Diagram showing DNS cache being cleared and refreshed from DNS server

Domain Management

What Does Flushing DNS Do? A Plain-English Explanation

Domain 360 Team

·July 11, 2026·5 min read

Flush your DNS is the internet's most repeated troubleshooting tip and least explained one. Here is what it actually does and — more importantly — when it will and will not fix your problem.

Quick answer: Everyone says "flush your DNS" as a first fix, but very few people explain what it actually does. Here is the plain-English answer — and more importantly, when it will and will not solve your problem.

What Is the DNS Cache?

Every website visit starts with a DNS lookup: translating a domain name into an IP address. Your device stores recent results locally — this is the DNS cache. The stored entry has a TTL (Time to Live) set by the domain owner, usually 1-24 hours. Until it expires, your device uses the stored result without re-querying the DNS server.

This is efficient and correct — until DNS records change before the cache expires.

What Does Flush DNS Do?

Flushing DNS deletes the entire local cache immediately, regardless of individual TTL values. Every subsequent domain lookup fetches fresh data from the DNS server — whatever the server currently says.

Delete stored answers. Fetch new ones. That is the complete mechanism.

When Does Flushing DNS Actually Fix the Problem?

After a DNS change. A website moved to a new server. DNS records were updated. But your cached records still point to the old server. Flushing forces your device to fetch updated records.

After a domain is renewed. During a brief expiry window, DNS may have returned errors. After renewal and DNS restoration, flushing clears the error from cache.

DNS_PROBE_FINISHED_NXDOMAIN errors. Your device may have cached a negative response from when a domain was temporarily unreachable. Flushing clears the cached failure and forces a fresh lookup.

After changing DNS server. Switching from your ISP DNS to Cloudflare 1.1.1.1? Flush immediately ensures you query the new server for everything.

When Will Flushing DNS Not Fix the Problem?

Domain has expired. Flushing makes your device ask the DNS server for fresh data — but if the domain has expired and its records are removed, the fresh lookup returns the same error. Check domain expiry via WHOIS before spending time troubleshooting cache.

what does dns flush do for propagation delays? DNS changes take up to 48 hours to spread across all resolvers. Flushing your local cache just fetches a fresh copy of what the server currently has, which may still be the old record.

Only one browser is affected. Chrome, Firefox, and Edge all maintain internal DNS caches separate from the operating system. Flush Chrome DNS at chrome://net-internals/#dns.

The server is actually down. Flushing DNS finds the correct server — but if that server is offline, you still cannot reach the site.

what does a dns flush do for speed?

It does not improve internet download or upload speeds. DNS lookup time affects how quickly your browser starts loading each new website — typically 20-120 milliseconds. Flushing removes cached results, meaning the next visit to each previously visited website is fractionally slower until the cache rebuilds.

Speed improvements come from switching to a faster DNS server, not from flushing. Cloudflare DNS setup guide covers switching to 1.1.1.1.

What Are the Commands?

Windows: ipconfig /flushdns (in Command Prompt as administrator) Mac: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder Linux (systemd-resolved): sudo systemd-resolve --flush-caches

Full step-by-step guide for each platform: how to flush DNS.

How Often Should You Flush?

Only when you have a specific reason. Your OS manages cache expiry automatically using TTL values. Manual flushing only helps when cached data is specifically the problem — it is troubleshooting, not maintenance.

Quick Answers

What does flushing DNS actually do?

It deletes your device local store of recent DNS lookup results — the table that maps domain names to IP addresses. After flushing, your device must fetch DNS records fresh from the DNS server for every domain, rather than using stored results. This ensures you get the most current records.

Is flushing DNS safe?

Yes, completely. Flushing DNS removes temporary data that your device recreates automatically on the next DNS lookup. It does not affect your files, settings, browser history, passwords, or any application data. The only brief effect is that the next visit to any website takes a tiny fraction of a second longer while fresh DNS records are fetched.

Does flushing DNS speed up internet?

Not meaningfully. DNS lookups take milliseconds, and caching already makes repeated visits faster. Flushing DNS does not improve download speeds, ping, or overall connection performance. If your internet is slow, the cause is elsewhere — your ISP, router, or server capacity.

What problems does flushing DNS fix?

Flushing DNS specifically fixes problems caused by stale cached records: a website showing an old version after moving servers, DNS_PROBE_FINISHED_NXDOMAIN errors for working sites, and connection problems immediately after changing your DNS server settings.

Does flushing DNS log you out of websites?

No. DNS records and website login sessions are completely unrelated. Flushing DNS only affects which IP address your device uses to reach a domain — it does not touch cookies, session tokens, or any browser authentication data.

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