DNS problems can originate at three different layers — the client device, the local router, or the upstream DNS server — and the fastest diagnosis works outward from the client step by step rather than guessing.
Common Symptoms
- Some domains resolve, others don’t
- Direct IP access works but domain names fail
- Resolution is slow but eventually succeeds
Possible Causes
- Client-side DNS cache holding a stale/incorrect record
- Router’s DNS forwarding misconfigured
- Upstream DNS provider experiencing an outage
- A domain’s own DNS records misconfigured (not fixable on your end)
Before You Begin
Test the same domain from a device on a completely different network (e.g. mobile data instead of Wi-Fi) — if it fails there too, the problem is with the domain’s own DNS, not your network.
Method 1 — Test resolution directly, bypassing cache
Run nslookup against a specific server
Use the command below to query a public DNS server directly, bypassing any local cache or router-level forwarding.
Method 2 — Flush the local DNS cache
Clear cached records
On Windows, run ipconfig /flushdns; on macOS, use sudo dscacheutil -flushcache; then retest.
Method 3 — Test with a different DNS provider
Switch DNS servers temporarily
Manually set the device or router to use 1.1.1.1 or 8.8.8.8 and see if the problem disappears — if it does, the original DNS provider was the cause.
Useful Commands
nslookup example.com 8.8.8.8Frequently Asked Questions
Why does one website fail while everything else works?
This pattern usually points to a problem with that specific domain’s own DNS configuration (on the website owner’s end) rather than your network — test it from a different network to confirm.
Conclusion
Working outward — device cache, then router, then upstream provider, then the domain’s own DNS — isolates the actual failure point in a few minutes instead of guessing at fixes.
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