VPN & NW Troubleshooting 🖇️

🧠 Key Networking Concepts to Understand:

1️⃣ Subnets:
Understand how IP addressing works within subnets — how IP ranges are divided and how devices communicate within and across subnets.

2️⃣ IP Address Assignment:
Know how a device gets its IP address (DHCP vs static), and how this ties into the local network and connectivity troubleshooting.

3️⃣ Default Gateway:
The gateway is essential for routing traffic outside the local network. Misconfigured gateways are a common cause of connectivity issues.

4️⃣ DNS (Domain Name System):
Understand how DNS resolves domain names to IP addresses, and how to troubleshoot when DNS issues occur (e.g., nslookup, alternate DNS like 1.1.1.1 or 8.8.8.8).

5️⃣ Traffic Flow Verification:
Be able to trace packets from one device to another using tools like:

• ping
  
  

• tracert or traceroute
  
  

• ipconfig /all
  
  

• netstat
  
  

• pathping
  
  

6️⃣ Critical Windows Commands:

• 🖥️ ncpa.cpl: Quickly opens the Network Connections panel to view and edit adapters.
  
  

• 🔁 Network Reset (Settings > Network & Internet > Status > Network Reset): Resets all network components to defaults — especially useful when drivers or configurations are corrupted.
  
  

📌 Tip: Practice using these commands in different troubleshooting scenarios. Simulate issues by disabling DHCP, changing DNS manually, or misconfiguring gateways to learn how each impacts connectivity.

🎯 Rewritten version of your original message (more concise & professional):

A strong grasp of subnetting, IP address assignment, default gateways, and DNS is essential. These fundamentals allow us to trace and verify device-to-device connectivity effectively. In Windows environments, tools like ncpa.cpl and the built-in Network Reset feature are critical for quick diagnostics and resolution. I recommend practicing these hands-on to become fluent in real-world troubleshooting.

📝 English Correction & Writing Tips (based on your original draft):

Issues Detected:

• Informal phrasing: “absolutely clutch” → too casual for professional use.
  
  

• Redundant or vague: “That’s what we’re constantly using” → unclear subject.
  
  

• Overuse of conjunctions: Try separating ideas with punctuation.
  
  

Writing Improvement Tips:

✅ Avoid vague pronouns — specify what "that" or "those" refers to.
✅ Use parallel structure: when listing concepts, match the format.
✅ Prefer action verbs: “verify”, “understand”, “trace”, “reset” instead of “thing to understand”.
✅ Maintain professional tone for clarity and credibility.

📚 Prompt Engineering Tip:
When creating technical prompts, add “from a help desk technician’s perspective” or “include practical troubleshooting steps” to get more targeted outputs.

❓Would you like to go deeper into how to analyze traffic with tools like Wireshark, PowerShell, or packet capture on Windows?

What is pathping

🛰️ What Is pathping?

pathping is a Windows command-line network utility that combines the features of both ping and tracert. It helps you:

🔹 Identify packet loss
🔹 Detect network latency
🔹 Pinpoint which hop (router or node) along the path is causing problems

It’s more powerful than ping or tracert alone because it analyzes each hop over time (25 seconds by default) to give packet loss statistics per node.

🧪 Syntax

pathping [destination]

Example:

pathping google.com

🧰 What It Does — Step-by-Step:

1️⃣ Performs a Traceroute

• Identifies each hop from your device to the target (like tracert)
  
  

2️⃣ Pings Each Hop Repeatedly

• Sends multiple pings over ~25 seconds
  
  

• Gathers latency (RTT) and packet loss at each hop
  
  

3️⃣ Displays a Detailed Report

• Shows where the connection might be failing or slowing down
  
  

📊 Example Output:

Tracing route to google.com over a maximum of 30 hops

0  my-computer.local [192.168.1.100]

1  192.168.1.1

2  100.64.0.1

3  ...

Computing statistics for 125 seconds...

Hop RTT     Lost/Sent = Pct  Address

1   1ms     0/100 =  0%     192.168.1.1

2   12ms    0/100 =  0%     100.64.0.1

3   78ms    5/100 =  5%     203.0.113.9

...

