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I have set up a DNS server in my home, will I have to wait for the isp to refresh there cache before DNS is active?

Some website I have found says this is called "DNS propagation time" and how long could this take?

user9517
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Jonathan
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2 Answers2

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This is dependent on whether your DNS server is actually taking over any actual DNS configuration for your Internet Domain - e.g. NS entry/function. If your DNS server is just a free-standing internal server and no actual Internet DNS entries/updates are required, then no impact.

If is it taking the place of or being placed in as an additional NS for an active Internet DNS domain configuration, then it will require some time for the entry from where the actual Internet DNS server was made to propagate/update to the rest of the Internet DNS servers. This used to take around 72 hours in the past, but may now be as quick as completing within 24 hours.

user48838
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  • Thank you for your help, I can only connect via domain only on the domain server and out side our network only by the i.p at the moment so I *think* it should work – Jonathan Jun 19 '11 at 10:04
  • It sounds like you have setup an internal DNS server at this point, so no DNS propagation is involved across the Internet. – user48838 Jun 19 '11 at 10:07
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It depends.

  • If you aren't even running a content DNS server at all, then there's nothing to cache or to replicate by other people. For a proxy DNS server you cache what the rest of the world publishes, not the other way around.
  • If no-one has ever asked about names in the domains that you now publish DNS data for, no-one will have cached anything at all.
  • If people have previously obtained answered from somewhere else, then how long they were told those answers were valid — the TTL values on the resource record sets — will determine how long they are cached for.

    user48838 is leading you a bit up the garden path on this one. There is no universal set length for TTL values — 72 hours, 24 hours, or otherwise. They're whatever people choose them to be. In your case, they're currently whatever the people who heretofore were publishing the data chose them to be.

  • If no-one knows that your content DNS server exists, because you haven't asked/told any superdomain owners to delegate domans to you, then what you publish will be simply ignored by the world, because no-one will ever be directed to ask you for it. Arranging delegations involves talking to human beings.

There's a lot of nonsense that people believe when they talk of "DNS propagation", that is based upon a wholly incorrect mental model of how the DNS operates.

  • Your ISP doesn't necessarily have anything to do with things. Your ISP is who shoves IP datagrams between you and the rest of Internet. Your ISP's (resolving proxy) DNS servers have nothing to do with what you, on your machines, choose to publish with DNS content servers.
  • Things are cached for as long as the TTLs say. The resolving proxy DNS servers that the rest of Internet uses (and indeed that you use) will cache data for anywhere up to the entire time-to-live period at the point that they last received those data from a content DNS server.
  • Caching by resolving proxies is quite different to database replication. A set of coöperating content DNS servers replicates a database, with all of the to-be-published data, amongst themselves. This database replication can use one of quite a few mechanisms, from "zone transfer" to simple scp. None of them have anything at all to do with the TTLs on the resource records in the database. Only a few of them even have anything to do with the various replication fields in SOA resource records. And the database replication amongst coöperating content DNS servers has nothing to do with the response caching in proxy DNS servers.
JdeBP
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