The failure of a ping to 127.0.0.1 (the loopback address) indicates a problem with the workstation's TCP/IP stack or network interface card (NIC). Since 127.0.0.1 is a local address, the issue is not related to the network, router, or DNS. The first step in diagnosing this issue is to verify the NIC interface status to ensure the network adapter is functioning and properly configured.
Why not Verify the network is not congested? Network congestion affects external connectivity, not the loopback address.
Why not Verify the router is not dropping packets? Router issues are irrelevant since the loopback ping fails locally.
Why not Verify that DNS is resolving correctly? DNS resolution is not involved in pinging 127.0.0.1, which uses a direct IP address.
Reference:CompTIA Network+ N10-009 Objective 5.2: Explain the troubleshooting methodology. The CompTIA Network+ Study Guide (e.g., Chapter 13: Network Troubleshooting) emphasizes that a failed loopback ping indicates a local TCP/IP stack or NIC issue, and checking the NIC status is the first diagnostic step.