Question

Difficulty: MediumWired and Wireless Network Issues

A desktop workstation in an office environment fails to connect to network resources after a desk rearrangement. A technician decides to troubleshoot the issue using a bottom-up approach following the OSI model layers. In what order should the technician perform the following diagnostic steps, starting from Layer 1 (Physical) up through Layer 3 (Network)?

  1. 1Inspect the Ethernet cable connections and check for link light activity on the network interface card (NIC).
  2. 2Verify the switch port status and confirm that MAC address learning and port VLAN assignments are configured correctly.
  3. 3Run `ipconfig /all` to verify local host IP address assignment, subnet mask, and DHCP server configuration.
  4. 4Execute a `ping` command to the default gateway address to test local ICMP reachability across subnets.

Answer

The correct sequence starts with checking physical cable connections and link lights (Layer 1), followed by verifying switch port settings and MAC/VLAN configurations (Layer 2), inspecting the local host's IP address assignment via `ipconfig` (Layer 3 configuration), and finally testing IP reachability to the gateway using `ping` (Layer 3 communication).
A bottom-up troubleshooting methodology starts at the Physical Layer (Layer 1), verifying cable connections and link lights. It then moves to the Data Link Layer (Layer 2) to check switch port status and VLAN configuration, followed by the Network Layer (Layer 3) to inspect host IP addressing (`ipconfig /all`) and test end-to-end ICMP connectivity (`ping`).

Step-by-Step Solution

1
Check physical layer components (Layer 1).
Confirm Ethernet cable is securely connected and NIC link LEDs illuminate.
Troubleshooting bottom-up requires ensuring physical media and signaling are operational before checking logical configurations.
2
Verify data link layer components (Layer 2).
Check switch port LEDs and VLAN assignment.
Layer 2 framing and VLAN tagging must function properly for frames to reach network services.
3
Inspect local network layer configuration (Layer 3).
Determine if a valid DHCP IP address or an APIPA (169.254.x.x169.254.x.x) address is assigned.
Valid IP addressing is required for host communication beyond the physical/data link layer.
4
Test network layer reachability (Layer 3).
Verify ICMP echo responses from the default gateway.
Pinging the gateway tests active IP routing and confirms packets can leave the local subnet.

Key Concept

Bottom-up troubleshooting methodology follows the OSI model from Physical Layer (Layer 1) to Data Link Layer (Layer 2) and Network Layer (Layer 3).
Estimated Time:1m 30s
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