This shows Hop 3 is experiencing 5% packet loss, which could indicate network congestion or instability.

📌 Use Cases for Helpdesk / IT Support:

✅ Diagnosing slow or dropped connections
✅ Checking for ISP or middle-node issues
✅ Troubleshooting VPN tunnels or multi-hop latency

⌨️ Keyboard Shortcuts & Usage Tips:

• 🚀 Run Command Prompt as Admin: Ctrl + Shift + Enter (from Start Menu search)
  
  

• 🛠️ Export results to file:
  
  

pathping google.com > results.txt

• 🎯 Combine with:
  
  

  • ipconfig /all (to verify adapter info)
    
    

  • netsh int ip reset (to reset network stack)
    
    

  • ping and tracert for quick checks
    
    

📝 English Improvement from Your Original Use:

Original:

“And then those two commands, ncpa.cpl in Windows, and network reset. Absolutely clutch. Try it out. Practice it yourself.”

Improved:

“Commands like ncpa.cpl and Network Reset in Windows are essential tools for troubleshooting. I recommend practicing these to build confidence in real scenarios.”

🔍 Would you like a visual guide comparing ping, tracert, and pathping, with use cases and when to use each? Yes/No?

Yes

Here’s a detailed 🧠 Visual Comparison Guide of ping, tracert, and pathping — focused on when to use each, their functions, and real-world helpdesk examples:

🧰 Tool Comparison Table

Feature / Tool

ping 📶

tracert 🗺️

pathping 📊

Checks basic connectivity

✅ Yes

⚠️ Indirectly

✅ Yes

Shows route (hops)

❌ No

✅ Yes

✅ Yes

Measures latency

✅ Yes (RTT only)

✅ Yes (per hop)

✅ Yes (per hop, average)

Detects packet loss

⚠️ Yes (total loss)

⚠️ Yes (guesswork)

✅ Yes (per hop stats)

Time to complete

⚡ Fast (few sec)

🕓 Medium (10-30 sec)

🐢 Slow (~2–3 min)

Ideal for

Quick checks

Route discovery

Deep diagnostics

🧪 Command Usage Breakdown

1️⃣ ping – Basic Connectivity Test

Command:

ping google.com

🔹 Use to check if a host is reachable
🔹 Measures round-trip time (RTT)
🔹 Useful for confirming if internet works at all

✅ Best For:

• "Is this site up?"
  
  

• "Do I have any connection?"
  
  

2️⃣ tracert – Route Mapping

Command:

tracert google.com

🔹 Lists all hops between source and destination
🔹 Shows each router's IP address and delay
🔹 Can indicate where delay begins

✅ Best For:

• "Where is the network slowing down?"
  
  

• "Is the problem with my ISP?"
  
  

3️⃣ pathping – Deep Diagnostics

Command:

pathping google.com

🔹 Combines ping + tracert
🔹 Tests each hop for latency and packet loss over time
🔹 Wait time: up to 125 seconds

✅ Best For:

• Intermittent disconnects
  
  

• VPN issues
  
  

• VoIP call drops
  
  

• Gaming lag diagnostics
  
  

🖥️ Use Case Flow Example (Helpdesk Level 1)

👨‍💻 User: "I keep losing connection to Teams calls randomly."

1️⃣ ping teams.microsoft.com
→ No packet loss? Move on.
→ 100% loss? No internet — escalate to ISP/router issue.

2️⃣ tracert teams.microsoft.com
→ Delays start at hop 3? Possibly a bad router or congested node.

3️⃣ pathping teams.microsoft.com
→ Shows 18% packet loss at a specific hop? That hop is likely the issue.

🔧 Tips & Tricks

🔹 Use > filename.txt to save results:

pathping google.com > report.txt

🔹 Run cmd as Admin for full access:
Shortcut: Search for cmd → Ctrl + Shift + Enter

🔹 Combine tools in a PowerShell script to automate:

ping google.com

tracert google.com

pathping google.com

📝 English Correction Example (Your Draft):

Original:

“Try it out. Practice it yourself. Let me know what you think.”

Improved:

“I recommend testing these tools in real scenarios to understand how they work and where to apply them effectively.”

