run, even if informally.
1️⃣ Problem Identification (Define the symptom, not the theory)
🎯 Goal: Describe what is failing without assuming the cause.
Why: Most troubleshooting errors come from jumping to conclusions.
Example:
❌ “The VPN is broken.”
✅ “User cannot establish a VPN connection; error 809 appears after authentication.”
Key points:
⭐ Separate symptoms from interpretations
⭐ Capture exact error messages, timestamps, and scope (one user vs many)
⭐ Ask what changed recently (updates, hardware, policy)
Language tip (English):
Prefer concrete verbs.
Instead of “doesn’t work” → “fails to connect,” “times out,” “returns error X”.
2️⃣ Information Gathering (Build the evidence base)
🎯 Goal: Collect facts from multiple layers before acting.
Why: IT systems fail across layers; guessing wastes time.
Sources:
⭐ User input (what they did, step-by-step)
⭐ System logs (Event Viewer, syslog, application logs)
⭐ Monitoring tools (CPU, memory, disk, network latency)
⭐ Environment details (OS version, network type, permissions)
Example:
VPN issue → Check:
⭐ User’s network (home Wi-Fi vs corporate LAN)
⭐ Firewall logs
⭐ VPN client version
⭐ Authentication logs (AD / Azure AD)
Keyboard shortcuts:
⭐ Windows Event Viewer: Win + R → eventvwr.msc
⭐ Network info: ipconfig /all
⭐ Quick connectivity test: ping, tracert
3️⃣ Scope and Impact Analysis (Isolate the blast radius)
🎯 Goal: Determine how big the problem is.
Why: A single-user issue ≠ a system outage.
Questions to answer:
⭐ One user or many?
⭐ One device or all devices?
⭐ One location or global?
⭐ Intermittent or constant?
Example:
If only one user fails VPN → likely local config.
If all users fail → infrastructure, certificate, or service outage.
This step protects you from wasting time debugging laptops when the server is down.
4️⃣ Hypothesis Formation (Structured guessing, not intuition)
🎯 Goal: Propose testable causes, ordered by probability.
Why: Random fixes create instability.
Rule of thumb:
⭐ Start with simplest + most common causes
⭐ Follow the OSI / stack order (Physical → Application)
Example hypotheses for “VPN error 809”:
Firewall blocking ports
VPN service stopped
Certificate expired
DNS resolution failure
Important:
A hypothesis must be falsifiable.
“If I test X and it works, hypothesis is wrong.”
5️⃣ Testing & Isolation (Change one variable at a time)
🎯 Goal: Prove or eliminate each hypothesis.
Why: Multiple simultaneous changes destroy traceability.
Good practice:
⭐ One change → one test → observe result
⭐ Roll back if unsuccessful
⭐ Document outcomes
Example:
Disable firewall temporarily → test VPN
If VPN connects → firewall rule confirmed as root cause.
Automation tip:
⭐ PowerShell: Test-NetConnection -Port 443 -ComputerName vpn.company.com
6️⃣ Root Cause Identification (The “why”, not the “what”)
🎯 Goal: Identify the underlying failure mechanism.
Why: Fixing symptoms causes recurrence.
Bad root cause:
❌ “User couldn’t connect.”
Good root cause:
✅ “Firewall policy update blocked UDP 500/4500 for VPN traffic.”
This is where junior vs senior analysts diverge.
7️⃣ Resolution Implementation (Correct + stabilize)
🎯 Goal: Apply a fix that resolves the issue without side effects.
Why: Emergency fixes can create new incidents.
Best practices:
⭐ Prefer configuration over workaround
⭐ Follow change management if production systems are involved
⭐ Validate with the user
Example:
Add firewall exception → restart VPN service → user confirms access.
8️⃣ Verification & Monitoring (Trust, but verify)
🎯 Goal: Ensure the problem is truly resolved.
Why: Some failures are delayed or intermittent.
Actions:
⭐ Reproduce original scenario
⭐ Monitor logs for recurrence
⭐ Confirm performance, not just functionality
Example:
VPN connects AND remains stable for 15–30 minutes.
9️⃣ Documentation & Knowledge Sharing (Future-proofing)
🎯 Goal: Make the next incident faster to solve.
Why: Undocumented fixes are lost knowledge.
Document:
⭐ Symptoms
⭐ Root cause
⭐ Resolution steps
⭐ Prevention actions
Example:
Internal KB article:
“VPN Error 809 after firewall update – required ports and fix.”
🔟 Prevention & Continuous Improvement (Engineering mindset)
🎯 Goal: Reduce probability of recurrence.
Why: The best incident is the one that never happens.
Actions:
⭐ Monitoring alerts
⭐ Configuration baselines
⭐ Change impact analysis
⭐ User education
Example:
Alert on certificate expiration 30 days before failure.
Troubleshooting is not “trying fixes”.
It is applied logic under uncertainty, constrained by time, risk, and evidence.
If you want, we can map this exact methodology to:
⭐ Helpdesk Level 1 interview answers
⭐ ITIL Incident vs Problem Management
⭐ Network-only or Application-only scenarios
Would you like this methodology adapted specifically for remote bilingual IT helpdesk interviews (Yes/No)?