Specific sites fail to load while everything else works fine? That's classic DNS — the name lookup is failing for those specific sites.

What DNS does

When you visit example.com, your laptop asks a DNS server to translate the name to an IP. If that fails, the page doesn't load. The rest of the internet works because it uses cached lookups.

1. Flush DNS cache

The cache holds bad answers as long as good ones. Clear it:

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macOS:<br>[unrendered]

Try the failing site again.

2. Verify with ping vs. nslookup

Open Command Prompt or Terminal and:

ping example.com
  • If you get an IP back and replies: DNS is working, the issue is somewhere else (firewall, certificate, blocked site)
  • If "could not resolve host": DNS is broken
  • If you get an IP but no responses: DNS works but the site is blocked or down

For more detail:

nslookup example.com

Shows which DNS server answered, what IP it returned.

3. Change DNS servers

Your default DNS server is usually your office router or ISP. If it's having issues, switch to public DNS:

  • Cloudflare: 1.1.1.1 (primary) and 1.0.0.1 (secondary)
  • Google: 8.8.8.8 and 8.8.4.4
  • Quad9: 9.9.9.9 (with malware filtering)

Windows

Settings → Network → Wi-Fi → click your network → IP assignment → DNS server assignment → Edit → Manual → set IPv4 to 1.1.1.1, alternate to 8.8.8.8.

macOS

System Settings → Network → Wi-Fi → Details → DNS → click + and add the IPs.

After changing, flush DNS again.

4. Hosts file override

Some sites refuse to load because the hosts file maps them somewhere else. Open:

  • Windows: C:\Windows\System32\drivers\etc\hosts (open Notepad as admin)
  • macOS: /etc/hosts (Terminal: sudo nano /etc/hosts)

Look for the failing site. If you see entries like 127.0.0.1 example.com, those override DNS. Remove or comment with #.

5. Browser DNS-over-HTTPS

Chrome and Firefox can do their own DNS, bypassing your system. If your browser fails but ping works, the browser's DNS is broken:

  • Chrome: chrome://settings/security → Use secure DNS → toggle off, test, then back on with Cloudflare
  • Firefox: about:preferences#privacy → Enable DNS over HTTPS → adjust

6. VPN and DNS

When you connect to VPN, the VPN often replaces your DNS server with the company's. If you've just disconnected VPN and DNS still seems broken, the old DNS may be cached. ipconfig /flushdns again.

7. Slow DNS = slow page loads

If DNS resolves but slowly, every site feels sluggish. Switching to a faster DNS provider (Cloudflare is the fastest public option in most regions) often makes browsing feel snappier even without other changes.

When to ticket

Raise a ticket if:

  • Specific internal sites (intranet, ticketing, payroll) fail but external sites work — that's an internal DNS issue
  • DNS changes don't help
  • Multiple users on the same network can't reach a specific site

Include the failing URL, what nslookup <site> returns, and which DNS server you're using.