📘 Prompt Engineering Tip:
When asking about tools, use:

“Explain like I’m troubleshooting VPN or VoIP”
to get practical, scenario-based guidance.

Would you like me to generate a PowerShell script template for automating ping + tracert + pathping for helpdesk use? Yes/No?

yes

Below is a production-ready PowerShell helpdesk script that automates ping, tracert, and pathping, saves results to a timestamped report, and highlights what matters during triage. This is the kind of thing Level-1 and Level-2 teams actually reuse.

🧪 PowerShell Network Diagnostic Script (Helpdesk-Ready)

# ===========================

# Network Diagnostic Script

# Tools: ping, tracert, pathping

# Author: Jonathan Decelles (template-ready)

# ===========================

# 1️⃣ Target to test

$Target = "google.com"

# 2️⃣ Timestamped output folder

$Timestamp = Get-Date -Format "yyyy-MM-dd_HH-mm-ss"

$OutputDir = "$env:USERPROFILE\Desktop\NetDiag_$Timestamp"

New-Item -ItemType Directory -Path $OutputDir | Out-Null

# 3️⃣ File paths

$PingFile     = "$OutputDir\ping.txt"

$TracertFile  = "$OutputDir\tracert.txt"

$PathpingFile = "$OutputDir\pathping.txt"

$IPConfigFile = "$OutputDir\ipconfig.txt"

# 4️⃣ Collect IP configuration

ipconfig /all > $IPConfigFile

# 5️⃣ Ping test (quick connectivity)

ping $Target -n 10 > $PingFile

# 6️⃣ Traceroute (path discovery)

tracert $Target > $TracertFile

# 7️⃣ Pathping (packet loss + latency per hop)

pathping $Target > $PathpingFile

# 8️⃣ Summary output

Write-Host "Network diagnostics completed." -ForegroundColor Green

Write-Host "Results saved to: $OutputDir"

🔬 What This Script Does (Step-by-Step)

1️⃣ Defines a target

• Can be a hostname (google.com) or IP (8.8.8.8)
  
  

• Replace with VPN gateway, internal server, or SaaS endpoint
  
  

2️⃣ Creates a timestamped folder

• Prevents overwriting previous diagnostics
  
  

• Ideal for ticket attachments
  
  

3️⃣ Captures ipconfig /all

• Verifies:
  
  

  • IP address
    
    

  • Subnet mask
    
    

  • Default gateway
    
    

  • DNS servers
    
    

• This alone resolves many “no internet” tickets
  
  

4️⃣ Runs ping

• Confirms basic reachability
  
  

• Detects total packet loss
  
  

5️⃣ Runs tracert

• Shows where latency starts
  
  

• Helps determine LAN vs ISP vs remote issue
  
  

6️⃣ Runs pathping

• Identifies packet loss per hop
  
  

• Essential for intermittent issues (VoIP, VPN, Teams)
  
  

🧠 How Helpdesk Uses the Output

🟢 Ping OK, Tracert slow, Pathping loss at hop 1
→ Local router / Wi-Fi issue

🟡 Loss starts at hop 2–3
→ ISP congestion

🔴 Loss only near destination
→ Remote service or VPN endpoint issue

This is escalation-grade evidence, not guesswork.

⌨️ Productivity & Automation Tips

⭐ Run PowerShell as Admin
Win + X → A

⭐ Bypass execution policy (temporary session):

Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass

⭐ Make it reusable:

• Save as NetDiag.ps1
  
  

• Right-click → Run with PowerShell
  
  

⭐ Advanced:

• Replace $Target with:
  
  

$Target = Read-Host "Enter hostname or IP"

📝 English Improvement (Micro-Correction)

Original idea:

“Try it out. Practice it yourself.”

Improved technical phrasing:

“Running these diagnostics in controlled scenarios builds pattern recognition for real-world troubleshooting.”

This version is more precise, neutral, and professional.

🔎 Interview Insight (Why This Matters)

When interviewers ask:

“How do you troubleshoot network issues?”

You can answer structurally:

• Verify IP configuration
  
  

• Confirm reachability
  
  

• Trace the route
  
  

• Measure packet loss per hop
  
  

That signals methodical thinking, not trial-and-error.

