Unit 9 · Network Troubleshooting

9.4The "cannot reach the Internet" sequence

This PCDefault gatewayInternetDNS server1 ping 127.0.0.12 ipconfig /all3 ping gateway4 ping 8.8.8.85 ping www.google.comname works too?6 tracert 8.8.8.8: where does the path stop?
The standard sequence works outwards from your own computer, so the first test that fails shows where the fault is
  1. ping 127.0.0.1 - is the TCP/IP software working on this computer?
  2. ipconfig /all - is the IP address valid (not 169.254.x.x)? Is the gateway correct?
  3. ping the default gateway - is the local network working?
  4. ping 8.8.8.8 - is the Internet reachable by IP?
  5. ping www.google.com - does DNS work? If this fails while step 4 works, the fault is DNS.
  6. tracert 8.8.8.8 - where does the path stop?

Write the evidence

At each step record the command and the result (ping 192.168.1.1 → destination host unreachable). That log becomes your theory test and your ticket notes. Guessing without recording leads to looping through the same checks.

"Cannot reach the Internet" decision path

  1. Can you ping 127.0.0.1? No → OS/network stack problem.
  2. Do you have an IP address? 169.254.x.x → DHCP failed. No address → NIC/driver/disabled interface.
  3. Ping the default gateway. Fail → wrong VLAN/cable/gateway IP or gateway down.
  4. Ping a public IP (for example 1.1.1.1). Fail → routing/NAT/ISP/firewall outbound issue.
  5. Ping a name (ping www.google.com) or use nslookup. Fail while IP works → DNS problem.
  6. Browser still fails while ping works → proxy settings, firewall port 80/443, or application issue.

Write down which step first failed; that is your theory for 9.1.

Remember

  • Local → gateway → public IP → name → application.
  • APIPA means DHCP trouble; names failing alone means DNS trouble.