Everyday Internet & Troubleshooting
What Is a DNS Cache, and How Do You Flush It?
To avoid looking up the same names over and over, your device keeps a DNS cache. Usually it helps — occasionally it needs clearing.
Why a cache exists
Every time you visit a site, your device asks DNS to turn its name into an IP address. Doing that fresh every time would be wasteful, so your device (and your resolver) keep a DNS cache — a short-term memory of recent lookups. Repeat visits then skip the lookup entirely, making browsing faster.
Time to live
Each cached record has a time to live (TTL) that says how long it may be kept. When the TTL expires, the record is discarded and the next lookup fetches a fresh answer. TTLs are why changes to a domain's settings don't take effect everywhere instantly — old answers linger until they age out.
When to flush
Occasionally the cache holds a stale or wrong answer — for instance, right after a website moves to a new server, or when a lookup fails and the failure gets cached. Flushing the DNS cache forces your device to forget everything and look up fresh answers.
How to flush it
- Windows: run
ipconfig /flushdnsin Command Prompt. - macOS: run
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponderin Terminal. - Linux: the command depends on your resolver (for example,
sudo resolvectl flush-caches). - Browsers keep their own DNS cache too, which restarting the browser clears.
A common fix
"Flush your DNS" is a standard troubleshooting step when a site won't load correctly but works elsewhere, or right after DNS changes. It's harmless — the cache simply rebuilds itself as you browse. If flushing doesn't help, the issue is likely elsewhere, and tools like ping and traceroute are the next step.