Would you like the same script adapted for VPN troubleshooting (split tunnel vs full tunnel) with automatic DNS comparison? Yes/No

yes

Below is a VPN-focused PowerShell diagnostic script designed to detect split-tunnel vs full-tunnel behavior, DNS leaks, gateway changes, and routing anomalies. This is exactly the level of structured reasoning interviewers and senior analysts look for.

🧪 PowerShell Script — VPN Diagnostics (Split vs Full Tunnel)

# ===========================

# VPN Diagnostic Script

# Focus: Split Tunnel vs Full Tunnel

# ===========================

$Timestamp = Get-Date -Format "yyyy-MM-dd_HH-mm-ss"

$OutputDir = "$env:USERPROFILE\Desktop\VPN_Diag_$Timestamp"

New-Item -ItemType Directory -Path $OutputDir | Out-Null

# Files

$IPConfigBefore = "$OutputDir\ipconfig_before.txt"

$IPConfigAfter  = "$OutputDir\ipconfig_after.txt"

$RouteTable     = "$OutputDir\route_print.txt"

$DNSResolve     = "$OutputDir\dns_test.txt"

$PublicIP       = "$OutputDir\public_ip.txt"

# Targets

$InternalTarget = "intranet.company.local"

$ExternalTarget = "google.com"

# 1️⃣ Capture state BEFORE VPN

ipconfig /all > $IPConfigBefore

route print > $RouteTable

# 2️⃣ External IP before VPN

nslookup myip.opendns.com resolver1.opendns.com > $PublicIP

Write-Host "Connect to VPN now, then press Enter"

Read-Host

# 3️⃣ Capture state AFTER VPN

ipconfig /all > $IPConfigAfter

# 4️⃣ DNS resolution test

nslookup $InternalTarget > $DNSResolve

nslookup $ExternalTarget >> $DNSResolve

Write-Host "VPN diagnostics completed."

Write-Host "Results saved to: $OutputDir"

🧠 How This Script Detects Tunnel Type

🔵 Full Tunnel VPN

✔ Default gateway changes to VPN adapter
✔ Public IP changes
✔ All traffic routed through corporate network
✔ DNS servers usually corporate

Evidence to look for:

• New 0.0.0.0 route via VPN
  
  

• Public IP belongs to company or cloud provider
  
  

• DNS = internal IPs
  
  

🟡 Split Tunnel VPN

✔ Default gateway remains local
✔ Only internal routes added
✔ Public IP unchanged
✔ External traffic goes directly to ISP

Evidence to look for:

• Route table shows specific subnets (10.x / 172.16.x / 192.168.x)
  
  

• Public IP remains ISP
  
  

• DNS may be mixed (risk of DNS leak)
  
  

🔍 What to Compare (Before vs After)

1️⃣ ipconfig /all

• DNS Servers
  
  

• Default Gateway
  
  

• VPN Adapter IP range
  
  

2️⃣ route print

• New static routes
  
  

• Default route changes
  
  

3️⃣ nslookup

• Internal host resolution
  
  

• External name resolution
  
  

🚨 Common Real-World Issues Detected

❌ VPN connected but internal sites fail
→ DNS mismatch

❌ Internet breaks after VPN connects
→ Full tunnel + no internet breakout

❌ Teams / Zoom drops on VPN
→ MTU or split tunnel misconfiguration

❌ Security alert
→ DNS leak (external DNS used while on VPN)

⌨️ Helpdesk Speed Tips

⭐ Open Network Adapters instantly
Win + R → ncpa.cpl

⭐ Reset stack if adapter corrupt:

netsh int ip reset

⭐ Flush DNS:

ipconfig /flushdns

⭐ Show only active routes:

Get-NetRoute | Where-Object {$_.State -eq "Active"}

📝 English Refinement (Interview-Ready)

Casual:

“I check if the VPN is working.”

Professional:

“I verify routing, DNS resolution, and gateway behavior to determine whether the VPN is operating in split-tunnel or full-tunnel mode.”

🧩 Why This Wins Interviews

You are:

• Thinking in network layers
  
  

• Collecting evidence
  
  

• Avoiding assumptions
  
  

• Speaking in verifiable signals
  
  

That’s analyst behavior, not script-monkey behavior.

