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Network troubleshooting for help desk

Use this when: a user says "the internet is down" and you need to find where it breaks, fix the common causes, or escalate with proof.

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IT-04 Network troubleshooting for help desk cheat sheet. Every table on it is repeated as text below.
Tap the sheet for the full-size image. The text version below is screen-reader friendly.

Text version

Everything on the sheet, as plain HTML: handy for screen readers, copy-paste and search.

Work up the stack: stop at the first failure

The examples use 192.0.2.1 as the gateway.

  1. Link: cable lights on? Wi-Fi on? Airplane mode off?
  2. IP address: ipconfig /all. A 169.254.x.x address means no DHCP reply.
  3. Gateway: ping 192.0.2.1. Is the local network OK?
  4. Internet: ping a public IP address your team trusts.
  5. DNS: nslookup example.com. Does the name resolve?
  6. App or port: Test-NetConnection example.com -Port 443. Is the port open?

Symptom to likely cause

SymptomLikely cause and next step
169.254.x.x addressNo DHCP reply: cable, wrong VLAN or DHCP server down. Try ipconfig /renew.
IP works, names failDNS: wrong DNS server or a bad cache. Run ipconfig /flushdns and check DNS in ipconfig /all.
"Connected, no internet"Gateway or DNS problem. Ping the gateway, then a public IP.
One site failsThat site, a proxy or a web filter. Try another browser and Test-NetConnection.
IP conflict warningTwo devices with one IP, often a static one. arp -a shows the MAC behind it.
Slow or drops on Wi-FiWeak signal or a crowded 2.4 GHz band. netsh wlan show interfaces shows the signal %.
Whole office downNot this PC. Check the switch, ISP or outage page, then escalate.

Diagnose (Windows)

CommandShows
Get-NetIPConfigurationIP, gateway and DNS
Resolve-DnsName example.comDNS answer
Test-NetConnection example.com -Port 443Is the port open?
ping -t 192.0.2.1Watch for drops (Ctrl+C to stop)
pathping example.comPacket loss per hop
tracert example.comWhere the path stops
netsh wlan show wlanreportWi-Fi history report

Wi-Fi checks

  • Signal: low signal %? Move closer.
  • Band: try 5 GHz if 2.4 GHz is crowded.
  • Profile: forget the network and rejoin.
  • Driver: update it and check power saving.
  • Captive portal: on guest Wi-Fi, open a browser.

Fix ladder

Run these in an admin prompt, in this order (Microsoft's recommended sequence):

  1. netsh winsock reset
  2. netsh int ip reset
  3. ipconfig /release, then ipconfig /renew
  4. ipconfig /flushdns
  5. Last resort: Settings, Network reset (the PC restarts)

Escalate with proof

  • User, PC name and location
  • Wired or Wi-Fi
  • ipconfig /all output
  • Which step failed
  • When it started
  • How many users are affected

Danger. Never turn off the firewall or antivirus "to test" the connection.

Caution. ipconfig /release drops a remote session. Network reset removes VPN clients and virtual switches.

Remember

  • 169.254 = DHCP never answered
  • IP works but names fail = DNS
  • Many users down = not the PC

Sources

Go deeper on the blog