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Difficulty: MediumWired and Wireless Network Issues

A network technician is dispatched to troubleshoot a workstation that suddenly lost all network connectivity after an office redesign. Following the standard CompTIA bottom-up (Layer 1 through Layer 7) network troubleshooting methodology, in what sequence should the technician perform the diagnostic actions below?

  1. 1Inspect the physical RJ-45 patch cable connections and verify that status link lights on the network interface card (NIC) are lit.
  2. 2Execute ipconfig /all to check the adapter configuration and determine if an APIPA address (169.254.x.x) is assigned.
  3. 3Ping the IPv4 loopback address (127.0.0.1) to confirm the local TCP/IP protocol stack is operating correctly.
  4. 4Ping the local default gateway address to verify connectivity across the local subnet to the router.
  5. 5Run nslookup to query a domain name and confirm remote DNS hostname resolution is functioning.

Answer

The proper bottom-up diagnostic sequence begins with verifying physical link lights and cables (Layer 1), checking local IP configuration with ipconfig (Layer 2/3), testing the loopback address (127.0.0.1) for stack integrity, pinging the default gateway for subnet connectivity, and finally testing DNS domain name resolution with nslookup.
Following the standard CompTIA bottom-up troubleshooting methodology, technicians work sequentially from Layer 1 up to Layer 7. The process starts by checking cables and link lights (Physical), reviewing local adapter configuration with ipconfig, verifying the internal TCP/IP stack with loopback ping (127.0.0.1), testing subnet routing by pinging the default gateway, and lastly verifying higher-layer services like DNS hostname resolution with nslookup.

Step-by-Step Solution

1
Verify Layer 1 Physical Layer connectivity
Ensure patch cable is connected securely and physical link lights are lit on both the host NIC and wall jack.
Troubleshooting higher layers is ineffective if physical connectivity is broken.
2
Inspect local IP configuration using ipconfig /all
Determine if the host has a valid DHCP configuration, static IP, or an APIPA address.
Identifies whether the NIC has established a link and communicated with local network services.
3
Test local TCP/IP protocol stack using ping 127.0.0.1
Verify that the local operating system protocol drivers are installed and processing packets.
Confirms the host software stack can send and receive ICMP traffic internally.
4
Test local subnet network pathway by pinging the default gateway
Confirm connectivity between the local workstation and the subnet router interface.
Validates that frames and packets travel across the local network segment successfully.
5
Test Application/Name Resolution services using nslookup
Confirm DNS servers resolve human-readable domain names to destination IP addresses.
Verifies end-to-end high-level application functionality and name resolution services.

Key Concept

OSI Model Bottom-Up Network Troubleshooting
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Topics

Wired and Wireless Network Issues

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