My DNS Troubleshooting Workflow

Half the "network is down" tickets I've seen were actually DNS problems. The other half were misconfigured firewalls. Here's how I quickly figure out which is which.

Step 1: Ping an IP Address

ping 8.8.8.8

This bypasses DNS entirely. If this works, your network is fine - the problem is name resolution. If this fails, don't waste time on DNS yet.

No response? Check:

Is your WiFi/Ethernet connected?
Can you ping your gateway? (ping 192.168.1.1)
Is there a firewall blocking outbound traffic?

Step 2: Ping a Hostname

ping google.com

IP works, hostname fails = DNS problem. Continue with DNS troubleshooting.

Both work = intermittent issue or specific to one site. Try the specific domain that's failing.

Step 3: Check Your DNS Servers

Linux:

cat /etc/resolv.conf
# or for systemd-resolved
resolvectl status

macOS:

networksetup -getdnsservers Wi-Fi

Windows:

ipconfig /all

Look at which DNS servers are configured. Are they reachable? Sometimes DHCP assigns a broken or slow DNS server.

Step 4: Test with a Known-Good DNS

nslookup google.com 8.8.8.8

This queries Google's DNS directly. If this works but your configured DNS doesn't, you've found the problem.

Linux/macOS with dig:

dig @8.8.8.8 google.com

I prefer dig - it shows more detail including TTLs and record types.

Step 5: Flush DNS Cache

Stale cache causes weird issues. A domain moved IPs but your machine still has the old one cached.

Windows:

ipconfig /flushdns

macOS:

sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder

Linux (systemd):

sudo systemd-resolve --flush-caches

Switching to Public DNS

If your ISP's DNS is the problem, switch to public resolvers:

Cloudflare: 1.1.1.1, 1.0.0.1 Google: 8.8.8.8, 8.8.4.4 Quad9: 9.9.9.9

Linux quick fix:

echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

Note: NetworkManager or systemd-resolved might overwrite this. For permanent changes, configure through your network manager.

Windows: Control Panel → Network → Adapter Properties → IPv4 → Use the following DNS server addresses

When It's Not DNS

If DNS lookups work but the site still doesn't load:

Check if it's blocked:

curl -I https://example.com

Check the route:

traceroute example.com   # Linux/macOS
tracert example.com      # Windows

Check if the service is running:

nc -zv example.com 443

Common Patterns I've Seen

"Internet is slow" - Often DNS. Slow resolver = delay before every connection starts.

"Only some sites work" - Either DNS (try different resolver) or routing/firewall.

"Worked yesterday, broken today" - DNS cache with expired record, or the site changed IPs and propagation hasn't reached you.

"WiFi works, Ethernet doesn't" - Different DHCP servers assigning different DNS. Check configs on both.

Key Takeaways

Always ping IP (8.8.8.8) first - this separates network from DNS issues
Use nslookup or dig to test specific DNS servers
Public DNS (1.1.1.1, 8.8.8.8) is reliable fallback for testing
Flush DNS cache when domains recently changed
Slow internet is often slow DNS - try a faster resolver