Next logical step:
Would you like a decision tree (flowchart) you can memorize for VPN/network troubleshooting during interviews and real tickets? Yes/No

yes

Below is a mental decision tree you can reuse verbatim in interviews and daily helpdesk work. Think of it as a compressed troubleshooting algorithm: deterministic, calm, and evidence-driven.

🌐 Network & VPN Troubleshooting Decision Tree (Helpdesk → Analyst)

1️⃣ “Does the device have a valid IP configuration?”

⭐ Tools
• ipconfig /all
• ncpa.cpl

🔎 Check
• IP address not 169.254.x.x
• Subnet mask present
• Default gateway present
• DNS servers listed

❌ If invalid
→ DHCP failure / adapter issue
→ Disable–enable adapter or netsh int ip reset

2️⃣ “Can the device reach its local gateway?”

⭐ Tools
• ping <default-gateway>

🔎 Interpretation
• Success → local network OK
• Failure → Wi-Fi, cable, VLAN, or NIC issue

❌ If failure
→ Local network problem, stop here

3️⃣ “Can it reach the internet by IP?”

⭐ Tools
• ping 8.8.8.8

🔎 Interpretation
• Success → routing works
• Failure → gateway or ISP issue

❌ If failure
→ Router / ISP escalation

4️⃣ “Can it resolve DNS?”

⭐ Tools
• nslookup google.com

🔎 Interpretation
• Fails but IP ping works → DNS issue
• Works → proceed

❌ If DNS fails
→ Change DNS / flush cache / VPN DNS mismatch

5️⃣ “Where does the latency or failure start?”

⭐ Tools
• tracert google.com

🔎 Interpretation
• Delay at hop 1 → LAN
• Delay at hop 2–3 → ISP
• Delay near destination → remote service

6️⃣ “Is there packet loss, and where?”

⭐ Tools
• pathping google.com

🔎 Interpretation
• Loss at hop 1 → Wi-Fi/router
• Loss mid-path → ISP congestion
• Loss near target → remote endpoint

📌 This step explains intermittent issues

7️⃣ “Is a VPN involved?”

⭐ Tools
• ipconfig /all
• route print

🔎 Determine tunnel type

🟢 Full Tunnel
• Default gateway = VPN
• Public IP changes

🟡 Split Tunnel
• Default gateway unchanged
• Only internal routes added

8️⃣ “Can internal resources be resolved?”

⭐ Tools
• nslookup intranet.company.local

❌ If fails on VPN
→ DNS leak or missing internal DNS
→ Escalate to VPN/network team

🧠 One-Sentence Interview Answer (Memorizable)

“I verify IP configuration, confirm gateway reachability, test routing and DNS separately, then trace and measure packet loss per hop, adjusting for VPN routing behavior when present.”

That sentence alone places you above average candidates.

⌨️ Speed-Run Commands (Muscle Memory)

⭐ Network adapters
Win + R → ncpa.cpl

⭐ Full reset
Settings → Network Reset

⭐ DNS cleanup

ipconfig /flushdns

⭐ Routes only

route print

⭐ Active routes (PowerShell)

Get-NetRoute | Where-Object {$_.State -eq "Active"}

📝 English Precision Upgrade

Less precise:

“I try a few commands to see what’s wrong.”

Sharper:

“I isolate the failure layer by layer, validating configuration, routing, name resolution, and packet integrity.”

🧩 Why This Works Psychologically

• Reduces anxiety under pressure
• Prevents random guessing
• Creates confidence through structure
• Converts chaos into a finite checklist

This is exactly how senior analysts stay calm.

Next logical upgrade:
Would you like a printable one-page cheat sheet (PDF-style layout) you can memorize before interviews or keep beside you during tickets? Yes/No

yes

Below is a one-page, printable mental cheat sheet. You can read it top-to-bottom in under 30 seconds and recall it under pressure. This is optimized for helpdesk interviews, live troubleshooting, and anxiety-safe structure.

