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    Posted Jul 27, 2010
    2:13:57 PM
    U-verse ISP DNS cache

    I recently changed hosts for my business website.  This required changing the nameservers for my domain.  It's been about 24 hours, and through my U-verse account here in Atlanta, the domain still brings up my old host.  (Yes I have tried different browsers and cleared the caches on all of them.)  If I connect using another ISP, like my neighbor's or with my Sprint phone, the new website correctly displays.  From what I've read, that means my ISP (U-verse) has not cleared its DNS cache, so it is still mistakenly directing my domain to the old IP address.

     

    So, how long before U-verse clears its DNS cache, and can I do anything to get them to speed up the process?

     

    thanks,

    Mike

    U-verse ISP DNS cache

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    Jul 27, 2010 5:01:28 PM
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    Guru

    DNS updates can take 24-72 hours for any ISP.  Not really anything you can do except wait.

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    Jul 27, 2010 7:05:19 PM
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    Wow, first I hear 24 hours, then 48, now it's up to 72.  Apparently it's not the same for any ISP since other ISP's are resolving correctly.

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    Jul 27, 2010 7:25:43 PM
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    The cache time for a DNS zone is defined in the zone file at the ISP who is hosting DNS for your domain.

     

    You need to ask them what the cache timeout value is set to.

     

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    Jul 27, 2010 7:39:56 PM
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    If that were the case it wouldn't resolve on any ISP.  It works fine on any ISP I've tried except AT&T U-verse.  In fact if I change my DNS servers to bypass AT&T's, it works just fine.  The issue is with AT&T's cache timeout, not that of my host.

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    Jul 27, 2010 8:00:00 PM
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    Scholar

    That will depend on the TTL for your DNS records.  The trick, where possible, is to set a short TTL a few days before you make a change.  Then you can revert to the longer TTL after the change.  (TTL = "time to live").

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    Jul 27, 2010 8:01:28 PM
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    MadDogMike wrote:

    If that were the case it wouldn't resolve on any ISP.  It works fine on any ISP I've tried except AT&T U-verse.  In fact if I change my DNS servers to bypass AT&T's, it works just fine.  The issue is with AT&T's cache timeout, not that of my host.


    No, that's not true.  See the Wikipedia entries for DNS Zone File and for TTL as applied to DNS.

     

     

    If the TTL value is set to a long period (hypothetically, 72 hours), and AT&T's caching DNS server had just refreshed your record before your authoritative ISP changed it, AT&T's caching name server will hold on to the old information for 72 hours.

     

    Whereas other ISPs maybe didn't have the zone cached at all (in which case they pulled the zone and cached it after it was updated), or if their cache had expired or was close to expiration, they got a new copy of the zone from the authoritative nameserver.

     

    Unless you know the exact TTL setting in your DNS zone file, there is no logical implication you can make about whether a fault even exists or not.  Not until you can prove that the TTL value at your authoritative ISP is less than the time that has elapsed since the change in the zone file.

     

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    Jul 27, 2010 8:02:34 PM
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    MadDogMike wrote:

    If that were the case it wouldn't resolve on any ISP.


    Not necessarily.  If the ISP has very few users of your domain, then it might not have the old records in cache.  In that case you see the new data quickly.  With many users of your domain, you will have to wait till the TTL of the cache entries expire.

     

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    Jul 27, 2010 8:07:30 PM
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    Good points, you're all correct.

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