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copied!<p>DNS caching occurs at multiple levels: Application asks local system, which asks locally configured resolving DNS server, which asks authoritative DNS servers.</p> <h3>Caching by Application varies.</h3> <ul> <li>I've found for Firefox that quitting and restarting works. The relevant settings in <code>about:config</code> are <code>network.dnsCacheEntries</code> and <code>network.dnsCacheExpiration</code>, which can be set to <code>0</code> in order to disable caching.</li> </ul> <h3>Caching by local system is typically 1 hour.</h3> <ul> <li>Diagnostic: ping, like other applications, uses local system DNS cache</li> <li>Flush MacOsX 10.8: <code>sudo killall -HUP mDNSResponder</code> <a href="http://support.apple.com/kb/HT5343" rel="noreferrer">(reference)</a><br> (May vary for other versions)</li> <li>Flush Windows: <code>ipconfig /flushdns</code> (only if the DNS caching service, <code>HKLM\SYSTEM\CurrentControlSet\Services\Dnscache</code>, is enabled; check with <code>net start|findstr /i dns</code> or <code>compmgmt.msc</code>)</li> <li>Linux/Unix may use <code>nscd</code> (name services caching daemon), or <code>dnsmasq</code>, or both ...</li> </ul> <h3>Caching by local resolving DNS server may run to several days, depending on TTL associated with DNS record.</h3> <ul> <li>Diagnostic: <code>nslookup</code> first reports address of resolving server, then address requested.</li> <li>Flush BIND: <code>rndc flush</code> <em>or</em> <code>rndc flushname DOMAIN.NAME</code></li> </ul> <p><strong>TTL</strong> stands for "time to live" a term used to describe how long a DNS record is to be deemed valid by the requesting client or server. A short TTL means that the requester is told not to cache a DNS lookup for too long. The TTL can range from mere seconds (e.g. for DynDNS and similar) to days or weeks.</p>

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