🧠 NETWORK & VPN TROUBLESHOOTING — ONE-PAGE CHEAT SHEET

⭐ GOAL
Identify where the failure occurs:
Device → LAN → Gateway → ISP → DNS → Route → VPN → Remote Service

1️⃣ IP CONFIGURATION (FOUNDATION)

🛠️ Command
ipconfig /all

🔎 Verify
• IP ≠ 169.254.x.x
• Subnet mask present
• Default gateway present
• DNS servers listed

❌ If broken
→ DHCP / adapter issue
→ ncpa.cpl → disable/enable
→ netsh int ip reset

2️⃣ LOCAL NETWORK

🛠️ Command
ping <default-gateway>

✅ Works → LAN OK
❌ Fails → Wi-Fi, cable, VLAN, NIC

🧠 Rule
If gateway fails, stop. Internet tests are meaningless.

3️⃣ INTERNET (ROUTING)

🛠️ Command
ping 8.8.8.8

✅ Works → Routing OK
❌ Fails → Router / ISP issue

4️⃣ DNS (NAME RESOLUTION)

🛠️ Command
nslookup google.com

🧠 Interpret
• IP ping works + DNS fails → DNS issue
• DNS works → proceed

🛠️ Fix
ipconfig /flushdns
Change DNS (8.8.8.8 / 1.1.1.1 for testing)

5️⃣ PATH & LATENCY

🛠️ Command
tracert google.com

🧠 Interpret
• Delay at hop 1 → LAN
• Delay at hop 2–3 → ISP
• Delay near end → remote service

6️⃣ PACKET LOSS (INTERMITTENT ISSUES)

🛠️ Command
pathping google.com

🧠 Interpret
• Loss at hop 1 → Wi-Fi / router
• Loss mid-path → ISP congestion
• Loss near target → remote endpoint

📌 Explains VPN drops, VoIP glitches, Teams freezes

7️⃣ VPN CHECK

🛠️ Commands
ipconfig /all
route print

🟢 Full Tunnel
• Default gateway = VPN
• Public IP changes

🟡 Split Tunnel
• Default gateway unchanged
• Only internal routes added

8️⃣ INTERNAL ACCESS (VPN)

🛠️ Command
nslookup intranet.company.local

❌ Fails on VPN
→ DNS leak / missing internal DNS
→ Escalate to network/VPN team

🎯 INTERVIEW-READY ONE-LINER (MEMORIZE)

“I validate IP configuration, confirm gateway reachability, test routing and DNS independently, then trace latency and packet loss per hop, accounting for VPN routing behavior.”

⌨️ SPEED COMMANDS (MUSCLE MEMORY)

⭐ Network adapters
Win + R → ncpa.cpl

⭐ Full network reset
Settings → Network Reset

⭐ Routes
route print

⭐ Active routes only

Get-NetRoute | Where-Object {$_.State -eq "Active"}

🧠 CALM RULE (IMPORTANT)

Never jump steps.
Each test proves or disproves a layer.
Structure beats intuition when stress is high.

✍️ ENGLISH PRECISION UPGRADE

Casual:
“I tried a few things and it worked.”

Professional:
“I isolated the failure to DNS resolution after confirming routing and gateway connectivity.”

This page alone is enough to outperform most Level-1 candidates because it shows method, not memorization.

Would you like this converted into a PDF-style layout or a French version for bilingual interviews? Yes/No

yes

Perfect. Below are both deliverables in one response:

1️⃣ PDF-style layout (English, print-ready)
2️⃣ French version (for bilingual interviews in Québec / Canada)

No filler, no ambiguity, same structure in both languages so your brain doesn’t context-switch under stress.

📄 NETWORK & VPN TROUBLESHOOTING

ONE-PAGE CHEAT SHEET (PDF-STYLE — ENGLISH)

🎯 OBJECTIVE

Locate the failure point, layer by layer:
Device → LAN → Gateway → ISP → DNS → Route → VPN → Remote Service

1️⃣ IP CONFIGURATION

Command
ipconfig /all

Verify
• Valid IP (not 169.254.x.x)
• Subnet mask
• Default gateway
• DNS servers

If broken
→ DHCP or adapter issue
→ ncpa.cpl → disable / enable
→ netsh int ip reset

2️⃣ LOCAL NETWORK

Command
ping <default-gateway>

Result
• Success → LAN OK
• Failure → Wi-Fi, cable, VLAN, NIC

Rule
If gateway fails, stop. Do not test internet yet.

