T2 DNS Failure Troubleshooting

Infrastructure Labs

T2 DNS Failure Troubleshooting

Technician Support

Project Overview

Simulated a DNS resolution failure for a standard user in a controlled environment. Conducted a full Tier-2 troubleshooting workflow, systematically ruling out common causes before identifying and resolving the root cause: incorrect DNS server assignment.

Scenario / Context

User type: Standard (non-admin) account
Operating system: Windows 10 / 11
Issue observed: User unable to access websites by domain name, but IP connectivity remained intact
Impact: Limited to the affected user account; other users not affected

Symptoms

Browser unable to load websites
ping domain.com fails
ping 8.8.8.8 succeeds
Applications relying on DNS fail

Hypotheses / Possible Causes

Now, there are multiple causes for these symptoms, such as a misconfigured hosts file, an incorrect DNS server assignment, the DNS Client service being stopped, a firewall blocking DNS traffic a corrupted DNS cache, or IPv6 misconfiguration.

Investigation / Actions taken

Each possibility was systematically tested:

Hosts file misconfiguration: The hosts file was checked and confirmed clean (Checked: C:\Windows\System32\drivers\etc\hosts in Notepad as Admin)
Incorrect DNS server assignment: The DNS server settings were reviewed, revealing the misassigned DNS (0.0.0.0 / 1.1.1.1), which ultimately was the root cause (Checked: ipconfig /all in Command Prompt)
DNS Client service stopped: The DNS Client service was running normally (Checked: services.msc and sc query dnscache)
Firewall blocking DNS traffic: Verified the firewall was not blocking DNS (Checked: netsh advfirewall firewall show rule name=all)
DNS cache corruption: The DNS cache was inspected and found clear (Checked: ipconfig /displaydns)
IPv6 misconfiguration: IPv6 settings were reviewed and appeared correct (Checked: ipconfig /all)