Thread: DNS Caching???

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    DNS Caching???


    Say I have the domain xyz.com and I host it's name servers which are ns1/ns2.nameserver.com which currently say in the zone records that it belongs to ip 1.1.1.1. Now if I where to change that to 1.1.1.2 would that be instantanious OR would that need to propagate over the internet as well like when changing DNS server information on the whois data of that domain?
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    Re: DNS Caching???


    Originally posted by eliteboo
    Now if I where to change that to 1.1.1.2 would that be instantanious OR would that need to propagate over the internet as well like when changing DNS server information on the whois data of that domain?
    It all has to do with the caching of DNS information. Here's the deal. Let's say someone else tried to visit your site, just before you updated your nameserver information. Their caching nameserver will ask your nameserver for the DNS information and will receive 1.1.1.1. Now, their caching nameserver will cache the information for a while (determined largely by the time to live value specified in your zone records). So, the next few times that the person tries to visit your site, their caching nameserver will not bother to query your nameserver again and will instead return the cached information (1.1.1.1) for a while. Anyone else who uses the same caching nameserver will receive the cached information also. The cached information will not be refreshed until the time-to-live runs out. So, even if you change your zone record, the caching nameserver will not query your nameserver for a while.

    However, let's say you just changed your zone information and someone else, whose caching nameserver did not have your old information cached, tries to visit your site. Their nameserver will query your nameserver and therefore receive 1.1.1.2 and cache the info and so on. What this means is that users of the first caching nameserver will have 1.1.1.1 for a while, whereas users of the second caching nameserver will have 1.1.1.2. This means that you'll receive hits on both IP addresses for a while, until the nameservers that had your old DNS information cached have a chance to refresh.
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