3️⃣ INTERNET ROUTING

Command
ping 8.8.8.8

Result
• Success → Routing OK
• Failure → Router or ISP issue

4️⃣ DNS RESOLUTION

Command
nslookup google.com

Interpretation
• IP ping works + DNS fails → DNS issue
• DNS works → continue

Fix
ipconfig /flushdns
Test alternate DNS (8.8.8.8 / 1.1.1.1)

5️⃣ ROUTE & LATENCY

Command
tracert google.com

Interpretation
• Hop 1 delay → LAN
• Hop 2–3 delay → ISP
• End delay → remote service

6️⃣ PACKET LOSS (INTERMITTENT ISSUES)

Command
pathping google.com

Interpretation
• Loss at hop 1 → Wi-Fi/router
• Mid-path loss → ISP congestion
• End loss → remote endpoint

7️⃣ VPN CHECK

Commands
ipconfig /all
route print

Full Tunnel
• Default gateway = VPN
• Public IP changes

Split Tunnel
• Default gateway unchanged
• Only internal routes added

8️⃣ INTERNAL ACCESS (VPN)

Command
nslookup intranet.company.local

Failure
→ DNS leak or missing internal DNS
→ Escalate to network team

🗣️ INTERVIEW SENTENCE (MEMORIZE)

“I validate IP configuration, confirm gateway reachability, test routing and DNS independently, then trace latency and packet loss per hop, accounting for VPN routing behavior.”

📄 DÉPANNAGE RÉSEAU & VPN

FICHE MÉMO — VERSION FRANÇAISE (ENTREVUES BILINGUES)

🎯 OBJECTIF

Identifier précisément où la panne se produit :
Poste → Réseau local → Passerelle → FAI → DNS → Routage → VPN → Service distant

1️⃣ CONFIGURATION IP

Commande
ipconfig /all

Vérifier
• Adresse IP valide (≠ 169.254.x.x)
• Masque de sous-réseau
• Passerelle par défaut
• Serveurs DNS

Si invalide
→ Problème DHCP ou carte réseau
→ ncpa.cpl → désactiver / réactiver
→ netsh int ip reset

2️⃣ RÉSEAU LOCAL

Commande
ping <passerelle>

Résultat
• Succès → LAN fonctionnel
• Échec → Wi-Fi, câble, VLAN, carte réseau

Règle
Si la passerelle ne répond pas, on s’arrête ici.

3️⃣ ACCÈS INTERNET

Commande
ping 8.8.8.8

Résultat
• Succès → Routage OK
• Échec → Routeur ou FAI

4️⃣ RÉSOLUTION DNS

Commande
nslookup google.com

Interprétation
• Ping IP OK + DNS KO → Problème DNS
• DNS OK → Continuer

Correction
ipconfig /flushdns
Tester DNS public (8.8.8.8 / 1.1.1.1)

5️⃣ CHEMIN & LATENCE

Commande
tracert google.com

Analyse
• Lenteur au 1er saut → Réseau local
• 2e–3e saut → FAI
• Fin du tracé → Service distant

6️⃣ PERTE DE PAQUETS

Commande
pathping google.com

Analyse
• Perte au 1er saut → Wi-Fi / routeur
• Perte intermédiaire → Congestion FAI
• Perte finale → Service distant

7️⃣ VPN

Commandes
ipconfig /all
route print

Tunnel complet
• Passerelle = VPN
• IP publique change

Tunnel fractionné
• Passerelle locale conservée
• Routes internes seulement

8️⃣ ACCÈS INTERNE (VPN)

Commande
nslookup intranet.entreprise.local

Échec
→ Problème DNS interne / fuite DNS
→ Escalade équipe réseau

🗣️ PHRASE D’ENTREVUE

« Je valide la configuration IP, la passerelle, le routage et le DNS séparément, puis j’analyse la latence et la perte de paquets en tenant compte du mode VPN. »

🧠 FINAL NOTE (IMPORTANT)

This structure works because it removes improvisation.
Each command proves a layer.
That’s how senior analysts think under pressure.